Photoelectrochemical Investigations of Molecular Semiconductors: Characterization of the Conduction Type of Various Substituted Porphyrins

The charge transfer from thin film electrodes (thickness ≈ 130 nm) of the zinc(II) complexes of phthalocyanine (1), 2,3,9,10,16,17,23,24‐octacyanophthalocyanine (2), tetrapyrido[2,3‐b; 2′,3′‐g; 2″,3″‐1; 2′″,3′″‐q]‐5,10,15,20‐tetraazaporphyrin (3) and tetrapyrazino[b;g;l;q]‐5,10,15,20.tetraazaporphyrin (4) to oxygen or EDTA dissolved in an aqueous electrolyte was investigated. Illumination with visible light results in photocurrents which are characteristic for each of the studied compounds. The observations are discussed in terms of the band model suitable for molecular organic semiconductors. From the observed predominant direction of the photocurrent a trend in the band positions and the conduction type of the materials 1, 2, 3 and 4 is established. The transformation of a p‐type into a n‐type porphyrin solid can be achieved by appropriate chemical substitution in the ligand system.