The dynamics of solvation of an excited chromophore in pure water and in a restricted space with a limited number of water molecules have been studied. The time-dependent Stokes shift of Coumarin 480 (C480) and Coumarin 460 (C460) were measured using femtosecond fluorescence upconversion and time-correlated singlephoton-counting techniques. The system with a limited number of water molecules was an inclusion complex of Coumarin dyes with y-cyclodextrin (yCD). The results of molecular dynamics simulations are compared with the observed solvent response in pure water and in the yCD cavity. The observed relaxation times range from < fs to 1.2 ns. Solvation of C480 in pure water is observed to occur with time constants of <50 and 310 fs. In sharp contrast with the solvation response in pure water, in the case of the C48O/yCD inclusion complex, additional long solvation time constants of 13, 109 and 1200 ps are observed. The stoichiometry, structure and dynamics of the CoumarinlyCD complexes are also discussed.

Fluorescence decay and polarization of dansyl-labeled poly(methacrylic acid) (PMA) and poly-(acrylic acid) (PAA) have been studied as a function of pH. The decay measurements have shown that, at low pH, PMA chains form highly compact hydrophobic clusters, which are joined by short extended polymer chains. During the transition from the compact to the expanded form, the size of the clusters decreases up to a limit, beyond which the clusters disintegrate completely to an expanded polymer chain. The effect of PMA molar mass and ionic strength on this process was investigated.

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The solvent dependence of absorption and fluorescence spectra, fluorescence lifetimes (τ Fl ), and quantum yields (q Fl ) of various 3-substituted benzanthrone derivatives have been investigated. A consistent correlation between fluorescence quantum yield and emitting state energy has been found that holds for all 6 derivatives in 11 solvents. The experimental data together with the results of semiempirical quantum chemical calculations indicate that the main quenching channel of the fluorescent S 1 (π,π*) excited state is intersystem crossing to an upper (n,π*) triplet state, T N . The rate constant and efficiency of intersystem crossing between these two states are strongly influenced by the substituent and by the solvent polarity, as both modulate the singlet state energy and the S 1 -T N energy gap. The rate constant of direct S 1 f T 1 intersystem crossing is small in most systems but appears to increase with a decrease in the energy of the S 1 state.