Surface photovoltaic properties of an expanded aza H2Pc containing four 1,10-phenanthroline subunits

The photovoltaic properties of an aza H2Pc containing four 1,10-phenanthroline subunits were investigated by means of surface photovoltage spectroscopy and electric-field-induced surface photovoltage spectroscopy. The surface photovoltaic response was enhanced under positive electric field and weakened under negative electric field. Thus, the expanded aza H2Pc was judged to be p-type semiconductor. From the similar response behavior, the Q-band and high-energy side of Soret-band were assigned to π-π* transition. Interestingly, the low-energy side of Soret-band exhibits blue shift under external electric field. According to the influence of electric field on the ground state of n-orbital with high polarizability, it was assigned to n-π* transition. We think the peripheral substituent units play a key role in the electronic transition and photovoltaic processes.