Molecularly Modified Organic Semiconducting Properties of Phthalocyanine Derivatives
Hisao YANAGI, Masanobu KAWAGISHI, Derck SCHLETTWEIN and Dieter WOHRLE
Abstract:Phthalocyanie, one of the most common organic semiconductor molecules, was molecularly modified and its electronic structure was investigated by means of visible spectroscopy, photoelectron emission analysis and molecular orbital calculations. The exchange of ƒÎ-conjugating carbon and nitrogen atoms in the four-fold macrocyclic ring of zinc phthalocyanine (ZnPc) yielded tetrapyrido-tetraazaporphyrinatozinc (ZnTAP(Py)4) and tetrabenzporphyrinatozinc (ZnTBP). The replacement of the four aza nitrogen atoms in the meso position of ZnPc with the methine groups resulted in a pronounced Soret band in the absorption spectrum of ZnTBP due to the change in its frontier orbital distribution. The ionization potential increased in the order of ZnTBP < ZnPc < ZnTAP(Py)4, accordingly to the caluculeated electronic energy levels of the highest occupied molecular orbitals. Electronic delocalization at the pyridine groups in ZnTAP(Py)4 lowered the molecular orbital energies, which also leaded to the observed n-type behavior as compared to the p-type conduction of phthalocyanines. Key Words:Phthalocyanines, Organic semiconductor, Molecular modification, Photoelectric effect, Molecular orbital calculation