Specific effects of water on the relation processes of excited organic molecules

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Effects of solvent water on the relaxation processes of excited organic molecules were studied by means of laser photolysis method, time-resolved thermal lensing method and fluorometry. For aniline and its derivatives, it was found that photoionization is one of the most dominant relaxation channel and that the polarization stabilization of the cation radical produced by photoionization is an important factor to determine the photoionization yield. Excited-state intramolecular proton transfer (ESIPT) reactions of 1-hydroxy-2- acetonaphthone (1H2AN) and related compounds were studied to reveal hydrogen-bonding interations in the excited state of 1-naphthole derivatives. The study showed that 1H2AN undergoes a typical ESIPT reaction, while the excited singlet state of methyl-1-hydroxy-2-naphthoate deactivates without ESIPT reactions. The effects of electronic structures on the ESIPT reaction were clarified for these compounds. Furthermore, it was found that ESIPT of 1H2AN is followed by … More cis-trans isomerization to produce an excited trans-keto form. The , 3-sigmatropic hydrogen shift in the photo-Fries rearranged intermediate of 2,4-dimethoxy-6-(p-tolyloxy)-s- triazine was investigated by using laser photolysis method. Kinetic measurements showed that water and also protic solvents accerelates the rate of the 1,3-sigmatropic hydrogen shift by mutual hydrogen exchange reactions. The electron transfer (ET) reaction from the triplet state of 1,4-dimethoxybenzene (DMB) to the hydronium ion in aqueous solution was studied to reveal effects of the hydronium ion on the photorelaxation processes of organic molecules in aqueous solution. The occurrence of the ET reaction was substantiated by formation of a DMB cation radical coinciding with disappearance of triplet DMB.From kinetic analyses, the rate constant for the ET reaction was determined to be 7.5 x 10^6M^<-1>s-1. The free energy change (DELTAG^0 = +28kJmol^<-1>) calculated for the ET reaction was consistent with the observed rate for the ET reaction from triplet DMB to the hydronium ion. Less