Femtosecond spectroscopy of vanadyl phthalocyanines in various molecular arrangements

The relaxation kinetics of excited electronic states of vanadyl phthalocyanines in various molecular arrangements was studied by femtosecond time-resolved spectroscopy. Four types of molecular systems were investigated, i.e., phase I and phase II films prepared on quartz substrates, a thin film deposited on a potassium bromide (KBr) substrate by the organic molecular-beam-epitaxy (MBE) technique, and isolated molecules in a solution and in a host polymer. The excited-state dynamics was found to be strongly dependent on the molecular arrangements in these phases. Dominant relaxation processes were formation of tripdoublet and tripquartet states possessing lifetimes much longer than the lifetimes of hundreds of picoseconds in the isolated molecules, the exciton-exciton annihilation taking place in the picosecond regime in phases I and II with different rate constants, and the subpicosecond exciton decay in the film on KBr.