Effects of porphyrin structure on the complex formation behavior with clay

The complex formation behavior of three cationic porphyrins with clay was examined. The porphyrins, which have four cationic sites (TMPyP4+), eight cationic sites (TAEPyP(8+)), and two cationic sites and two anionic sites (DPy2+DS2-P), were used. For all porphyrin, aggregation was not observed in the clay complexes even at the saturated adsorption conditions. The average intermolecular distances in the complexes are calculated to be 2.4, 2.8 and 2.1 nm, respectively. It turned out that intermolecular distances between porphyrin molecules in the complexes could be controlled by modifying porphyrin structure. In the cases of TMPyP4+ and TAEPyP(8+), there was no fluorescence quenching behavior, while DPy2+DS2-P exhibited moderate fluorescence quenching in fluorescence measurement. The difference of intermolecular distance is supposed to affect its behavior in the excited singlet state. It should be noted that no fluorescence quenching behavior even in such high density adsorption conditions on inorganic surface is very rare and unique. The complexes are, thus, promising to construct one of the proto-type of efficient light-harvesting system without unexpected fluorescence quenching. (C) 2009 Elsevier Inc. All rights reserved.