PICOSECOND LASER PHOTOLYSIS STUDIES ON THE INTRAMOLECULAR PHOTOREDUCTION PROCESS OF BENZOPHENONE BY DIPHENYLAMINE LINKED BY SPACERS IN ACETONITRILE SOLUTION

Photoinduced hydrogen abstraction (HA) processes of 1-(4-benzophenoxy)-3-[4-(phenyl-amino)phenoxy] propane (BP-O-(CH2)3-O-DPA) and 1-(4-benzophenoxy)-2-[4-(phenylamino)phenoxy]ethane (BP-O-(CH2)2-O-DPA) in acetonitrile solution were investigated by means of picosecond transient absorption spectroscopy. The stable ion pair (IP) formation followed by proton transfer (PT) resulting in the HA reaction was observed for the photoreduction of (BP-O-(CH2)2-O-DPA). On the other hand, in addition to inter-ionic PT in the stable IP, direct HA of excited triplet benzophenone ((BP*)-B-3) moiety was observed for BP-O-(CH2)3-O-DPA. On the basis of the dependence of the apparent reaction mechanisms on the molecular conformation and by comparison with the intermolecular HA process, the role of the electron transfer or CT interaction in the HA process of (BP*)-B-3 from the secondary amine was discussed.