Picosecond Laser Photolysis Studies upon Photochemical Isomerization and Protolytic Reaction of a Stilbazolium Betaine

The phofoinduccd rransjcis isornerization is one of the 111051 important fundamental processes in photoclwlttical and photobiological reactions. and many invcsrigarions have been carried out in order to elucidate its mechanism. Recently. direct observation of rhe isomcrization process in rhe singlet excited state 113s become possible owing to the development of p~i~~~md iascr spectroscopy. Up 10 now. however, Ihe syswtiis studied with this method are rather limircd. The pisosccond studies have been concentrated (VI s:ilbcncs [ 11 and rhodopsins [I!]_ -4 picosecond ISWI phorolysis study of the singlet exited state of thioindigo has also been reported recently [3_3]. On the 011Icr hand. a detailed study of the photokwwrizaiion 1x1s been made in the merocyanine dye 411‘ stilbszolium betriine (U) rype by nuking the meastuements ul‘rhe reaction yields with the stationary ~~t~-rhod l-5]_ Acsoriiing lo this study. hltr,lns is more ?;1;11>k llI3Il hl,is rtnd does not show photoisomerizaI~~UI. 1 lo\vcvcr. the 0-protonared form (hlH+) readily