La structure et la spectroscopie de molécules d'intérêt astrophysique ont été étudiées par des méthodes de calcul électronique ab initio hautement corrélées. Notre démarche a tout d'abord été d'étudier des systèmes allant de deux à quatre atomes, afin de voir l'influence du niveau de calcul électronique utilisé lors de la détermination de données comparables aux résultats expérimentaux. Ainsi, l'étude de la spectroscopie des états électroniques de la molécule AlCl a été entreprise. Les résultats obtenus pour ce système reproduisent parfaitement les mesures expérimentales existantes tout en introduisant la compréhension des phénomènes observés. Nous avons ensuite prédit un ensemble de données pour les ions AlCl+ et AlCl2+, en utilisant la même méthodologie. Nous avons également entrepris des calculs de durée de vie de prédissociation pour les molécules SH et SH+. Nos courbes d'énergie potentielle hautement corrélée nous ont permis de reproduire avec une grande précision les durées de vie de prédissociation des niveaux rovibrationnels de SH. Par la suite, nous avons étudié une molécule d'intérêt astrophysique, détectée dans l'atmosphère de Titan, N2H+. Nous avons généré des surfaces d'énergie potentielle multidimensionnelles pour les états fondamentaux des molécules N2H+, N2H2+ et N2HAr+. Ces surfaces ont été utilisées pour le calcul des niveaux rovibrationnels de ces ions et de leurs espèces deutérées. Un excellent accord avec les donné es expérimentales disponibles a été obtenu, et un ensemble de constantes spectroscopiques a été prédit. Enfin, nous nous sommes intéressés à une molécule plus grande, Si(C2H3)4. Cette étude nous a permis d'établir une méthodologie pour le calcul de la structure et des états électroniques excités de molécules de taille moyenne. Nous avons également effectué des calculs sur l'ion Si(C2H3)4+, afin d'interpréter sa fragmentation mesurée lors de l'expérience d'impact d'électron réalisée à l'Université de Bratislava durant cette thèse / Highly correlated ab initio methodologies were used to investigate the structure and the spectroscopy of small and medium sized molecules at different levels of theory. Our results are compared to the available experimental data. For the AlCl molecule, our computed spectroscopic constants were in good agreement with the experimental ones, allowing us to predict a set of predictive data for the less known AlCl+ and AlCl2+ ions. After that, we treated the predissociation lifetimes of the A state of SH and SH+. Our highly correlated calculations allowed us to reproduce the lifetimes measured experimentally. Thereafter, multidimensional potential energy surfaces of the ground state of N2H+, N2H2+ and N2HAr+ were generated. These surfaces were used for the calculations of rovibrational levels of these ions and their respective deuterated species. An overall excellent agreement was obtained comparing to the available experimental measurements. Finall y, we investigated the Si(C2H3)4 molecule in order to establish a methodology for the treatment of the structure and electronic excited states of medium sized molecules. We also studied the reactivity of the Si(C2H3)4+ ion for a tentative assignment of the mass spectra obtained in the University of Bratislava by an electron impact experiment

<p>Two-photon excited fluorescence microscopy (TPM) has become a standard biological imaging tool due to its simplicity and versatility. The fundamental contrast mechanism is derived from fluorescence of intrinsic or extrinsic markers via simultaneous two-photon absorption which provides inherent optical sectioning capabilities. The NIR-II wavelength window (1000–1350 nm), a new biological imaging window, is promising for TPM because tissue components scatter and absorb less at longer wavelengths, resulting in deeper imaging depths and better contrasts, compared to the conventional NIR-I imaging window (700–1000 nm). However, the further enhancement of TPM has been hindered by a lack of good two-photon fluorescent imaging markers in the NIR-II. </p><p>In this dissertation, we design and characterize novel two-photon imaging markers, optimized for NIR-II excitation. More specifically, the work in this dissertation includes the investigation of two-photon excited fluorescence of various highly conjugated porphyrin arrays in the NIR-II excitation window and the utilization of nanoscale polymersomes that disperse these highly conjugated porphyrin arrays in their hydrophobic layer in aqueous environment. The NIR-emissive polymersomes, highly conjugated porphyrins-dispersed polymersomes, possess superb two-photon excited brightness. The synthetic nature of polymersomes enables us to formulate fully biodegradable, non-toxic and surface-functionalized polymersomes of varying diameters, making them a promising and fully customizable multimodal diagnostic nano-structured soft-material for deep tissue imaging at high resolutions. We demonstrated key proof-of-principle experiments using NIR-emissive polymersomes for in vivo two-photon excited fluorescence imaging in mice, allowing visualization of blood vessel structure and identification of localized tumor tissue. In addition to spectroscopic characterization of the two-photon imaging agents and their imaging capabilities/applications, the effect of the laser setup (e.g., repetition rate of the laser, peak intensity, system geometry) on two-photon excited fluorescence measurements is explored to accurately measure two-photon absorption (TPA) cross-sections. A simple pulse train shaping technique is demonstrated to separate pure nonlinear processes from linear background signals, which hinders accurate quantification of TPA cross-sections.</p> / Dissertation

Ultra-violet and visible light induced processes in small organic molecules play very important roles in many fields, e.g., environmental sciences, biology, material development, chemistry, astrophysics and many others. Thus it is of great importance to better understand the mechanisms behind these processes. To achieve this, a bottom-up approach is most effective, where the photo-induced dynamics occurring in the simplest organic molecule (ethylene) are used as a starting point. Simple substituents and functional groups are added in a controlled manner to ethylene, and changes in the dynamics are investigated as a function of these modifications. In this manner, the dynamics occurring in more complex systems can be explored from a known base. In this thesis, the excited state dynamics of small organic molecules are studied by a combination of time-resolved photoelectron spectroscopy and various computational methods in order to determine the basic rules necessary to help understand and predict the dynamics of photo-induced processes. The dynamics occurring in ethylene involve a double bond torsion on the ππ* excited state, followed by the decay to the ground state coupled with pyramidalization and hydrogen migration. Several different routes of chemical modification are used as the basis to probe these dynamics as the molecular complexity is increased. (i) When ethylene is modified by the addition of an alkoxyl group (-OCnH2n+1), a new bond cleavage reaction is observed on the πσ* state. When modified by a cyano (-CN) group, a significant change in the carbon atom involved in pyramidalization is observed. (ii) When ethylene used to build up small cyclic polyenes, it is observed that the motifs of the ethylene dynamics persist, expressed as ring puckering and ring opening. (iii) In small heteroaromatic systems, i.e., an aromatic ring containing an ethylene-like sub-structure and one or two non-carbon atoms, the type of heteroatom (N: pyrrole, pyrazole O: furan) gives rise to different bond cleavage and ring puckering channels. Furthermore, adding an aldehyde group (-C=O) onto furan, as a way to lengthen the delocalised ring electron system, opens up additional reaction channels via a nπ* state. The results presented here are used to build up a more complete picture of the dynamics that occur in small molecular systems after they are excited by a visible or UV photon, and are used as a basis to motivate further investigations. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.</p>

Les molécules se trouvent très rarement isolées, ceci implique qu'une modélisation de leur environnement doit être faite lors du calcul de propriétés physiques ou chimiques. Il est possible de considérer l'environnement par plusieurs méthodes de chimie théorique. Le modèle du continuum polarisable est un exemple dont les premières applications ont maintenant plus de 30 ans. Ce modèle permet de reproduire l'influence d'un solvant mais n'est pas capable de représenter des milieux fortement anisotropes tels que les macro-molécules. Afin de représenter de tels environnements, des méthodes couplant la mécanique quantique, pour le traitement de la partie d'intérêt chimique ou physique, et la mécanique moléculaire pour la représentation de l'environnement, ont été développées. Cette thèse est consacrée à l'étude de complexes de ruthénium en interaction avec l'ADN. Leurs spectres d'émission présentent des particularités trés intéressantes dues à cette interaction. Nous montrons que les propriétés photophysiques calculées doivent prendre en compte l'environnement. En particulier, nous avons utilisé une méthode permettant de modéliser la réponse électronique de l'environnement lors de transitions électroniques verticales. Les états triplets de ces complexes intercalés entre deux paires de bases de l'ADN sont également étudiés. En effet, les propriétés d'émission sont liées à la nature de ces derniers et il est important de modéliser de façon correcte le double-brin pour comprendre les mécanismes mis en jeu. Nous avons ainsi donné une interprétation physique à l'effet light-switch / Molecules are rarely isolated and a modelisation of their environment must be carried out when computing their physical or chimical properties. Quantum chemistry offers various ways to take into account this environment. For instance, polarizable continuum model is available for more than 30 years. This model is able to reproduce the influence of a solvent upon a solute but while the environment is becoming less isotropic, serious limitations are found for the model. In order to represent such environments, methods coupling quantum mechanics, for the treatment of the physically or chemically interesting part, and molecular mechanics for the environment have been developped. This thesis is dedicated to the study of ruthenium complexes in interaction with DNA. Moreover, their emission spectra are strongly modified by this interaction. We show that the photophysical properties calculated must take into account the environment. Eventually, we used a methodology able to include effects linked to the electronic response of the surroundings when computing vertical transitions. Triplets of these complexes intercalated between 2 DNA base pairs are also studied. Indeed, emission properties are linked to the nature of these and it is necessary to modelize correctly the double-strand to better understand mecanisms involved. The light-switch effect is then elucidated

Dans cette thèse, nous nous intéressons à la monotonie de la vitesse de la marche aléatoire excitée (MAE) avec biais $bein[0,1]$ dans la première direction $e_1$. Nous présentons une nouvelle preuve de la monotonie de la vitesse pour des grandes dimensions $dgeq d_0$ et pour le cas où le paramètre $be$ est petit quand $dgeq 8$. Ensuite, nous considérons les marches aléatoires avec plusieurs cookies aléatoires. La monotonie de la vitesse est ausi prouvée pour les cas particuliers par exemple des dimensions sont grandes, le paramètre de dérive $be$ est petit ou le nombre de cookies est grand. Ce sont les cas où la marche aléatoire est proche à la marche aléatoire simple. Pour l'existence de la vitesse, nous avons montré la loi des grands nombres pour un cas particulier du cookie aléatoire stationaire, mais nous n'arrivons pas encore pour le cas stationaire. Sur la monotonie, nous avons aussi vérifié que le nombre de points visités par la marche aléatoire simple avec biais $be$ est croissant.Finalement, une question très interessant: la monotonie de la vitesse, est-elle vraie pour la MAE pour les petites dimensions $2leq dleq 8.$ Pour cette motivation, nous avons prouvé que la vitesse est indéfiniment différentiable pour $be>0.$ Au point critique $0$, nous avons prouvé que la dérivée de la vitesse existe et égale $0$ pour $d=2$, existe et est positive pour $dgeq 4.$ Mais nous ne savons pas encore si la dérivée de l'ordre 2 en point $0$ existe ou au moin la dérivée est continue en $0$ pour prouver la monotonie de la vitesse au voisinage de $0$? / In this thesis, we are interested in the monotonicity of the speed of the excited random walk (ERW) with bias $bein[0,1]$ in the first direction $e_1.$ The speed is defined as the limit obtained by the law of large number for the horizontal component. The speed depend on the bias $be.$ We present a new proof of the monotonicity of the speed for the dimension $dgeq d_0$, where $d_0$ is large enough, or for the parameter $be$ is small when $dgeq 8$. After that, we consider the random walk with multi-random cookies. The monotonicity of the speed is also proved for some particular cas, for exemple when the dimension is high, or the parameter drift is small, or the number of cookies is large. These are the cas where the walk is near the simple random walk. For the existence of the speed, we also proved the law of large number for a particular cas of stationary cookie but we haven't yet gotten the cas stationary. On the monotonicity, we also proved the rang of the simple random walk with drift $be$ is increasing in the drift. Finally, a question very interesting: the monotonicity of the speed of ERW is true for the small dimension $2leq dleq 8$, isn't it? For this motivation, we proved the speed is infinitly differentiable for all $be>0.$ At the critical point $0,$ we also proved the derivative of the speed at $0$ exists and equals $0$ for $d=2$, exists and is positive for $dgeq 4.$ But we haven't yet known if the derivative of order $2$ at $0$ exists or at least the derivative is continuous at $0$ to prove the monotonicity of the speed in a neighbor of $0$.

Nous proposons de développer une méthodologie théorique pour étudier l’influence de stimuli externes sur les cristaux organiques. On s’intéresse en particulier au mécanochromisme, aggregation-induced emission, et le transfet des protons. Ces phénomènes, récemment observés expérimentalement, sont encore mal compris et il n’existe pas à l’heure actuelle de méthodologie bien définie pour les comprendre. Cette thèse développera les outils de modélisation des couplages des propriétés optiques aux phénomènes d’aggregation, réactivité et de déformation á l'etat solide. / To develop a theoretical methodology to study the influence of external stimuli on fluorescent crystals. We are particularly interested in excited state reactivity, aggregation-enhanced fluorescence and responses to mechanical stimuli. Such phenomena are often not yet understood at a molecular level, a problem exacerbated by the absence of adequate and cost-efficient computational models. This thesis counters this problem by developing a method capable of describing the solid state environment in the context of excited-state calculations at the quantum level.

Peroxidase de rábano (\"horseradish peroxidase - HRP), atuando como uma oxidase frente a substratos apropriados, catalisa a formação de espécies eletronicamente excitadas triplete. Os produtos obtidos são os esperados da clivagem de um intermediário 1,2-dioxetânico hipotético. Espécies tripletes geradas enzimaticamente são capazes de transferir energia a vários aceptores incluindo macromoléculas tais como: fitocromo, RNA, DNA e proteínas, além de organelas como cloroplastos. Acompanhamos a oxidação aeróbica de aldeídos alifáticos lineares (C2-C6) catalisada pela HRP; esta reação gera o aldeído inferior (Cn-1) no estado excitado triplete e ácido fórmico. Dois aspectos principais são abordados neste trabalho: (i) análise dos resultados em base ao comprimento da cadeia carbônica do substrato (C2 &#8594; C6) e (ii) a procura de emissões sensitizadas em estruturas biológicas (cloroplastos e microsomas). - Oxidação aeróbica dos aldeídos alifáticos lineares C2-C6 catalisada pela HRP. Corantes xantênicos e clorofila a solubilizada em micelas foram utilizados para monitorar estados eletronicamente excitadas geradas pela oxidação aeróbica dos aldeídos alifáticos lineares catalisada pela HRP. Quando eosina é o aceptor fluorescente, máxima emissão ocorre com butanal. Este resultado é discutido em conecçao com o fato de que uma série de efeitos biológicos de ácidos alifáticos lineares são máximos com o ácido butírico. A possível paticipação de estados excitados no processo que desencadeia as atividades biológicas deste ácido é sugerida. - TransferêncIa de energia para cloroplastos. Aldeídos alifáticos lineares (C2-C6) promovem emissão em cloroplastos na região de fluorescência de clorofila. Esta habilidade deve provavelmente constituir um caso de \"luminescência escura\" (\"dark luminescence\") . Se HRP estiver presente o aldeído (Cn) é oxidado ao homólogo inferior (Cn-1) no estado triplete, o qual sensitiza direta e/ou indiretamente a fluorescência de clorofila. Clorofila excitada por este processo é incapaz de reduzir um aceptor de Hill. - Quimioluminescência de microsomas expostos à oxidação aeróbica de aldeídos lineares catalisada pela HRP. Microsomas expostos ao sistema propanal/HRP/O2 desenvolvem luminescência de baixa intensidade. Este processo emissivo é distinto daquele originário durante a peroxidação de lipídeos uma vez que: (i ) a emissão se situa próxima a 560 nm e não na região espectral do vermelho (como esperado para a emissão bimol de oxigênio singlete) e (ii) não há formação de malonaldeído. Acetaldeído triplete parecer ser a espécie responsável pela indução deste processo através da excitação de algum componente microsomal, possivelmente uma flavoproteína. / Horseradish peroxidase (HRP), acting as anoxidase upon appropriate substrates, promotes the formation of electronically excite triplet species. The products obtained are those which would be expected from the cleavage of a hypothetical 1,2 dioxetane intermediate. Enzyme-generated triplet species are able to transfer energy to several acceptors, including macromolecules such as phytochrome, RNA, DNA and proteins, as well as to organeles such as chloroplasts. In the present study, we investigated the HRP-catalyzed aerobic oxidation of linear aliphatic aldehydes (C2 to C6), a reaction which generates the next lower aldehyde in the triplet state and formic acid. Two main aspects were emphasized in this work: (i ) the dependence of the results of the length of the carbonic chain of the substrate (C2 to C6) and (ii) the possibility of inducing sensitized emission from biological structures (chloroplasts and microsomes). HRP-catalyzed aerobic oxidation of aliphatic aldehydes. Xanthene dyes and micelle-solubilized chlorophyll-a were used to monitor the electronically excited species generated by the peroxidase-catalyzed aerobic oxidation of C2-C6 linear aldehydes. Maximal emission occurs with butanal as substrate and eosine as the fluorescent acceptor. This result is discussed in connection with the fact that the multiple biological effects of short chain aliphatic acids are maximal for butyric acid. Our observations strengthen the case for a possible role of excited state formation in the biological activity butyrate. Energy transfer to chloroplasts Linear aldehydes trigger red emission from chloroplasts. If horseradish peroxidase is also present, the aldehyde is oxidized to the next lower homolog in the triplet state, which in turn sensitizes (directly or indirectly) chlorophyll fluorescence. This phenomenon probably is a case of \"dark luminescence\"; the chlorophyll excited by this process is unable to reduce a Hill acceptor. MIicrosomal luminescence elicited by enzymatic systems that generate triplet species. Microsomes exposed to the propanal/HRP/02 system develop a weak luminescence. The underlying process is distinct from that occuring during lipid peroxidation because the emission intensity peaks at around 560 nm rather than in the red (as would be expected for bimol singlet oxygen emission) and no malonaldehyde is formed. Triplet acetaldehyde appears to be responsible for initiating the process, which in turn leads to excitation of a component of microsomes, possibly a flavoprotein.

Limitadores ópticos são dispositivos que apresentam alta transmitância para baixas intensidades de luz incidente e, inversamente, baixa transmitância para altas intensidades, sendo usados como protetores contra danos em sensores ópticos e olhos humanos. Com o objetivo de estudarmos novos materiais com mecanismos não lineares eficientes para o processo de limitação, bem como novas geometrias ópticas, apresentamos neste trabalho o desenvolvimento de um limitador óptico baseado na absorção saturada reversa de porfirinas e metaloporfirinas. Construímos também um dispositivo baseado na configuração óptica bifocal, usando porfirina como absorvedor saturável reverso. Além disso, obtivemos parâmetros espectroscópicos do estado excitado pelos ajustes teóricos das curvas de transmitância, através da resolução de equações de taxa. / Optical limiters are devices with a high transmittance in the presence of low intensity light, and a considerable lower transmittance otherwise, been used as protectors against damage in optical sensors and human eyes. Aiming at searching for new materials and optical geometries efficient for optical limiting. We report on the development of an optical limiter based on the reverse saturable absorption in porphyrin and metalioporphyrins. We also built a device-based .on a cascade focus configuration, using free base porphyrin as the absorber. Besides, we obtain the excited state spectroscopy parameters by the theoretical fitting of transmittance curves, by solving a set of rate equations.

"Hydroxyl ions are a common contaminant in optical fibers, and are responsible for strong absorption centered at 1380 nm that becomes significant over long optical path lengths. Recently, however, special fabrication methods have been developed that minimize the hydroxyl ion contamination, permitting use of the entire 1300-1700 nm spectral region for telecommunications. There is therefore interest in examining the Nd 4F3/2 to 4I13/2 transition for a potential optical amplifier at 1400 nm. In this thesis, the excited state absorption cross section and the overall gain/loss spectrum of neodymium in a silica glass fiber were determined for the 1200-1500 nm wavelength region using the pump-probe method. The ground state absorption cross section was also determined from transmission measurements, and the stimulated emission cross section was calculated using the fluorescence spectrum and the McCumber relation. Oscillator strengths for absorption and emission transitions were calculated in the 800-1600 nm wavelength range using the Judd-Ofelt method. The above procedures were followed for both the Nd-doped fiber, as well as an erbium-doped silica fiber. The shape of the Nd emission spectrum is also noteworthy, since the characteristic Nd peak at 1064 nm is not observed, although there is strong emission at 1092 nm. The pump-probe measurements revealed significant excited state absorption loss between 1200 and 1350 nm, due to excitation from the 4F3/2 to the higher 4G9/2 and 4G7/2 states. Between 1350 and 1475 nm, there was no net gain or loss that could be observed beyond the level of the noise. For the glass fibers studied, it appears that in the spectral region of interest for an optical amplifier, the stimulated emission and excited state absorption cancel one another out."

Neste trabalho estudou-se a desativação de estados singlete 1&#960;,&#960;* e 1n, &#960;* através da supressão da fluorescência de antraceno e de uma série de aldeídos alifáticos. Existem alguns dados na literatura referentes à supressão da fluorescência de compostos carbonílicos alifáticos por aminas, olefinas e haletos de alquila . No caso específico da desativação de estados 1n, &#960;* de aldeídos alifáticos, alguns autores sugeriram a possibilidade de existir mais de um mecanismo envolvido no processo de supressão. Assim, delimitamos, como um dos objetivos deste trabalho, o estudo da natureza das interações envolvidas na supressão da fluorescência de aldeídos alifáticos por haletos de alquila. Foi possível determinar uma constante de supressão aparente apenas para o sistema pentanal-iodeto de etila. Verificamos que esta aparente supressão podia ser explicada por um efeito de absorção competitiva, dependente da concentração do supressor, no comprimento de onda de excitação (&#955; = 310 nm). Concluímos, também, que os dados de literatura referentes à supressão da fluorescência de cetonas por brometo de sec-butila podem ser explicados pelo tipo de purificação, inadequada, deste composto. Portanto, nossos resultados estão em das acordo com aqueles relatados para cetonas de estrutura análoga aos aldeídos estudados. De fato, concluímos que haletos de alquila não suprimem a fluorescência nem de alcanonas nem de aldeídos alifáticos. Estudou-se, também, a desativação de estados 1&#960;,&#960;* de compostos aromáticos. Embora este processo seja objeto de uma vasta gama de estudos, a natureza das interações envolvidas na estabilização do exciplex, proposto como intermediário na transferência de energia de vários processos endotérmicos, é objeto de alguma controvérsia. Neste trabalho, estudou-se a supressão de fluorescência de antraceno por sulfetos aromáticos derivados do tiofenol ou do tiocresol. As constantes experimentais de supressão foram calculadas através da equação de Stern-Volmer, utilizando-se as intensidades de fluorescência não-corrigidas. A ausência de correlação entre a cinética de supressão de fluorescência e os parâmetros de ressonância de excitação indica que este mecanismo não e o predominante na estabilização do exciplex. Por outro lado, estudando o efeito da temperatura, foi possível concluir que, a não ser para o derivado n-propílico do orto-tiocresol, não há ~ variação significativa do valor da constante de supressão, indicando que a magnitude da energia de ativação envolvida no processo de supressão é baixa. Ainda, verificamos que há correlação linear entre os parâmetros de Weller e as constantes de supressão, para todos os sulfetos, com exceção dos derivados n-propílicos que apresentam constantes de supressão maiores do que aquelas referentes a outros sulfetos de potencial de oxidação de mesma magnitude. o conjunto de dados pode ser explicado admitindo-se um processo de transferência de carga, onde o doador é o sulfeto e o aceptor é o antraceno e, no qual, a reversibilidade da formação do exciplex desempenhe um papel importante. / In this work fluorescence quenching of the 1&#960;,&#960;* states of anthracene and 1n, &#960;* states of aliphatic aldehydes was studied. There are some literature data regarding fluorescence quenching of carbonyl aliphatic compounds by amines, olefins and alkylhalides. Specifically, for aliphatic aldehydes there is the possibility that quenching occurs by more than one path. We chose as one of the objectives of this work, to understand the nature of interactions in-the deactivation of singlet excited states of aliphatic aldehydes by alkylhalides. It was possible only to determine an apparent quenching rate constant for the pentanal-ethyliodide system. This apparent quenching is due to a competitive absorption effect, at the wavelength of excitation (310 nrn) ,which is proportional to the quencher concentration. We also verified that the reported fluorescence quenching of ketones by sec-butylbromide can be due to impurities present in the halide. The results obtained in the present work totally disagree with those reported for ketones with structure analogous to the aldehydes utilized. In fact, we conclude that alkylhalide do not quench the fluorescence of either alkanones or aliphatic aldehydes. We also studied the deactivation of1&#960;,&#960;* states of aromatic compounds. Although the literature contains several studies about fluorescence quenching of aromatic compounds, the nature of the binding energy of the excited complex is the object of some controversy. In this work, we studied fluorescence quenching of anthracene by aromatic sulphides derived from thiophenol or thiocresol. Quenching constants were calculated by means of the Stern-Volmer equation, employing uncorrected fluorescence intensities. The absence of correlation between fluorescence quenching kinetics and excitation resonance parameters indicates that this mechanism does not provide the maincontribution to exciplex stabilization. On the other hand, we found that, except for the n-propyl derivative of ortho-thiocresol, there was no significant variation of quenching rate constants with temperature, which indicates a low activation energy value for this processo We verified a linear correlation between fluorescence rate constants and Weller parameters except for n-propyl derivatives, whose rate constants are greater than sulphides of the same oxidation potential. The data obtained in this study can be explained assuming formation of a charge transfer complex between anthracene and the sulphide, the first being the acceptor and the,other being the charge donnor, in which case the reversibility of the exciplex formation step must play an important role.