Photophysics solvent effects

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

Catalan J, Perez P, Laynez J, Garcia-Bianco F (1991) Analysis of the solvent effect on the photophysics properties of 6-propionyl-2-(dimethylamino)naphthalene (PRODAN). J Fluor-esc 4 215-223... 

The analysis of the transient fluorescence spectra of polar molecules in polar solvents that was outlined in Section I.A assumes that the specific probe molecule has certain ideal properties. The probe should not be strongly polarizable. Probe/solvent interactions involving specific effects, such as hydrogen-bonding should be avoided because specific solute/solvent effects may lead to photophysically discrete probe/solvent complexes. Discrete probe/solvent interactions are inconsistent with the continuum picture inherent in the theoretical formalism. Probes should not possess low lying, upper excited states which could interact with the first-excited state during the solvation processes. In addition, the probe should not possess more than one thermally accessible isomer of the excited state. 

An Example The Phosphorescence of Dithiosuccinimide Many thio-carbonyls have photostable excited (n > ji ) and (ti —> ti ) states that tend to relax by photophysical rather than photochemical processes.177,178 Recently, the electronic spectra of dithioimides have been under experimental and theoretical investigation.179-181 The spin-forbidden radiative decay of the lowest-lying triplet state of dithiosuccinimide may serve as an example to illustrate the results of the previous sections. Experimentally a lifetime of 0.10 0.01 ms was determined for the Ti state.179 This value has been corrected for solvent effects, but the transition may include radiative as well as nonradiative depletion mechanisms. 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

In order to study solvent effects on the excited state photophysical properties and nonradiative decay of uracil, additional na-AIMD simulations of uracil in liquid water have been carried out [64], Figure 10-7 shows the periodic simulation cell containing uracil and 39 water molecules. We have verified that at any time in... 

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

Detailed analyses of intramolecular structures are possible. Comparison of NMR and fluorescence data shows meso- and racemic diastereoisomers are found from 2,4-di(2-pyrenyl)pentane 24 jhe polarization of monomer and excimer of 4,9, disubstituted pyrenes have been measured in nematic liquid crystals 25 Quenching of pyrene fluorescence by alcohols in cyclodextrin inclusion complexes has also been studied in detail 26 Solvent effects on the photophysical properties of pyrene-3-carboxylic acid has been used to measure the pJJ, in different solvents 27 Geminate recombination in excited state proton transfer reactions has been studied with... 

Solvent reorientation and isomerization of trans-stilbene in alkane solutions has been studied by ps time scale anisotropic absorption and polarization239 Coupling of solute and solvent decreases as the size of the solvent molecules increases. The applicability of currently favoured models for the activated barrier crossing in the photoisomerization of stilbene is discussed, A method for measuring quantum yields in the photoisomerization of trans-stilbene gives high accuracy without use of a chemical actinometer . Evidence has been found for dynamic solvent effects on the photoisomerization of 4,4 -dimethoxystilbene in which the effects of temperature and hydrostatic pressure were made in n-alkane and n-alkyl alcohol. A ps laser time-resolved study fits frequency dependent solvent shifts but gives results inconsistent with the free volume model. Photophysical and theoretical studies of trans and 9-... 

R. S. Becker, C. Lenoble, and A. Zein, Photophysics and photochemistry ofthe nitro derivatives of salicylideneaniline and 2-(2 -hydroxyphenyl)benzothiazole and solvent effects, J. Phys. Chem. 91, 3517-3524(1987). 

A detailed study of the photophysics and photochemistry of 2,2-diphenyl-hexamethyltrisilane (73) (Scheme 7) has been made. In polar solvents (73) exhibits an intense fluorescence attributed to intramolecular charge transfer, and this solvent effect is also reflected in the photochemistry. In non-polar solvents extrusion of diphenylsilylene and 1,3-silyl migration to give (74) are the major photoreactions but in ethanol-hexane solvolytic cleavage of the... 

Absorption and fluorescence spectra of 7-aminocoumarin derivatives have been recorded and the photophysics of coumarin inclusion complexes with 0- and y-cyclodextrins investigated. Solvent effects on the photophysical behaviour of pyrrolocoumarin derivatives are similar to those on the psorolens . Vibronic exciton bands and the absorption spectra of Eosin Y dimers have been analysed theoretically and compared with experimental data. Picosecond spectroscopic studies have been made on the ionic photodissociation dynamics of malachite green leucocyanide . The lowest state produces ions within 0.1 to 0.5 ns whilst for higher states 6-13 ps are sufficient for the development of charge separation. The photophysics of crystal violet in a series of n-... 

The electron donor-acceptor molecular complexes between iodine and thiazole, benzothiazole, and some derivatives have been studied in several organic solvents by UV spectroscopy <87CJC468>. In all cases, the presence of the thiazole ring produces a displacement of the Amax iodine band at 512 nm towards shorter wavelengths and a decrease of its absorbance. Moreover, a sharp isosbestic point near 470 nm was observed for all iodine-thiazole complexes. 2-Aryl and 2-hetarylbenzothiazoles showed fluorescence, the maxima of emission being between 350 nm and 395 nm. Both substituent and solvent effects on the spectra were observed <93MI 306-02>. The photophysical properties of bis(benzothiazolylidene)squaraine dyes have also been studied <93JPC13625>. 

Jones G, Jackson WR, Kanoktanapom S, Halpem AM. Solvent effects on photophysical parametas for coumarin laser dyes. OptCommun 1980 33 315-20. 

Theoretical calculations on the nature of solvent effects which affect the n-Jt blue shifts for pyrimidine, pyridazine, and pyrazine have been compared with the results of experimental observation . A theoretical study of electronic spectra and photophysics of uracil derivatives , the luminescence of 4-phenylpyridine and... 

A theoretical paper discusses the nature of solvent effects which affect the deactivation of A 02 . The effect of hydrostatic pressure on the radiationless deactivation of 03 in solution has also been reported . The perturbing effects of the solvents H2O, DjO, and QH5CH3 on the luminescence rate constant of O2 up to 100 atm provide evidence for pardcipation of complexes involving both the ground and excited states of molecular oxygen . The application of a collision complex model has been applied to the interpretation of photophysical quenching of 03 in liquids by 4-amino-TEMPO . 

Fung, S. Y, Duhamel, J., Chen, P. (2006). Solvent effect on the photophysical properties of the anticancer agent eUipticine. J. Phys. Chem. 110 (40), 11446-11454. 

Victor Akpe, Hjalmar Brismar, Tebello Nyokong, Osadebe, P. O. Photophysical and photochemical parameters of octakis (benzylthio)phthalocyaninato zinc, aluminum and tin Red shift index concept in solvent effect on the ground state absorption of zinc phtha-locyanine derivatives. 

The use of a single parameter (e.g., E(A) or E(F) or any other photophysical parameter) to describe solvent polarity is based on the assnmption that it is necessary to take only one mechanism of solute-solvent interaction into acconnt. The inadequacy of the dielectric model of solvent to represent the solvent effect on the varions properties of solutes aud proliferation of empirical polarity scales point to the existence of specific solute-solvent interaction. According to Equation 7.1 any solvent-dependent property (A) of a solute 5" in a solvent T can be represented as... 

JB Birks. Photophysics of Aromatic Molecules. London Wiley-Interscience, 1970. A Nakajima. Solvent effect on the vibrational structures of the fluorescence and absorption spectra of pyrene. Bull Chem Soc Jpn 44 3272, 1971. 

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