PICOSECOND DYNAMICS OF AN IR SENSITIVE SQUARAINE DYE - ROLE OF SINGLET AND TRIPLET EXCITED-STATES IN THE PHOTOSENSITIZATION OF TIO2 NANOCLUSTERS

The photosensitization properties of a novel squaraine dye is probed u sing picosecond laser flash photolysis, The dye which exists in a prot onation equilibrium with a pK(a) of 4.9 has a strong absorption in the IR region. The protonated form of the dye is highly fluorescent and i s readily quenched in colloidal TiO2 suspensions. The association cons tant as determined from the quenching studies is 1.25x10(3) M(-1). The singlet excited state of the protonated form of the dye participates in the charge injection process with a heterogeneous electron transfer rate constant of 8.3x10(9) s(-1) The unprotonated form of the dye inj ects electrons from both the singlet and triplet excited state with el ectron transfer rate constants of 1x10(10) s(-1) and 1.25x10(9) s(-1), respectively. (C) 1997 American Institute of Physics.