Photoinduced Carrier Generation and Distribution in Solution-Deposited Titanyl Phthalocyanine Monolayers

We prepared titanyl phthalocyanine (TiOPc) monolayers on sapphire prism supported Au{111} substrates through solution deposition and characterized their photo-responses using a custom built laser assisted scanning tunneling microscope under ambient conditions. Two types of lattice structures (hexagonal and rectangular) were observed and the distributions of photoinduced charges were measured under evanescently introduced 633 nm and 780 nm laser illumination. The distributions of photo-excited electrons in molecules in hexagonal lattices match theoretically calculated charge density changes in TiOPc molecules upon excitation. However, the photo-responses of TiOPc molecules in rectangular lattices are different than those predicted and TiOPc molecules in these arrangements may have lower excitation probabilities at 633 nm and 780 nm. Our results suggest that the photo carrier generation efficiency of TiOPc molecules is related to their packing arrangements in monolayers and local environments. The growth me...