New peripherally-substituted naphthalocyanines: synthesis, characterisation and evaluation in dye-sensitised photoelectrochemical solar cells

A series of novel tetra-substituted naphthalocyanines featuring hydroxy and carboxylate substituents in peripheral positions have been synthesised in reasonable yields and characterised by spectroscopic techniques. The photochemical properties of the tetra-acid derivative 7 were examined following immobilisation on a nanocrystalline TiO2 surface and photoinduced dye cations were observed following optical excitation. 7 has a redox potential of 0.25 V (vs. Ag/AgCl), which is lower than is required for an efficient regeneration reaction and, therefore, results in limited photocurrent flow when 7 is used in photoelectrochemical solar cells.