A general formula for the difference of solvent shifts of fluorescence and absorption spectra in the approximation of long range dipolar interaction was derived using Ooshika’s theory of light absorption in solution. Measurements of fluorescence and absorption spectra of some naphthalene derivatives in various organic solvents were undertaken, and the data were analysed by the theoretical formula. The formula reproduces the experimental data satisfactorily, and from this fact it was concluded that the most predominant factor which determines the difference of solvent shifts of fluorescence and absorption spectra of these molecules is the interaction energy between solute and solvent molecules due to orientation polarization. The incremental values of dipolemoments in the excited state were estimated, and those for α-, β-naphthols and β-naphthyl methyl ether were interpreted as due to the increase of electron migration from the substituent in the excited state.

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To elucidate the dynamics and mechanisms of radiationless transitions from higher excited electronic states as well as the ultrafast intramolecular vibronic relaxation in porphyrin derivatives, we have studied the fluorescence dynamics of Zn-tetraphenylporphyrin (ZnTPP) and Zn-diphenylporphyrin derivatives (ZnDPP) in fs-ps time regimes by means of fluorescence up-conversion technique. Detailed measurements on ZnTPP in ethanol have demonstrated fluorescence dynamics over the whole spectral range from 430 to 620 nm when excited to the S 2 state. The time constant (∼2.3 ps) of the single-exponential decay of S 2 fluorescence around 430 nm agreed with that of the single-exponential rise of S 1 fluorescence around 600 nm (wavelength of 0-0 transition in the stationary spectrum), indicating that the relaxation by the ultrafast vibronic redistribution immediately after S 2 f S 1 internal conversion mainly gives lower vibronic states near the bottom of the S 1 state. However, we have observed the dynamics of weak hot fluorescence probably from the nonrelaxed vibronic state immediately after internal conversion and also higher vibronic states in S 1 formed in competition with the main product of the vibronic redistribution, all over the wavelength region between S 2 and S 1 . Preliminary results of our studies on ZnDPP were very similar to those of ZnTPP.

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