Abstract: The influence of surface-adsorbed NO_2 on the surface photovoltaic properties of MnPc and the related charge transfer interaction were studied by surface photovoltage spectroscopy. In comparison with other metal-phthalocyanines, the photovoltaic response of MnPc is very particular. A strong photovoltaic response band near 510 nm was observed besides B band (365 nm) and Q bands (640, 725 nm), which was assigned as the MLCT transition from the e_g(d_(xz), d_(yz)) orbital of central manganese ion to the b_(lu)(π~*) orbital of Pc ring. Under given conditions, the MnPc exhibited reverse photovoltaic response after adsorbing NO_2 and, consequently, the spectral distribution changed remarkably, which suggests that there is a strong charge transfer interaction between them. The photodesorption experiments indicated that NO_2 was adsorbed by the atomic oxygen bridged dimer of MnPc prior to the MnPc monomer and made the dimer partly decomposed. Besides, there is a selective interaction between NO_2 and MnPc with respect to the various electron transitions of MnPc.

Key words: MnPc, Surface-adsorbed NO₂, Surface photovoltaic properties