Solvent effects on electronic absorption spectra

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... 

Kobayashi, S., Yokoyama, H, and Kamei, H. (1987). Substituent and solvent effects on electronic absorption spectra and thermal isomerization of pull-push-substituted cis-azobenzenes. Chem, Phys. Lett. 138, 333-338. 

There is still considerable scope for systematic quantitative studies of solvent effects on electronic absorption spectra. 

Nagae, H. Theory of solvent effects on electronic absorption spectra of rodlike or disklike solute molecules frequency shifts. J. Chem. Phys. 106 (1997)... 

L. S. P. MirashiandS. S. K. xate,Spectrochimica Acta, Part A, 45(1147) (1989). Solvent Effects on Electronic Absorption Spectra of Nitrochlorobenzenes, Nitrophenols and Nitroanilines. 3. Excited State Dipole Moments and Specific Solute Solvent Interaction Energies Employing Bakhshiev Approach. 

The solvent effects on the absorption spectra of ion pairs were studied by many authors and the direction of the observed shift depends on the change (increase or decrease) of dipole moment upon the electronic transition [25]. Generally a bathochromic shift is observed with an increase of solvent polarity. When going from a polar solvent to a less polar one, the association in the ground state increases more strongly than in the excited state this may be understood if the ion pair switches progressively from SSIP to CIP status. Observations of this type were often made, together with cation effects, as for instance in the case of alkali phenolates and enolates [7], fluorenyl and other carbanion salts [22] or even for aromatic radical anions [26, 27],... 

In the light of these general effects of substitution and solvent changes on electronic absorption spectra it is to be expected that simple peptide combination will have some influence on the absorption spectra of the aromatic amino acids. These changes have been studied with simple... 

Abstract It is well known that solvents can modify the frequency and intensity of the solute spectral bands, the thermodynamics and kinetics of chemical reactions, the strength of molecular interactions or the fate of solute excited states. The theoretical study of solvent effects is quite complicated since the presence of the solvent introduces additional difficulties with respect to the smdy of analogous problems in gas phase. The mean field approximation (MFA) is used for many of the most employed solvent effect theories as it permits to reduce the computational cost associated to the smdy of processes in solution. In this chapter we revise the performance of ASEP/MD, a quanmm mechanics/molecular mechanics method developed in our laboratory that makes use of this approximation. It permits to combine state of the art calculations of the solute electron distribution with a detailed, microscopic, description of the solvent. As examples of application of the method we smdy solvent effects on the absorption spectra of some molecules involved in photoisomerization processes of biological systems. 

A consistent model permitting rationalization and prediction of the solvato-chromic behaviour of coordination compounds with MLCT absorption has been described [428]. According to this qualitative model, the changing relationship between the metal-ligand bond dipolarities in the ground and MLCT excited state determines whether the complex is negatively, positively, or not solvatochromic [428]. For comprehensive reviews on solvent effects on electronic spectra of metal complexes, see references [15, 17]. 

The term solvatochromism was introduced in 1922 by Hantzshlater [45] to explain the influence of the solvent on electronic absorption spectra. In 1951 Brooker et al. [46] suggested that the solvatochromic effect induced by a solvent on certain probes that have a strong absorption in the UV/Vis could be used as a visual indicator of the solvent polarity. One of the main reasons that spectroscopic measurements are such a popular method to obtain empirical polarity parameters is the simplicity of the experiment Electronic absorption spectroscopy is a readily available tool that requires little speciahst skill to operate. Hence, several of these scales have been used with ILs. 

N. S. Bayliss, J. Chem, Phys., 18, 292 (1950). The Effect of the Electrostatic Polarization of the Solvent on Electronic Absorption Spectra in Solution. 

An intramolecular charge transfer toward C-5 has been proposed (77) to rationalize the ultraviolet spectra observed for 2-amino-5-R-thiazoles where R is a strong electron attractor. Ultraviolet spectra of a series of 2-amino-4-p-R-phenylthiazoles (12) and 2-amino-5-p-R-phenylthiazoles (13) were recorded in alcoholic solution (73), but, reported in an article on pK studies, remained undiscussed. Solvent effects on absorption spectra of 2-acetamido and 2-aminothiazoles have been studied (92). 

Bayliss, N.S. 1950. The effect of the electrostatic polarization of the solvent on the electronic absorption spectra in solution. J. Chem. Phys. 18 292-296. 

Seliskar C, Brand L (1971) Electronic spectra of 2-aminonaphthalene-6-sulfonate and related molecules. II. Effects of solvent medium on the absorption and fluorescence spectra. JACS 93 5414-5420... 

Zeng, J., Craw, J. S., Hush, N. S. and Reimers, J. R. Solvent effects on molecular and ionic spectra. 4. Photochemistry ofFe2+(H20)6 in water revisited possible mechanisms for the primacy absorption process leading to electron ejection,/. Phys. Chem., 98 (1994), 11075-11088... 

Cyclohexadienones. The perturbation of the electronic absorption spectra by adsorption on silica gel can have a significant effect on subsequent photochemical reactions. For example, Hart has shown that 2,4-cyclo-hexadienones photochemically degrade cleanly in nonpolar solvents to a ketene (1) but in highly polar solvents or adsorbed on silica gel bicyclic ketone (2) is the predominant product.33 The absorption spectra indicate that in nonpolar solvents the lowest singlet state is the n,n state, from which the formation of the ketene proceeds. This n -n band is obscured by the band in polar media, inversion of the energy levels of the n,n, and the first... 

Spectroscopy provides a window to explain solvent effects. The solvent effects on spectroscopic properties, that is, electronic excitation, leading to absorption spectra in the nltraviolet and/or visible range, of solutes in solution are due to differences in the solvation of the gronnd and excited states of the solute. Such differences take place when there is an appreciable difference in the charge distribution in the two states, often accompanied by a profonnd change in the dipole moments. The excited state, in contrast with the transition state discussed above, is not in equilibrium with the surrounding solvent, since the time-scale for electronic excitation is too short for the readjustment of the positions of the atoms of the solute (the Franck-Condon principle) or of the orientation and position of the solvent shell around it. 

Brown, Lewis and their coworkers synthesized naphthalimide-containing TBs 94 in order to study their fluorescence properties (05TL2149). The effect of several cosolvents on the fluorescence emission is modest and under further investigation. Unlike their fluorescence spectra, the electronic absorption spectra of TBs 94 are relatively insensitive to solvent. 

Here, we summarize a recent study we have done on the effect of the environment on the electronic absorption and emission of 6-Propionyl-2-(A,A-dimethyl)aminona-phthalene (PRODAN) [8]. This system has widely been used as a fluorescence probe since it was introduced by Weber and Farris [31], The effect of polar solvents on the absorption and more effectively, on the fluorescence spectra of PRODAN is large,... 

All those spectral changes which arise from alteration of the chemical nature of the chromophore-containing molecules by the medium, such as proton or electron transfer between solvent and solute, solvent-dependent aggregation, ionization, complexation, or isomerization equilibria lie outside the scope of this chapter. Theories of solvent effects on absorption spectra assume principally that the chemical states of the isolated and solvated chromophore-containing molecules are the same and treat these effects only as a physical perturbation of the relevant molecular states of the chromophores [435-437]. 

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