Solvation Dynamics of the Excited 1,2-(p-Cyano-p‘-Methoxydiphenyl)-Ethyne†

Solvation dynamics of 1,2-(p-cyano-p‘-methoxydiphenyl)-ethyne (CMPE) in various solvents were investigated by observing its time-resolved fluorescence and transient absorption in the picosecond regime. Anisotropy decays of CMPE in most of the solvents examined were apparently single-exponential, except for n-butanol, in which the decay was nonexponential. Dipole moment of CMPE in the excited state (μe), limiting anisotropy (A0) and rotational diffusion coefficient (D0) were obtained from the anisotropy decays with the theoretical expression based on continuum model combined with a nonlinear least-squares's method. The values of μe were linearly dependent on the solvent polarity except for benzene (9.9 D), and were 3.4 D in diethyl ether, 5.7 D in tetrahydrofuran, 13 D in n-butanol, 17 D in acetonitrile and 42 D in dimethyl sulfoxide. From transient absorption spectral measurements, it was demonstrated that the CT states appeared with time less than 10 ps in acetonitrile, 10 ps in methanol and 20 ps in dio...