Fluorescent phthalocyanine dimers--a steady state and flash photolysis study.

Steady state and time resolved studies of a tetrakis[(+/-)-2,2-dimethyl-1,3-dioxan-4-ylmethanol] (solketal) substituted zinc phthalocyanine (1) and its derivatives (4a-c) are reported. These compounds form novel fluorescent dimers (or higher order aggregates) at low temperature, with a red shifted emission band centred at approximately 750 nm. The degree of aggregation has been related to the nature of the peripheral substituents, with bulky groups reducing and long alkyl chains increasing the phenomenon. Fluorescence lifetimes of the dimeric species are reported. Flash photolysis results show complex behaviour of the transient species, and it is possible to identify three main processes, involving decay of the monomer triplet state, the dimer triplet, and dimer disaggregation, with each process having a characteristic transient lifetime.