A charge-separated pair in thin crystals of oxotitanium(IV) phthalocyanine revealed by means of femtosecond time-resolved absorption

The formation and decay of a charge-separated pair in novel polymorphs of thin crystalline oxotitanium(IV) phthalocyanine (OTiPc)n (n>2) were studied by means of femto-second time resolved absorption spectroscopy. A rapid change of the time-resolved absorption spectrum in the range of 420–620 nm revealed that one-third of the intrinsic exciton of β-OTiPc &z.dfnc; exhibiting an absorption maximum around 550 nm was converted within 1 ps to a charge-separated pair exhibiting the absorption bands at 430, 510 and ca. 860 nm, which were assigned to a charge-separated pair. The assignment of cationic is π radical <f>(OTiPc)n−1+</f> (n≥3) is based on the dimer formation of cationic radical in a solution of metallo-phthalocyanine. The anionic radical exhibits a similar absorption spectrum to that in a diluted solution. A time-resolved absorption spectrum of an amorphous crystal was also studied. [Copyright &y& Elsevier]