Compostos porfirínicos desempenham uma grande variedade de funções em sistemas biológicos. Em particular, no processo de respiração e na fotossíntese, dois ou mais macrociclos porfirínicos encontram-se próximos na mesma estrutura protéica. A proximidade e a orientação entre os macrociclos são importantes no tipo de função desempenhada; a disposição cofacial entre os macrociclos é um dos fatores responsáveis pelo processo de transferência de elétrons que ocorre nos fotossistemas de organismos fotossintetizantes. Vários estudos têm sido realizados in vitro, com o objetivo de entender o efeito da proximidade e orientação entre os macrociclos nos processos de transferência eletrônica fotoinduzida que ocorrem durante a fotossíntese. Uma das maneiras de construir sistemas miméticos capazes de armazenar luz e transferir elétrons consiste na formação de pares iônicos entre moléculas que apresentam cargas opostas. Apesar da maior versatilidade desses sistemas, não existem estudos sistemáticos que avaliem os efeitos estruturais provenientes da funcionalização dos macrociclos porfirínicos no processo de formação e nas propriedades espectroscópicas de pares iônicos. Esse trabalho apresenta um estudo sobre a formação de pares iônicos entre metaloftalocianinas aniônicas e uma nova classe de porfirinas catiônicas planares e não planares. Através da determinação dos valores das constantes de formação dos heterodímeros, procurou-se avaliar como as características estruturais/eletrônicas dos substituintes β- e meso- do anel se refletem no processo de formação e nas propriedades espectroscópicas dos agregados. Esses estudos foram realizados em diferentes solventes/misturas de solventes e em diferentes forças iônicas, de modo que foi possível avaliar como a mudança do solvente ou da concentração de eletrólito adicionado se reflete no processo de associação entre espécies de carga oposta. As porfirinas não planares utilizadas derivam de uma classe de porfirinas planares que apresentam grupos benzílicos substituídos ligados aos grupos piridínicos presentes nas posições mesa do macrociclo porfirínico; oito átomos de bromo ligados nas posições β-pirrólicas do macrociclo causam a distorção do anel. A introdução de 8 átomos de bromo nas posições β-pirrólicas do macrociclo porfirínico provoca alterações nas propriedades espectroscópicas e fotofísicas das porfirinas, comparando-se as porfirinas β-octabromadas e seus respectivos análogos não bromados. Essa alterações são decorrentes, tanto da distorção do anel, como do efeito de átomo pesado exercido pelos átomos de bromo. Como principais alterações pode-se citar: (i) deslocamento batocrômico dos máximos de absorção e emissão; (ii) redução significativa nos valores de Φfl; (iii) maiores deslocamentos de Stokes; (iv) diminuição nos valores dos tempos de vida do estado excitado triplete; e (v) em função do tipo de solvente empregado, observa-se a coexistência de duas espécies distintas no estado excitado triplete que decaem com tempos de vida distintos. Os valores de KPI obtidos demonstraram que a associação entre as porfirinas catiônicas e as ftalocianinas aniônicas é dependente de uma série de fatores, e pode ser modulada alterando-se o tipo de substituinte ligado ao macrociclo porfirínico e as características do meio, tais como o tipo de sol vente empregado e a força iônica do meio. Os estudos de associação realizados em DMSO demonstraram que (i) a presença do resíduo benzílico traz interações hidrofóbicas adicionais significativas ao processo de associação; (ii) o impedimento estérico decorrente do maior volume do meso-substituinte predomina sobre os efeitos eletrônicos dos grupos ligados na posição para do anel benzílico; e (iii) diferenças na magnitude da distorção da ligação Ni-N e Cu-N para fora do plano, em função da ligação axial a uma molécula de DMSO, se refletem nos valores de KPI. A partir dos estudos realizados em diferentes misturas de solventes, pôde-se constatar que (i) mudanças na esfera de solvatação das porfirinas em meios com maior concentração de H2O alteram os valores de KPI ao longo da série de porfirinas estudadas; e (ii) a formação de dímeros de ftalocianina compete com a formação do heterodímero ftalocianina/porfirina. O controle da força iônica do meio produz alterações significativas nos valores de KPI ao longo da série de porfirinas estudadas. A partir desses experimentos foi possível avaliar o efeito eletrônico dos grupos ligados na posição para do anel benzílico no processo de associação com as ftalocianinas, em relação à ZnTMPyP. A introdução de átomos de bromo no macrociclo porfirínico produz uma série de alterações no processo de associação entre as porfirinas e as ftalocianinas. Durante a associação entre as ftalocianinas e as Zn(II)porfirinas β-octabromadas que apresentaram maiores desvios com relação à planaridade do anel, observou-se a formação de uma espécie trimérica constituída por duas moléculas de porfirina e uma molécula de ftalocianina. Uma vez que ambos os macrociclos encontram-se coordenados axialmente a uma molécula de DMSO, que inviabiliza a formação de um trímero onde os macrociclos se encontram dispostos cofacialmente, este trímero deve ser formado a partir de uma sobreposição parcial entre os macrociclos de carga oposta. Os estudos de fluorescência demonstraram que ocorre uma eficiente supressão da fluorescência da Zn(II)porfirina após a adição de ftalocianina no meio. Demonstraram ainda que esta supressão ocorre através de um processo estático, devido à formação de um complexo de estado fundamental. A avaliação preliminar dos resultados obtidos durante a caracterização do estado excitado triplete dos heterodímeros CuPcTS/ZnP indica que a espécie transiente monitorada na região de 700nm corresponde ao heterodímero presente em solução. Indica ainda que o estado excitado triplete do heterodímero apresenta um caráter de energia predominantemente da ftalocianina. / Macrocyclic tetrapyrroles, like porphyrin derivatives, occur biologically in many enzymes, heme compounds, and photosynthetic protein as chlorophyll. Particularly in the latter, two chlorophylls adopt a face-to-face conformation to form the so-called special pair, the efficient primary electron-donor in the photosynthetic apparatus. It is known that the cofacial arrangement of chlorophylls is a very important feature, because photosynthetic electron transfer process is a function of macrocycle separation and orientation. The complexity of this process has prompted numerous studies of pairing donor-acceptor molecules to mimic the photosynthetic system and understand how the spatial orientation and proximity between the macrocycles affect the fotoinduced electron transfer process. Spontaneous aggregation between porphyrins and phthalocyanines bearing charged peripheral substituents occurs in solution, and thus, these molecules have been employed to study face-to-face heterodimer bound electrostatically. Despite the fact that these systems share many of the characteristics of naturally occurring special pair, there is no systematic study assessing the structural effects of functionalized porphyrin rings on the association process for anionic macrocycles. This work reports a heterodimer formation between anionic phthalocyanines and a new class of cationic planar and non planar porphyrins. Heterodimers have been characterized by determining the formation equilibrium constants (KPI) in different media and ionic strength. The new class of non planar cationic Zn (II) porphyrins synthesized presents eight bromine atoms attached to the β-pyrrole position of the porphyrin ring, leading to a high degree of distortion. The planar cationic precursor presents substituted benzylic groups attached to the nitrogen atoms of the pyridyl residues located at the meso-porphyrin positions. Both ring distortion and heavy atom effect caused by the introduction of bromine atoms at the macrocycle periphery cause many changes in the spectroscopic and photophysical properties, comparing to the planar precursor. The main differences observed are: (i) batochromic shifts of absorption and emission maxima; (ii) lower fluorescence quantum yields; (iii) larger Stokes shifts; (iv) reduced triplet lifetimes and; (v) depending on the solvent employed, it was observed the coexistence of two distinct species in the excited triplet state that posses different lifetimes. According to the KPI values obtained, it was inferred that the association process can be modulated by changing the meso- and β-substituent attached to the porphyrin ring, and altering medium characteristics. The KPI values obtained in DMSO solution suggest that steric hindrance from benzylic groups overwhelms the additional hydrophobic/eletronic effects from these meso-substituents. When the ionic strength was kept constant, a decrease in the KPI values was observed, as expected to the association between ionic species. It could be noted, therefore, that the additional hydrophobic contribution from benzylic substituent, and also the electronic characteristics of the small groups attached to the benzylic ring affect the association process. From experiments carried out in solvent mixtures, it could be observed that, if the solvent dielectric constant increases, the KPI values decrease. Likewise, changes in the porphyrin macrocycle solvation alter the KPI value through the porphyrin serie studied. Additionally, as the water concentration increases, the phthalocyanine self-association process competes with heterodimer formation. The introduction of bromine at ring periphery changes the association process. The KPI values obtained to the heterodimer formed between the anionic phthalocyanines and the β-octabrominated porphyrins, are about 10 times smaller compare d to the KPI obtained using the planar precursor. It is a consequence of nonplanar distortion, that diminishes the cofacial approximation between the macrocycles. Addi tionally, heterotrimers can be formed by altering the porphyrin concentration - this behavior was not found to the aggregates formed between the phthalocyanines and the planar precursor derivatives at the same condition. Emission studies evidence a ground state complex formation, since the phthalocyanine quenches the Zn (II) porphyrin fluorescence through a static process. The preliminary results obtained to the heterodimer triplet characterization showed that the heterodimer excited triplet state is more delocalized on the phthalocyanine moiety.

This thesis is concerned with the photophysical and nonlinear optical responses, and applications of a set of conjugated polymers and small molecules in the visible and near-IR spectral regions. Poly(phenylene ethynylene) PPE polymers were substituted with conjugated side-arms in a cruciform fashion to determine the impacts of electronic coupling on the one-photon (1PA), two-photon (2PA), and excited state absorption (ESA) properties of the co-polymer system. The cruciform-like PPEs showed significant changes in their nonlinear and phophysical behavior relative to their linear models, including shifts and splittings of the 1PA bands due to moderate mixing of the lowest singlet excited states, an increase in the 2PA cross section (δ) values, and an increase in the yield of triplet excited-state species. The cruciform-like PPE polymers exhibited effective optical pulse suppression of femtosecond and nanosecond laser pulses over a broad spectral range of ~200 nm in the visible and near-IR. The suppression capability of the cruciform-like PPEs exceeded the best reported value for alkyl-substituted PPE polymers. The spectroscopic effects due to conjugation length, structural configuration, and intramolecular charge transfer (ICT) are discussed for a family of bent donor-acceptor-donor (D-A-D) -type conjugated oligomers, which incorporate electron-rich triarylamine donors and electron-deficient triarylborane acceptor units into its conjugated structure. These organoborane oligomers are highly fluorescent and exhibit strong 2PA in the visible region with δ values as large as 1410 GM, as well as overlapping ESA bands attributed to singlet-singlet and triplet-triplet absorption. Saturation of the molar absorptivity, ε, and δ was observed at less than two repeat monomer units due to conformational disorder in the oligomer with increasing length. Positive solvatochromism of fluorescence with solvent shifts as large as ~70 nm was observed as a result of ICT from the arylamine donors to boryl-centered acceptor sites. The excited-state dynamics also show sensitivity to the solvent environment. Experimental findings suggest that these organoborane oligomers may have potential use as nonlinear material for optical power limiting (OPL) and two-photon sensing applications. The spectral properties of two bis-donor chromophores, (bis(diarylamino)biphenyl (TPD) and distyrylthiophene (DST), were investigated with and without the presence of AgNPs in order to better understand the local-field enhancement and subsequent effects on the photophysics and nonlinear behavior of 2PA dyes. While little changes were observed in the excited-state dynamics, measurements of nanoparticle aggregate-dye composite solutions with TPD revealed a 1.6-enhancement in the two-photon excited fluorescence signal. OPL measurements of nanosecond laser pulses at 532 nm revealed a reduction in threshold energy by a factor of 2 in solutions containing TPD and AgNP aggregates, relative to solutions of TPD alone. DST shows exceptional solubility (>1 M) in several organic solvents and exhibits a 2PA spectrum that overlaps well with its singlet-singlet and triplet-triplet ESA bands. Consequently, DST exhibits effective optical limiting of nanosecond laser pulses through two-photon induced excited-state absorption over a broad spectral range of approximately 200 nm in the red and near-IR.

No description available.

Magister Scientiae - MSc (Chemistry) / This work involves the synthesis of copper telluride-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuTe@PPI) and copper antimonide-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuSb@PPI) core-shell nanoparticles (NPs), using two-pots and one-pot synthesis methods, respectively. Their morphology was studied by X-ray diffraction spectroscopy (XRD), high resolution transmission electron microscopy (HRTEM) and high resolution scanning electron microscopy (HRSEM); while their structures were characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. Photophysical properties of the core-shell NPs were determined from ultraviolet-visible absorption spectroscopy (UV-Vis) and photoluminescence spectroscopy (PL). For core-shell NPs produced via two-pots method only CuTe@PPI exhibited ? ? ?* and n ? ?* which indicate that CuSb@PPI produced via two-pots method was unsuccessfully synthesized. The ? ? ?* and n ? ?* transitions indicate the presence of polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (PPI) on the surface of CuTe NPs and CuSb NPs. FTIR confirmed coordination of PPI on the surface of CuTe NPs and CuSb NPs by showing a shift in wavenumber of C=N group bands from PPI. HR-TEM showed that the CuTe@PPI synthesized via one-pot method have a wide particles sizes distribution with an average particles size of 13.60 nm while for CuTe@PPI synthesized via two-pots it was impossible to determine the particles size due to aggregation. CuSb@PPI synthesized via twopots method and one-pot method has a wide particles sizes distribution with an average size of 7.98 nm and 11.61 nm respectively. The average particles sizes determined by HR-SEM were found to be 35.24 nm (CuTe@PPI two-pots method), 33.90 nm (CuTe@PPI one-pot method), 18.30 nm (CuSb@PPI two-pots method), and 16.18 nm (CuSb@PPI one pot method). / 2021-08-31

This Ph.D. thesis is an exploration of carotenoids by ultrafast, time-resolved absorption spectroscopy to investigate their complicated relaxation processes, means of energy transfer, and dependence on structure. The introduction begins with an overview of carotenoids, intended for the reader to appreciate their importance and their complexity as revealed by decades of research in carotenoid photophysics. To understand the primary concerns of this research field, the reader is guided through basic theory of energetic processes, the experimental method, and methods of analysis. The main body of the text is the Research Chapter, containing four sections, each describing research using varied ultrafast transient absorption spectroscopies on carotenoids in solution and when bound to a host protein. Section 2.1 concerns an equilibration phenomenon in the lowest excited state of the carotenoid fucoxanthin in various solutions and temperatures by a multi-pulse transient absorption method. The same method is applied to fucoxanthin in a host antennae protein of the pennate diatom Phaeodactylum tricornutum to investigate the function of the equilibration in energy transfer to Chlorophyll a in Section 2.2. The next two sections regard the effect of carotenoid structure on its relaxation dynamics. Section 2.3 investigates the effect of the non-conjugated acyloxy group of two fucoxanthin derivatives in various solvents. Here, one of the energetic states involved in the equilibrium mentioned above is seen drastically affected. Lastly, Section 2.4 investigates alloxanthin, a carotenoid with an unusual pair of carbon-carbon triple bonds. Their effect on the conjugation is evaluated based upon the molecules' decay dynamics. A general summary and conclusion is provided at the end.

Au cours du 21ème siècle, les techniques de fluorescence ont montré une expansion considérable dans l’étude du mécanisme du vivant. Un progrès majeur dans le développement, la conception et les applications de divers types de chromophores organiques ont été achevés. Bien que largement utilisés, les sondes fluorescentes les plus utilisées souffrent encore de quelques limitations qui diminuent leur étendue d'action. Les plus problématiques sont : un nombre restreint de familles de chromophores, une faible résistance au photoblanchiment, une faible solubilité aqueuse, une durée de vie de fluorescence relativement courte, etc…. A ce titre, le développement de nouveaux motifs organiques inédits, compacts et possédants des propriétés de fluorescence alternatives et/ou complémentaires aux fluorophores usuels organiques reste plus que jamais d’actualité. Dans ce contexte, les noyaux 1,3a, 6a-triazapentalènes nous sont apparus particulièrement prometteuses et encore très peu exploitées. Dans ce manuscrit, il est décrit la synthèse de noyaux tricycliques et tétracycliques comportant ce motif, obtenus par substitution nucléophiles aromatiques, suivi d’une thermolyse. La modulation de ces noyaux a ensuite été effectuée par couplage métallo-catalysé. L’évaluation photophysique de ces composés révèle des propriétés spectroscopiques remarquables comme des rendements quantiques supérieurs à 50%, des déplacements de Stokes d’environ 100 nm et des longueurs d’ondes d’émission allant de 450 à 650 nm. Le dernier volet de cette thèse a porté sur l’imagerie cellulaire, qui nous a permis d’évaluer les meilleurs fluorophores sur cellules vivantes. / Over the last two decades, fluorescence technologies have shown a spectacular spreading in biological research. Major progress in the development, design, and purposeful application of various types of organic chromophores was achieved. Although widely used, the most commonly fluorescent probes still suffer from some limitations which decrease their use in the field of life sciences. The most problematic ones are: low scaffold diversity, high sensitivity to photobleaching, low water solubility and modest Stokes Shift… In this context, the main idea of our work focuses on the development of novel organic motifs responding to the conventional fluorophores issues. The 1,3a, 6a-triazapentalene moiety represents a real interest in this field with its promising optical properties. In this manuscript, the syntheses of tricyclic and tetracyclic derivatives containing this scaffold were obtained by aromatic nucleophilic substitution followed by the thermolysis cyclization. The modulation of these cores was then allowed by various organometallic cross of these compounds provides remarkable spectroscopic properties, as quantum yields above 50%, Stokes shift around 100 nm, and emission wavelengths between 450 and 650 nm. The last part of this thesis was focused on cellular imaging, that allowed us to evaluate the best fluorophores in living cells.

Orientadora: Prof.ª Dr.ª Karina Passalacqua Morelli Frin / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2016. / Quatro compostos polipiridinicos de Re(I), fac-[Re(CO)3(ph2phen)(L)]+ (L = bpa, 4,4¡¦-bpy e, apy) e fac-[{(Ph2phen)(CO)3Re}2(bpa)]+2, foram sintetizados e purificados. Os complexos foram caracterizados por espectroscopia de 1H RMN, IR/ATR e UV-vis em MeCN a 298 K. Foi verificado intensa absortividade (4.104 Lmol-1cm-1) na regiao UVB (£fmax =292 nm) do espectro atribuida a transicao intraligante 1ILPh2phen, e a transicao de transferencia de carga do metal para o ligante 1MLCTRe ¿_ Ph2phen (1.104 Lmol-1cm-1) em aproximadamente £f ~350 nm. As propriedades fotofisicas produzem 3MLCT Re ¿_ Ph2phen que apresentam intensa luminescencia em £fem = 562 nm usando-se excitacao em comprimento de onda monocromatico de 375 nm possuindo rendimento quantico de emissao (¿Öem) da ordem de 0,036-0,360 e tempo de vida de emissao (£n) de £gs, sendo que a luminescencia observada varia em funcao do carater doador e aceptor de densidade eletronica do ligante (L) definindo a basicidade e acidez dos complexos em solucao. As propriedades fotofisicas em pol (metacrilato de metila) PMMA exibiram o efeito rigidocromico observado por meio do deslocamento hipsocromico da emissao sem alteracao na estrutura da banda 3MLCT Re Ph2phen. O estudo de supressao com hidroquinona (H2Q) em solucao desaerada de MeCN a 298 K demonstrou excelente correlacao entre intensidade de emissao (I) e tempo de vida de emissao (£n) dos complexos na metodologia de Stern-Volmer. Para os complexos fac-[R (CO)3(Ph2phen)(bpa)]+, fac-[Re(CO)3(Ph2phen)(4,4¡¦-bpy)]+ e fac-[{(Ph2phen)(CO)3Re}2(bpa)]2+ foram determinadas as constantes Ksv da ordem de 104 Lmol-1 com correspondentes constantes cineticas de supressao bimolecular kq 109 Lmol-1s-1 revelando forte supressao do estado excitado associado ao mecanismo dinamico de transferencia de eletron (ET) por meio de interacoes/empilhamento £k-£k* como sugestao de rota mais eficiente. Enquanto, para o complexo fac-[Re(CO)3(Ph2phen)(apy)]+ a constante Ksv obtida foi de 102 Lmol-1 e, kq 109 Lmol-1s-1, demostrando evidencias de um caminho alternativo para supressao desse composto com H2Q envolvendo um possivel mecanismo dinamico de supressao via transferencia protonica acoplada a transferencia de eletron (EPT) que e menos eficiente, assumindo-se a existencia de intrinseco pre-equilibrio acido-base desse complexo em solucao. / Four polypyridyl Re(I) compounds, fac-[Re(CO)3(ph2phen)(L)]+ (L = bpa, 4,4¡¦-bpy e, apy) and fac-[{(Ph2phen)(CO)3Re}2(bpa)]+2, were synthesized and purified. The complexes have been characterized by 1H NMR, IR/ATR and UV-vis spectroscopies in MeCN at 298 K. Verified intensity absorption (4.104 Lmol-1cm-1) in UVB spectral region (£fmax = 292 nm) assigned to the intraligand 1ILPh2phen transition, and the metal-to-ligand charge transfer 1MLCTRe ¿_ Ph2phen transitions (1.104 Lmol-1cm-1) in about £f ~350 nm. The photophysical properties produces 3MLCT Re ¿_ Ph2phen which account for stronger luminescence in £fem = 562 nm using monochromatic excitation 375 nm resulting in emission quantum yields (¿Öem) in the range of 0,036-0,360 and lifetimes (£n) of the order of £gs, wherein the luminescence observed as a function of the donor or acceptor of electron density of the ligand (L) defining the basicity and acidity of the complexes in solution. The photophysical properties in poly(methyl methacrylate) PMMA exhibited the rigidochromic effect observed by hypsochomic shifts in spectra with no change in the emission band structure 3MLCT Re ¿_ Ph2phen. The quencher studies by hydroquinone (H2Q) in degassed MeCN solution at 298 K demonstrated excellent correlation between emission intensity (I) and lifetime (£n) for the complexes using Stern-Volmer methodology. For fac-[Re(CO)3(Ph2phen)(bpa)]+, fac-[Re(CO)3(Ph2phen)(4,4¡¦-bpy)]+ and fac-[{(Ph2phen)(CO)3Re}2(bpa)]2+ complexes were determined Ksv constant in 104 Lmol-1 order, and the corresponding rate constant for the bimolecular excited state quenching kq 109 Lmol-1s-1 revealed stronger excited-state quenching associated with the dynamic mechanism of the electron transfer (ET) by £k-£k* stacked suggesting a more efficient pathway. While for the fac-[Re(CO)3(Ph2phen)(apy)]+ complex the Ksv obtained constant was 102 Lmol-1 and respective kq = 109 Lmol-1s-1 demonstrated the evidence of an alternate path for quenching that compound by H2Q involving a possible less efficient dynamic mechanism the electron-proton-transfer (EPT) assumed the intrinsic preequilibria acid-base that complexes in solution.

Neste trabalho foram estudadas as propriedades fotoquímicas e fotofisicas do composto bi-cromofórico 1-(2-quinolil)-2-naftol (2QN). Este composto reúne dois sistemas prototrópicos de estado excitado intermoleculares bem conhecidos (2-naftol, fotoácido e quinolina, fotobase) para um sistema intramolecular. Esta escolha deveu-se à conveniência dos pKa\'s e pKa*\'s e tempos de vida de estado excitado do 2-naftol (2N) da quinolina (Q), os quais, em princípio, permitem reações prototrópicas de estado excitado em solução neutra. Desta transformação de sistema inter para intramolecular especula-se obter um \"precursor\" para obtenção de polímeros condutores de prótons. Através dos espectros de absorção e fluorescência, verificou-se que os dois cromóforos do 2QN se comportam independentemente, porém os rendimentos quânticos de fluorescência ( &#934;f) em toda faixa de pH e em vários solventes orgânicos são muito menores que aqueles dos compostos isolados. Esta diminuição de &#934;f é atribuida ao efeito supressivo do cromóforo vicinal. Através dos espectros de fluorescência em solventes orgânicos (Acetonitrila, Hexano e EtOH) sugere-se a ocorrência de transferência de próton intramolecular. Calculou-se via ab initio pelo método restrito Hartree-Fock (RHF) utilizando-se o programa Gaussian a estrutura do 2QN e obteve-se um ângulo diedro de ~42º entre dois cromóforos que impede a rotação livre dos mesmos. Resultado este em boa concordância aos de difração de R-X (~39º). Observou-se a reação fotoquímica induzida por UV do 2QN em solventes alcoólicos (EtOH, MeOH). O fotoproduto foi caracterizado por espectroscopia de RMN (1H, 13C, Dept, COSY e Hetcor), CG-Massa e Infra-vermelho. O fotoproduto principal obtido sugere um mecanismo de reação via SN1Ar intramolecular pelo ataque do átomo de oxigênio do naftolato ao grupo quinolínico. Além do 2QN preparou-se os derivados 2QNCH2+I- e 2QNCH3+I- (compostos inéditos) para auxiliar as atribuições acima. Em matrizes vítreas orgânicas observa-se um drástico aumento em &#934;f e de fosforescência atribuídos ao decréscimo do grau de liberdade rotacional dos rotâmeros do 2QN. Finalmente pelo espectro de luminescência em fase sólida sugere-se a transferência de próton intra- e intermolecular o que ressalta a interesse do 2QN tanto de suas propriedades intrínsecas prototrópicas, quanto como precursor para um sistema supramolecular fotoativado de transferência de prótons. / In this work the photochemical and photophysical properties of the bichromophore 1-(2-Quinolyl)-2-Naphthol (2QN) were studied. This compound associates two well known excited stated intermolecular prototropic systems (2-Naphthol, photoacid and Quinoline, photobase) into an intramolecular system. The convenience of the pKa\' s, pKa*\' s and excited state lifetimes of 2-Naphthol and of Quinoline allows in principle excited state prototropic reactions in neutral solutions. From this transformation of an intermolecular to an intramolecular system it is speculated to obtain a precursor for a proton conductor polymer. The two chromophores of 2QN were found to behave independently by absorption and fluorescence analysis, however, the fluorescence quantum efficiency (&#934;F) at all pH\' s as well in various organic solvents is much smaller than that of isolated compounds. The decrease in <!>F is attributed to the quencher effect of the vicinal chromophore. From the fluorescence spectra in organic solvents (Acetonitrile, Hexane and EtOH), the occurrence of intramolecular proton transfer is suggested. Ab initio calculations by the restricted Hartree-Fock (RHF) using Gaussian program modeled the structure of 2QN with a dihedral angle ~42º between two chromophore planes that hinders the :free rotation. A result in good agreement with that found by X-ray diffraction (~39º). A UV induced photochemical reaction at 2QN in alcoholic solvents (EtOH, MeOH) is observed. The photoproduct was characterized by NMR (1H, 13C, Dept, COSY and Hetcor), GC-mass and IR spectroscopy. The main photoproduct suggests a SN1Ar reaction mechanism by the attack of the naphtholate oxygen on quinolinium. Besides 2QN, two new derivatives 2QNCH2+I-and 2QNCH3+I- (new compounds) were prepared in order to better establish the attributions above. In organic glassy matrixes a drastic increase of &#934;F and of phosphorescence attributed to the decrease in rotational (librational) mobility of 2QN\' s is observed. Finally, from the luminescence spectra in solid phase both intra- and intermolecular proton transfer is suggested, pointing out the interest in the study of 2QN to generate a proton transfer supramolecular photoinduced system.

Esta tese focou em três tópicos principais: caracterização de filmes compactos de TiO2 e seu comportamento em células solares sensibilizadas por corante; estudo das propriedades fotoquímicas e fotofísicas de um complexo fotoisomerizável de rênio(I); elucidação das propriedades fotofísicas e eletrônicas de complexos de irídio(III) e suas aplicações em dispositivos emissores de luz. Filmes compactos foram automontados nos fotoanodos de células solares sensibilizadas por corante (DSCs), sob o filme mesoporoso de TiO2/corante, utilizando sols de TiO2 ácidos e básicos como cátions e ânions, respectivamente. A obtenção dos sols foi realizada sob controle absoluto para resultar em propriedades morfológicas e ópticas apropriadas para filmes compactos de alta qualidade, como indicado por perfilometria e microscopia eletrônica de transmissão e varredura. As DSCs com bicamadas de TiO2 melhoraram as eficiências de conversão em até 62%. Uma investigação detalhada por parâmetros fotoeletroquímicos, IPCE, tempo de vida do elétron e espectroscopia de impedância eletroquímica demonstrou que o contato entre o vidro condutor (FTO) e o TiO2 é melhorado e que a recombinação de carga no FTO/I3- é diminuída. O novo complexo fac-[Re(CO)3(Ph2phen)(trans-stpyCN)]+ foi sintetizado para apresentar o intercâmbio entre as configurações trans e cis do ligante coordenado por meio de fotoisomerizações eficientes e reversíveis. As fotólises em 313, 334, 365 e404 nm resultam em mudanças espectrais no UV-Vis e RMN atribuídas à fotoisomerização trans-cis do ligante stpyCN coordenado. O processo reverso cis-trans também foi observado com irradiação em 255 nm, com um notável rendimento quântico (&#934 = 0,16), de mesma magnitude que para o processo trans-cis (&#934; = 0,38). A caracterização fotofísica e os espectros de absorção do transiente corroboraram na atribuição de um comportamento incomum para os estados excitados quasedegenerados 3ILstpyCN e 3MLCTRe&#8594;Ph2phen. Complexos heterolépticos de Ir(III) foram sintetizados e suas propriedades fotofísicas avaliadas, como rendimentos quânticos e tempos de vida de emissão, constantes radiativas e não-radiativas e coordenadas CIE. Os parâmetros fotofísicos variaram sistematicamente com variações nos substituintes retiradores ou doares de elétrons, como corroborado por cálculos TD-DFT, que mostraram uma mistura de estados excitados IL-MLCT. Três desses complexos foram utilizados na camada ativa de dispositivos emissores de luz e caracterizados optoeletronicamente por curvas de corrente-brilho-potencial e espectros eletroluminescentes. / Three main topics are discussed in this thesis: characterization of TiO2 compact films towards high-performance dye-sensitized solar cells; investigations of photophysical and photochemical processes of a Re(I) complex; photophysical elucidation of Ir(III) complexes and their application in light emitting devices. All-nano-TiO2 compact films were auto-assembled in the photoanodes of dyesensitized solar cells (DSCs), beneath the TiO2 mesoporous film, employing acid and basic nano-TiO2 sols as cations and anions, respectively. TiO2 syntheses were performed under absolute control to lead to appropriate morphological and optical properties to yield high quality compact films, as indicated by profilometry, tunning and scanning electron microscopy. DSCs with TiO2 bilayers on top of the conducting glass (FTO) improved the conversion efficiency up to 62%. A detailed study by photoelectrochemical parameters, IPCE, electron lifetime and electrochemical impedance spectroscopy demonstrates that the contact between FTO and TiO2 was improved and that the FTO/I3- charge recombination was prevented. The novel fac-[Re(CO)3(Ph2phen)(trans-stpyCN)]+ complex was synthesized to show switchable trans-cis configurations of the coordinated stpyCN ligand through efficient and reversible photoassisted isomerizations. Photolyses at 313, 334, 365 and 404 nm led to UV-Vis and NMR spectral changes ascribed to the trans-to-cis photoisomerization of the coordinated ligand. The reverse cis-to-trans process was alsoobserved at 255 nm irradiation, with a remarkable quantum yield (&#934; = 0.16), in the same magnitude to the one for trans-to-cis photoprocess (&#934; = 0.38). Photophysical characterization and transient absorption spectra provided insights on the light-driven trans ? cis pathways and indicated an unusual behavior for the 3ILstpyCN excited state, induced by an interplay with the quasi-degenerated 3MLCTRePh2phen state. Heteroleptic Ir(III) complexes were synthesized and phophysical properties evaluated, such as emission quantum yields and lifetimes, radiative and non-radiative constants and CIE coordinates. The photophysical parameters varied systematically with variations in electron-donating or -withdrawing substituents on the ligands, as corroborated by TD-DFT calculations that showed an IL-MLCT mixing in their emissive excited state. Three complexes were employed in the active layer of light emitting devices and had their optoeletronic properties characterized by current-brightness-voltage curves and electroluminescent spectra.

Solvent effects play diverse roles in myriads of chemical, physical and biological processes. The solvent interacts with the solute by: i) non-specific (Coulombic, van der Waals interactions) and ii) specific interactions (hydrogen bonding, etc.). These interactions are responsible for solvation of the solute and are collectively termed as “solvent polarity”. Differential solvation of ground and excited electronic states is manifested in the absorption spectrum as a change in the band position, intensity or shape, which is termed as “solvatochromism”. Intermolecular hydrogen bonding (IHB) is a kind of specific solute-solvent interaction, which plays a key role in molecular or supramolecular photochemistry, as well as in photobiology. Solvation and its influence on various physico-chemical and biological processes can be understood by i) top-down; and ii) bottom-up approaches. In the top-down approach, the macroscopic properties like dielectric constant, refractive index are used to understand the microscopic solvation. This approach fails when specific interactions like hydrogen bonding interactions come into play, and furthermore it can reproduce only the macroscopic polarization of the solvent but fails miserably at the cybotactic region of solvation. With the recent advancements in the computational field, the molecular level description of solvation has been within reach for chemical physicists and experimentalists to corroborate their experimental results and in turn to visualize processes of fundamental or technologically relevant problems. The energy levels of the nπ* and ππ* singlet and triplet excited states of aromatic ketones are close-lying and therefore their energy levels can be altered by the substituents. The solvent polarity can be used as a surrogate to tune their energy levels. In certain cases, the lowest triplet or singlet excited states can switch their electronic character with increasing solvent polarity known as “electronic state switching” and thus modulate their photochemical or photophysical properties. Therefore, aromatic ketones were used as solvatochromic probes in this work. Comprehensive analyses of the solvent effects on xanthone (XT), 9,10-phenanthrenequinone (PQ) and benzophenone (Bzp) were carried out using steady-state and nanosecond time-resolved absorption, and resonance Raman spectroscopy in conjunction with ad hoc and classical-molecular dynamics and simulations generated supermolecule-continuum solvent model quantum mechanical calculations to corroborate the experimental outcomes and in turn to visualize the solvation process at the molecular level. The present thesis is divided into eight chapters and the summary of each chapter is described below: Chapter 1 provides a brief literature review of solvation effects and their influence on various physico-chemical and biological processes. Furthermore, the importance of understanding solvation at the molecular level and key concepts are discussed, which forms the heart of this thesis. Chapter 2 discusses the experimental and computational approaches used to study the solvation processes at the molecular level. A detailed explanation of spectroscopic techniques like resonance Raman (RR) and nanosecond-time resolved resonance Raman (ns-TR3) spectroscopy and their experimental and theoretical aspects are discussed, followed by a discussion on the fundamental concepts of computational methods like ab initio calculations density functional theory (DFT), and classical molecular dynamics and simulations (c-MDS) utilized in this study. Chapter 3 focuses on microscopic understanding of solvatochromic shifts observed for 9,10-phenanthrenequinone in protic solvents using UV-Vis and RR spectroscopy in conjunction with an ad hoc explicit solvation model and time-dependent density functional theory (TDDFT) calculations. The hypsochromic shift and bathochromic shift of the singlet nπ* and ππ* electronic transitions in protic solvents are due to hydrogen bond weakening and strengthening in the excited state for the corresponding electronic transitions, respectively as indicated by TD-DFT calculations and Kamlet-Taft linear solvation energy relationships. The hydrogen bond strengthening in the singlet ππ* excited state is further confirmed by Raman excitation profile (REP) analysis of PQ in different solvents. Furthermore, with increasing solvent polarity the two lowest singlet excited states undergo different hydrogen bonding mechanisms, leading to a decreasing energy gap between them. Therefore, hyperchromism of the nπ* transition has been hypothesized to be due to an increasing vibronic coupling between the lowest singlet nπ* and ππ* excited states. In Chapter 4, a real time observation of the thermal equilibrium between the lowest triplet excited states of PQ in acetonitrile solvent was carried out using ns-TR3 spectroscopy and this can explain its high reactivity towards H-atom abstraction, despite the fact that the lowest triplet excited state has ππ* character. Furthermore, extending the concept of hydrogen bonding mechanisms of the lowest singlet to the triplet excited states, the different hydrogen bonding mechanisms exhibited by them can lead to alteration of the intersystem crossing mechanisms in PQ. Chapter 5 highlights the very different role of intermolecular hydrogen bonding in the reduced reactivity of the xanthone (XT) triplet towards H-atom abstraction in protic solvents. The different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states in protic solvents are derived from an ad hoc explicit solvation model, TD-DFT calculations and ns-time resolved absorption (ns-TRA): they separate them further in energy and thereby the nearest T2(nπ*) triplet state to the T1(ππ*) excited state plays an insignificant role in the reactivity towards H-atom abstraction, in contrast to the PQ triplet discussed in Chapter 4. Chapter 6 discusses the structure of XT triplet states using TR3 spectroscopy in combination with TD-DFT studies. The TR3 spectrum of the XT in acetonitrile identified a vibronic coupling mode responsible for the reactivity of XT towards H-atom abstraction, despite the fact that the lowest triplet excited state (T1) has ππ* character. This vibronic active mode is absent in the TR3 spectra of XT in protic solvents (methanol and ethanol). Furthermore, the REP analysis suggests that the nanosecond triplet-triplet absorption spectrum of XT in acetonitrile involves two different species, while in methanol it involves only one species. This observation is in agreement with the previous chapter (Chapter 5) which proposes a different hydrogen bonding mechanisms for the two lowest triplet excited states and their influence on the reduced reactivity towards H-atom abstraction. Chapters 3-6 emphasize the need for a proper solvation model at the molecular level to describe the various photophysical and photochemical processes of aromatic ketones. Therefore, Chapter 7 includes discussions on the bottom-up solvation methodology applied to benzophenone (Bzp) to understand its vibrational and electronic solvatochromic behaviour at the molecular level. Raman and UV-Vis spectroscopic techniques were used in conjunction with a c-MDS-generated supermolecule continuum solvation model DFT calculation to corroborate and to visualize the experimental outcome. The carbonyl stretching frequency of Bzp in protic solvents has two bands, corresponding to free carbonyl and hydrogen bonded carbonyl. Despite the fact that the macroscopic polarity of acetonitrile and methanol solvents are similar, the free carbonyl stretching of Bzp in methanol solvent was blue-shifted by 4 cm-1 with respect to the carbonyl stretching in acetonitrile solvent. The Gutmann’s acceptor number plot for carbonyl stretching frequencies indicates that the free carbonyl group is neighboured by a hydrophobic environment. The c-MDS-generated supermolecule-continuum solvation model DFT calculations suggest that the extended hydrogen bonding network of methanol solvent is responsible for the hydrophobic solvation around the free carbonyl. Furthermore, a linear correlation was obtained for the vibrational and electronic solvatochromism of the carbonyl frequency and energy of the singlet nπ* transition, respectively, which indicates that a variation in excitation wavelength for the singlet nπ* transition can arise from different solvation states. This can have implications for ultrafast processes associated with electron transfer, charge-transfer and also the photophysical aspects of excited states.Finally, Chapter 8 contains overall conclusions of the thesis and future directions for the present research area.