Preferential formation of mixed dimers in aluminium containing porphyrin–phthalocyanine systems: A photophysical study

The interaction of chloroaluminium phthalocyanine and aluminium porphyrin in solution was studied using UV–visible and fluorescence techniques. The spectra of the porphyrin alone exhibited new bands attributed to aggregates and a value of −12.6 kJ mol−1 for the enthalpy of dimerization was obtained. A small dimerization constant of 5.8 × 103 M−1 was found for phthalocyanine homodimers and preferential formation of mixed dimers over porphyrin homodimers was observed experimentally and supported by molecular modelling. kd and ΔH values of 5.7 × 104 M−1 and −21.1 kJ mol−1 were found in the mixed system, along with an enhancement in phthalocyanine fluorescence.