Ring-expanded porphyrins as an approach towards highly conductive molecular semiconductors

As an approach to obtaining molecular semiconductors with high conductivity, it was attempted to lower the activation energy of conduction by enlarging the π-conjugated system in porphyrin materials. An anthraporphyrin (ZnTAnP) has been synthesized for the first time, and the spectroscopic, electrochemical and semiconductive properties have been characterized as a function of increasing molecular size, in the order: tetraphenylporphyrin (ZnTPP), tetrabenzoporphyrin (ZnTBP), tetranaphthaloporphyrin (ZnTNP), and ZnTAnP. With enlargement of the macrocycle, the Q band shifts to the red, and the absolute values of oxidation and reduction potentials become smaller. Room temperature conductivities of air-doped ZnTPP, ZnTBP, ZnTNP, and ZnTAnP thin films are < 10^-11, 4 × 10^-10, 3 × 10^-4 and 1 × 10^-7 Ω^-1 cm^-1, respectively. The smaller conductivity of ZnTAnP appears due to the formation of a stable charge transfer complex with oxygen.