Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work reports on the optical properties of chalcones molecules in solution, using methanol as solvent. For the characterization of the linear optical properties, were obtained absorbance spectra. While for the characterization of the nonlinear optical properties, it has been used techniques hyper-Rayleigh scattering and Z-scan. Using hyper-Rayleigh scattering technique, were determined the first hyperpolarizabilities of the molecules studied. With the Z-scan technique, we could obtain the two-photon absorption spectra at several wavelengths in the range of 480 to 790 nm. From the two-photon absorption spectra were possible to determine the coefficients of two-photon absorption and their respective cross section. The results help to understand the effects of substituents added to the basic structure of chalcones in both linear optical properties as nonlinear. / Neste trabalho, estudamos as propriedades ópticas de moléculas de chalconas em solução, usando o metanol como solvente. Para a caracterização das propriedades ópticas lineares foram determinados os espectros de absorção. Na caracterização das propriedades ópticas não lineares foram utilizadas as técnicas de espalhamento hiper-Rayleigh e de varredura-Z. Utilizando a técnica de espalhamento hiper-Rayleigh foram determinadas as primeiras hiperpolarizabilidades das moléculas estudadas. Com a técnica de varredura-Z conseguimos obter os espectros de absorção de dois fótons em vários comprimentos de onda no intervalo dos 480 aos 790 nm. A partir dos espectros de absorção de dois fótons foi possível determinar o coeficiente da absorção de dois fótons e sua respectiva seção de choque. Os resultados ajudam a compreender os efeitos de substituintes, adicionados à estrutura básica das chalconas, tanto nas propriedades ópticas lineares quanto não lineares.

Compostos orgânicos constituem uma classe interessante de materiais para aplicações em óptica por apresentarem boa processabilidade, relativa facilidade para integração em dispositivos e, principalmente, pela possibilidade de otimização de suas propriedades ópticas através da engenharia molecular. Várias estratégias têm sido empregadas para sintetizar moléculas orgânicas, que exibam singificativos efeitos ópticos não lineares. Nesta direção, nos últimos anos moléculas multi-ramificadas vêm sendo produzidas com o objetivo de intensificar efeitos não lineares, já que estas podem exibir um forte efeito cooperativo entre seus ramos. Nesta tese estudamos a relação da absorção de dois fótons (A2F) e da primeira hiperpolarizabilidade com a estrutura molecular, para um conjunto de nove derivados de trifenilamina com diferentes grupos aceitadores de elétrons arranjadas em geometrias dipolar, quadrupolar e octopolar. O processo A2F foi estudados através da técnica de Varredura-Z, enquanto que a primeira hiperpolarizabilidade foi caracterizada pela técnica de espelhamento hiper Rayleigh. Os dados experimentais para a absorção de dois fótons revelaram espectros bem definidos, com valores razoáveis de seção de choque na região do visível e infravermelho próximo. Observamos ainda um engrandecimento para a seção de choque de A2F para as moléculas quadrupolares. Os resultados obtidos para a primeira hiperpolarizabilidade (β) mostraram que moléculas quadrupolares apresentam maior β do que as dipolares e octopolares, portanto, nossos resultados permitem concluir que o acoplamento eletrônico entre os ramos contribuem fortemente para a seção de choque por A2F e β nas moléculas quadrupolares, não sendo este processo relevante nas moléculas octopolares. Todos os resultados foram interpretados por meio de estudos teóricos empregando a teoria do funcional da densidade (DFT). / Organic compounds constitute an interesting class of materials for optical applications due to their excellent processability, easy integration into devices and, mainly, the possibility of optimizing its optical properties through molecular engineering. Several strategies have been employed to synthesize organic molecules, which exhibit significant nonlinear optical effects. In this direction, in the last few years multi-branched molecules have been obtained aiming at intensifying nonlinear optical effects, since they may exhibit a strong cooperative effect among their branches. On this thesis we have studied the relationship of two-photon absorption (2PA) and first hyperpolarizability with the molecular structure of a group of nine triphenylamine derivatives attached to distinct electron acceptor groups arranged in dipole, quadrupole and octopolar geometries. The 2PA process was studied by Z-scan technique, while the first hyperpolarizability was characterized by the hyper-Rayleigh scattering technique. The experimental data for two-photon absorption revealed well-defined spectra with reasonable cross section magnitude in the visible and near infrared range. We also observed an enhancement of the 2PA cross-section for the quadrupolar molecules in comparison to the dipolar and octopolar ones. The results obtained for the first hyperpolarizability (β) shown that the quadrupolar molecules present higher β than the dipolar and octopolar, suggesting that the electronic coupling between the branches strongly contribute to the 2PA cross-section and β in quadrupolar molecules, being not relevant in the octopolar molecules. All results were interpreted through theoretical studies based on the density functional theory (DFT).

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-05-08T11:42:32Z No. of bitstreams: 1 diegofernandodasilvapaschoal.pdf: 9955630 bytes, checksum: a25cace9c9785b91c273376bf940d222 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-17T13:42:19Z (GMT) No. of bitstreams: 1 diegofernandodasilvapaschoal.pdf: 9955630 bytes, checksum: a25cace9c9785b91c273376bf940d222 (MD5) / Made available in DSpace on 2017-05-17T13:42:19Z (GMT). No. of bitstreams: 1 diegofernandodasilvapaschoal.pdf: 9955630 bytes, checksum: a25cace9c9785b91c273376bf940d222 (MD5) Previous issue date: 2014-08-26 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Um estudo sistemático a respeito da importância do nível de teoria e do conjunto de funções de base no cálculo de propriedades moleculares foi conduzido. Foram realizados estudos a respeito das propriedades ópticas lineares (OL) e não-lineares (ONL) de moléculas diatômicas, pequenas moléculas poliatômicas e moléculas orgânicas conjugadas com grupos doadores e retiradores de elétrons. Além disso, foi avaliada a estrutura e reatividade de complexos de Pt(II) e Pd(II). Por fim, um estudo a respeito do deslocamento químico de 195Pt foi conduzido, onde diversos parâmetros que influenciam em tal propriedade foram extensivamente analisados. Para cada trabalho proposto um novo conjunto de funções de base foi desenvolvido. Foram propostas as bases D10 (BH), P3 (CO), F3 (CS), J5 (N2), NLO (H,C,N,O,F,S), NLO-X (X=I,II,III,V,aV) (H,B-F,Si-Cl), mDZP (Pd,Pt), kPd-ADZP(Pd) e NMR-TZPP-DKH (H-He, Li-Ne, Na-Ar, K-Ca, Ga-Kr, Rb-Sr, In-Xe e Pt). Previsões das propriedades OL e ONL de diversas moléculas foram realizadas. Para um conjunto de moléculas com valores de primeira hiperpolarizabilidade (β) variando de 0 a 190 esu um desvio médio absoluto de 13,2 esu foi encontrado no nível cam-B3LYP/NLO-V em comparação com um desvio de 27,2 esu com a base da literatura 6-31G(2d). Além disso, foram realizados estudos de estrutura e reatividade da cisplatina e do cispaládio. Para a reação de hidrólise da cDDPt foi prevista uma barreira de energia no nível B3LYP/mDZP/6-31+G(d) de 22,8 kcal.mol-1 que está em excelente acordo com o valor experimental de 22,±0,4 kcal.mol-1. Considerando a mesma reação, porém para o análogo de Pd, um valor de 17,11 kcal.mol-1 no nível B3LYP/mDZP/6-31+G(d) e de 16,94 kcal.mol-1 no nível B3LYP/kPd-ADZP/6-31+G(d) foram previstos e estão em bom acordo com o valor esperado de 16,34 kcal.mol-1. Somado a isso, uma análise a respeito do deslocamento químico de 195Pt foi abordada, onde para uma ampla faixa de 73 complexos de Pt(II) um desvio absoluto médio de apenas 156 ppm foi encontrado no nível GIAO-B3LYP(DKHSO)/NMR-TZPP-DKH/IEFPCM-UFF. Todas as bases aqui propostas foram testadas de forma sistemática e, no geral, bons resultados foram encontrados para as propriedades analisadas e com custos computacionais altamente acessíveis. / A systematic study about the importance of the level of theory and the basis sets in the calculation of molecular properties was conducted. It performed studies on the linear and nonlinear optical properties of diatomic molecules, small polyatomic molecules and conjugated donor/acceptor organic molecules. In addition, the structure and reactivity of Pt(II) and Pd(II) complexes were evaluated. Finally, a study about the 195Pt chemical shift was conducted, where various parameters that influence such property have been extensively analyzed. For each work proposed a new basis set was developed. The following basis sets were proposed: D10 (BH), P3 (CO), F3 (CS), J5 (N2), NLO (H,C,N,O,F,S), NLO-X (X=I,II,III,V,aV) (H,B-F,Si-Cl), mDZP (Pd,Pt), kPd-ADZP(Pd) and NMR-TZPP-DKH (H-He, Li-Ne, Na-Ar, K-Ca, Ga-Kr, Rb-Sr, In-Xe e Pt). Estimates of L-NLO properties of several molecules were performed. For a set of molecules with values of first hyperpolarizability (β) ranging from 0 to 190 esu, an average absolute deviation of 13,2 esu was found at cam-B3LYP/NLO-V level compared with 27,2 esu with the standard basis set 6-31G(2d). Furthermore, studies of structure and reactivity of cisplatin and cispalladium were performed. For the aquation reaction of cisplatin an energy barrier of 22.8 kcal.mol-1 was predicted at B3LYP/mDZP/6-31+G(d) level, which it is in excellent agreement with the experimental value of 22.9±0.4 kcal.mol-1. Considering the same reaction, but for Pd analogous, a value of 17.11 kcal.mol-1 at B3LYP/mDZP/6-31+G(d) level and 16.94 kcal.mol-1 at B3LYP/kPd-ADZP/6-31+G(d) level were predicted and these values are in good agreement with the expected value of 16.34 kcal.mol-1. Added to this, an analysis about the 195Pt chemical shift was addressed, where for a wide range of 73 Pt(II) complexes and average absolute deviation of only 156 ppm was found at GIAO-B3LYP(DKHSO)/NMR-TZPP-DKH/IEFPCM-UFF level. All basis sets proposed here were systematically tested and, in general, good results were found for the properties of interest and highly affordable computational costs.

Ο όρος μη γραμμική οπτική (nonlinear optics) αναφέρεται στον κλάδο της φυσικής που μελετά τις μεταβολές που επέρχονται στις οπτικές ιδιότητες της ύλης, όταν αυτή αλληλεπιδρά με ισχυρά ηλεκτρομαγνητικά πεδία. Οι δέσμες λέιζερ (laser) αποτελούν το κατ’ εξοχήν ηλεκτρομαγνητικό πεδίο που χρησιμοποιείται για να προκαλέσει τη μη γραμμική οπτική απόκριση της ύλης, λόγω της ισχυρής ακτινοβολίας. Με την ανακάλυψη του λέιζερ τη δεκαετία του 1960, παράλληλα αναπτύχθηκαν πολλές τεχνικές μέσω των οποίων καθίσταται εφικτός ο προσδιορισμός της μη γραμμικής οπτικής απόκρισης των υλικών. Κίνητρο για αυτή την εκτεταμένη έρευνα αποτελεί το γεγονός ότι υλικά με σημαντική μη γραμμική απόκριση βρίσκουν πολλές εφαρμογές στη φωτονική και την οπτοηλεκτρονική. Ειδικότερα, τέτοια υλικά μπορούν να χρησιμοποιηθούν ως οπτικοί περιοριστές (optical limiters) για την προστασία από υψηλές δέσμες λέιζερ, ως οπτικοί διακόπτες (optical switches), καθώς και ως οπτικές λογικές πύλες (optical logic gates) κ.α. Τα τελευταία χρόνια υπάρχει ιδιαίτερο ερευνητικό ενδιαφέρον στο πεδίο των μοριακών διακοπτών (molecular switches). Ο όρος μοριακός διακόπτης αναφέρεται στην δυνατότητα ύπαρξης ενός μορίου μεταξύ δύο διαφορετικών καταστάσεων, ικανότητα που θα αποτελέσει την αφετηρία για μια λειτουργία “on/off”, σε μοριακό επίπεδο. Υποψήφια μόρια που μπορούν να υποστηρίξουν μια διακοπτική λειτουργία είναι εκείνα που παρουσιάζουν κάτω από ορισμένες συνθήκες αλλαγή σε μια εγγενή ιδιότητά τους, όπως ο φθορισμός, η αγωγιμότητα, η μαγνήτιση, ο στερεο-ισομερισμός, η μη γραμμικότητα κ.α. Σκοπός της παρούσας ειδικής ερευνητικής εργασίας ήταν ο προσδιορισμός της τρίτης τάξης μη γραμμικής οπτικής απόκρισης μοριακών συστημάτων που περιέχουν αζοβενζόλιο, υπό μορφή διαλυμάτων. Τα μόρια αυτά είναι ενδιαφέροντα γιατί αφ’ ενός εμφανίζουν trans/cis ισομερισμό, αφ’ ετέρου παρουσιάζουν μια αλλαγή στη μη γραμμικότητά τους εξαιτίας του φωτο-ισομερισμού του διπλού δεσμού –N=N-. Η δομή της εργασίας έχει ως εξής : Στο πρώτο κεφάλαιο θα γίνει μια περιγραφή της μη γραμμικής αλληλεπίδρασης ύλης-πεδίου, η εξαγωγή της μη γραμμικής κυματικής εξίσωσης, καθώς επίσης και μερικών φυσικών διαδικασιών που περιγράφονται μέσω αυτής. Στο δεύτερο κεφάλαιο θα περιγραφεί η πειραματική τεχνική που ακολουθήθηκε, θα αναφερθούν οι οπτικές παράμετροι που σχετίζονται με τη τρίτης τάξης μη γραμμικότητα και τέλος θα περιγραφεί η διαδικασία ανάλυσης των πειραματικών αποτελεσμάτων. Στο τρίτο κεφάλαιο θα γίνει μια σύντομη περιγραφή της πειραματικής διάταξης καθώς και των κυριότερων οργάνων που την αποτελούν. Στο τέταρτο κεφάλαιο θα παρουσιασθούν τα πειραματικά αποτελέσματα που προέκυψαν από την εργασία. Αρχικά παρουσιάζεται μια σύντομη περιγραφή των μοριακών συστημάτων που μελετήθηκαν. Ακολουθεί η μη γραμμική οπτική απόκριση των συστημάτων για διέγερση με παλμούς χρονικής διάρκειας 35 ps, στα 532 και 1064 nm,και ακολουθεί ο προσδιορισμός της μη μεταβατικής μη γραμμικής απόκρισης για διέγερση με παλμούς διάρκειας 4 ns. Αναφέρονται τα συμπεράσματα από τη μελέτη των συστημάτων και ακολουθεί μια πρόταση για μελλοντική μελέτη. / Extensive research in the field of molecular switches promises a wide variety of switching mechanisms characterized by an eclectic range of intrinsic properties regarding their luminescence, conductivity, magnetic and optical outputs. Because of their controlled alternating properties and the ease of their preparation and modification, molecular switches hold the promise of becoming pivotal components of organic–integrated photonic devices. Among the many available systems, azobenzene dyes represent a particularly promising class of organic switchable materials. The advantage of azobenzene chromophores as molecular switches is based not only on the large geometrical change accompanying the cis–trans isomerization, but also on their photo–stability, and the ease of their preparation and derivatization. In addition, azobenzene chromophores, exhibiting in general large nonlinear optical response, are characterized by an important change in their third-order nonlinear optical response due to the photo-isomerization of the –N=N- double bond. The purpose of this work is hence to describe how the NLO properties of the azobenzene are influenced when surrounded by an always more electron-donating and conjugated environment. In order to do so, we are studying three azobenzene-centered molecules. In two of them, the switch is bonded to two electron-rich groups such as alkylated anilines via either one or two ethynil spacers. In the latter, a Zn-porphyrin was instead linked to the aza-core. The insertion of a porphyrin core was driven by its high polarizability and optical oscillator strength which gives the material remarkable NLO behavior, making it potentially useful for ultra-fast switching technologies. In that view, the nonlinear optical response of these novel azobenzene based molecules dissolved in dichloromethane are studied by means of Z-scan technique using 35 ps laser pulses at 532 and 1064 nm. From the measurements, the nonlinear absorption and refraction and the corresponding third-order susceptibility χ(3) and second hyperpolarizability are determined.

Cette thèse traite du contrôle et de la caractérisation de l'alignement et de l'orientation du point de vue théorique et expérimental. L'alignement d'une molécule linéaire consiste à obtenir une probabilité élevée de localisation de l'axe internucléaire symétrique autour de l'axe de polarisation du champ tandis que l'orientation privilégie un sens particulier le long du champ. L'orientation à l'aide d'impulsions bi couleur (2+1) non résonnantes est étudiée en détail et les conditions permettant d'obtenir une orientation efficace sont examinées. Un schéma bi couleur où la deuxième harmonique est en quasi-résonance avec un niveau vibrationnel de la molécule est également étudié. Cette technique présente l'avantage d'offrir un paramètre supplémentaire à savoir l'écart à la résonance qui peut être ajusté de manière à optimiser l'orientation moléculaire. Finalement une nouvelle technique expérimentale de détection de l'alignement moléculaire est présentée. Celle-ci permet une détection monocoup de l'alignement moléculaire sur une étendue temporelle jusqu'alors inégalée. / This thesis is about the control and characterisation of the alignment and orientation of molecules by ultra short laser pulses on a theoretical and experimental approach. Alignment corresponds to a symmetric angular distribution of the molecular axis peaked along the laser field axis, whereas orientation provides an asymmetric distribution favouring one spatial direction. Orientation by sudden two-colour (2+1) pulses is studied extensively for the non resonant case and conditions required for achieving significant orientation are explored. A second two-colour scheme, where the second harmonic is in quasi resonance with a vibrational level of the molecule, is also presented and discussed. The last technique has the advantage to offer the detuning of the laser frequency as an additional free parameter, which can be adjusted to enhance molecular orientation. A new experimental polarization imaging 2D technique for the detection alignment is also developed. Experimental results on single shot detection of molecular alignment achieved over an unprecedented temporal span are presented.

In der vorliegenden Arbeit werden die nichtlinearen optischen Eigenschaften der Materialien Lithiumniobat und Di-Zinn-Hexathiohypodiphosphat aufgrund der Suszeptibilität 3. Ordnung und kleiner Polaronen untersucht. Zudem wird gezeigt, dass die Interferenz verschiedenfarbiger Laserpulse die Aufzeichnung von statischen und dynamischen holographischen Gittern ermöglicht. Ein Teil dieser Arbeit ist in den im Anhang angegebenen 6 Publikationen bereits veröffentlicht. Lithiumniobat wird mit einer Erweiterung des Z-Scan Experiments untersucht, welches die Pulslängenabhängige Messung der nichtlinearen Absorption und der nichtlinearen Brechungsindexänderung ermöglicht. Dabei konnte festgestellt werden, dass bei sehr kurzen Pulslängen von 70 fs ein Effekt der Polaronen auf die nichtlineare Absorption vernachlässigbar ist und die Zwei-Photonen-Absorption die nichtlineare Absorption dominiert. Mit größerer Pulslänge gibt es allerdings Abweichungen zwischen der Theorie der Zwei-Photonen-Absorption und den Messergebnissen. Mit der Entwicklung eines Polaronen-Anregungs-Modells, welches eine polaronische Absorption aufgrund wiederholtem optisch induziertem Hopping annimmt, konnte dieser Effekt konsistent erklärt werden. Die Messungen der nichtlinearen Brechungsindexänderung lassen darauf schließen, dass sowohl freie Ladungsträger als auch kleine Polaronen neben der Suszeptibilität 3. Ordnung einen Einfluss auf die Brechungsindexänderung haben, da eine nichtlineare Abhängigkeit von der Intensität auch bei Pulslängen von 70 fs festgestellt werden konnte. Analog dazu konnte in Di-Zinn-Hexathiohypodiphosphat ein großer Zwei-Photonen-Absorptionskoeffizient festgestellt werden, welcher für Photonenenergien nahe der Bandkante Werte zeigt, die größer sind als theoretischen Überlegungen zeigen. Eine transiente Absorption nach optischer Anregung, gemessen durch ein Anreg-Abtast-Experiment, sowie Literatur legen nahe, dass in Di-Zinn-Hexathiohypodiphosphat gebundene Lochpolaronen durch optische Anregung entstehen können. Durch den hohen Zwei-Photonen-Absorptionskoeffizienten konnte das Aufzeichnen eines kontrastreichen, dynamischen Amplitudengitters mittels Femtosekundenpulsen gezeigt und nachgewiesen werden. Die Kürze der Femtosekundenpulse ermöglicht aber nicht nur das Aufzeichnen eines Zwei-Photonen-Absorptionsgitters aufgrund der hohen Intensitäten, sondern erlaubt zudem die Beobachtung von Interferenz zwischen verschiedenfarbigen Pulsen. In der Zeitspanne der Pulslänge beträgt die Bewegung der Interferenzstreifen, welche in der Größenordnung der Lichtgeschwindigkeit liegt, nur ein Bruchteil der Streifendistanz, sodass das Interferenzmuster eingefroren und beobachtbar erscheint. Somit lassen sich statische Hologramme in holographischen Filmen, wie auch dynamische Hologramme aufzeichnen. Über ein dynamisches holographisches Gitter mittels Zwei-Photonen-Absorption konnte so eine Frequenzkonversion durch Dopplerverschiebung in Lithiumniobat gezeigt werden.