The fluctuations of orientation and induction interactions in solution and their impact on the broadening of absorption and fluorescence spectra are considered in terms of a bands-of-energy model. Also covered is the application of principles of thermodynamics and self-organization of systems for calculation of solvatochromic shift, among them a component owing to the work on electronic polarization of solvent at the instant of electronic transition in the solute. The findings on solvatochromic shift and spectral broadening open the way to the calculation of solvent effects on the rate constant of nonradiative transitions. As demonstrated herein for 15 fluorophores, the novel theory of nonradiative decay of the intramolecular charge-transfer excited states is carried out for dyes and organic compounds of different nature, both for polar and nonpolar media.

The locations of the 0 0 0 -bands for S 1 ← S 0 and S 1 → S 0 transitions have been found for C 60 solutions in hexane. It is shown that the profile of the S 1 ← S 0 band is mainly shaped by h u (4), t 1u (4)-and h g (1), a g (2)-modes that are active in absorption. Bands involving the h u (4)-and t 1u (4)-modes in the emission process have also been identified in the fluorescence spectrum. The appearance of the 0 0 0 -band in the forbidden 1 1 T 1g ← 1 1 A g transition is explained by symmetry reduction in the C 60 +environment system due to the interaction of electrons with local phonons. The temperature coefficients of the red shift for the 256.3-and 328.3-nm bands of allowed 1 T 1u ← 1 1 A g transitions for C 60 in hexane are equal to -1.45 and -0.46 cm -1 ⋅K -1 , respectively. The peak and half-width values of the 337.2-nm band for C 60 in polystyrene remain unchanged on cooling to 77 K. Absorption in the 700-800-nm region for concentrated hexane solutions of fullerene at 292 K results from the production of (C 60 ) n -clusters.Keywords: vibronic spectra, broadening, temperature effect, dispersion interactions, 0-0 band, solvatochromic shift, (C60)n-clusters.Introduction. The spectral properties of fullerene C 60 are interesting because of the broad application of materials based on carbon nanoparticles in science, industry, and medicine [1][2][3][4][5][6][7]. The solution of several astrophysical problems was also directly related to the study of the spectral properties of fullerenes [8,9]. Polymers that can be used as a basis for creating optical emission limiters, photo-conducting materials, and materials suitable for transforming solar energy into electrical are being sought [3, 10-12]. For example, the ability of C 60 bound covalently to phthalocyanine to transform long-lived (0.2 ms) photoinduced states with charge separation [11] was used to fabricate a solar cell in which the polymer matrix acted as an external light-collecting antenna and effected charge transfer into the reaction center, the phthalocyanine-fullerene dyad [12].Fullerene C 60 is a spherical molecule with point-group symmetry I h . The unique structure is responsible for its unusual photophysical properties that differ substantially from those of heterocyclic compounds. The vibronic spectra of C 60 exhibit both allowed and symmetry-forbidden transitions. Extensive theoretical and experimental investigations enabled bands and lines in spectra of fullerene C 60 to be identified [9,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] and general trends of the shift upon changing the nature of the medium to be explained [13,14]. As a rule, n-alkanes were used as the solvents [13,14]. The bands and symmetry assignment of transitions for C 60 have been described in detail [16]. Measurements at low temperatures were made in glassy solvents such as toluene [15], 3-methylpentane, and hexane [16,17] at 77 K, in inert-gas matrices at 4.2 K and lower [9,18,19,26], and in the gas phase (in molecular beams cooled by expansion) [21][22][23][24]....

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The effect of dispersion interactions on the electronic spectra of organic compounds is analyzed within second-order perturbation theory. A formula is obtained which makes is possible to determine the change in the polarizability of the molecules upon excitation, ∆α eg , using data on the effect of the bulk polarizability P n of the solvent on the position of the electronic spectrum. It is shown that when the solutions are cooled, the long-wavelength shift of the absorption spectra for the studied anthracenes in alcohols is mainly due to dispersion interactions and is caused by an increase in P n . The possibility of using the new formula for ∆α eg is demonstrated for anthracenes as an example. It is found that for anthracene, 1-chloroanthracene, 9,10-dichloroanthracene, 9,10-dibromoanthracene, 9,10-diiodoanthracene ∆α eg is 16.5, 16.9, 17.2, 18.6, and 20.2 Å 3 respectively.