Studies on ultrafast reaction processes in solution and establishment of exciplex picosecond dynamics

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(1) We have elucidated dynamic behaviors of exciplex systems and excited singlet EDA complexes in polar solvents by means of time-resolved emission, transient absorption and photocurrent measurements with picosecond (ps) and nanosecond (ns) laser photolysis methods.(2) We have confirmed that TMPD and related diamines in some polar solvents undergo photoinduced charge separation (CS) due to the electron transfer (ET) from fluorescent state to solvent cluster. Moreover, we have deteced ultrashort-lived ion pair produced by ET from Rydberg state pyrene to biphenyl in nonpolar solvent with ultraviolet ps multiphoton laser photolysis method.(3) We have elucidated the mechanism of the ultrafast nonradiative deactivation from the singlet ET state of porphyrin-quinone photosynthetic model systems and strong EDA complexes in polar solvents and have demonstrated the importance of the two step ET in porphyrin-quinone combined systems. Moreover, the mechanism of ultrafast nonradiative deactivation of <pai> -electronic hydrogen bonded systems have been elucidated.(4) We have established the method of ultraviolet ps multiphoton laser photolysis method for investigating the dynamics of excited and ionized states of molecular aggregates such as pure liquids and polymer films and have applied to alcohols, alkylbenzenes and alkanes.(5) We have elucidated the relation between the photoinduced intramolecular charge transfer and trans-cis isomerization of A-CH=CH-D type of compounds.(6) On the basis of above results of laser photolysis investigations, we have developed a new theory of the energy gap dependence of photoinduced CS and charge recombination reaction of produced radical ion pairs taking into consideration the large difference of the solvent photon frequency between the ionized and neutral state and have shown that the observed results can be interpreted satisfactorily by this theory.