Functionalized Benzothiadiazole Non-Fused A-D-A'-D-A Small Molecules for Effective Electron Mobilities and Metal-free Photocatalysis

Abstract

Three non-fused A-D-A'-D-A π-conjugated metal-free small molecules BT-IT1, BT-IBT2 and BT2F-IBT3 have been synthesized and their absorption characteristics and redox properties, as well as charge carrier mobilities have been investigated. The resultant molecules exhibited broad absorption in the range of 325-600 nm in solutions and in thin films the absorption range is 350-700 nm. These new conjugated small molecules showed low-lying HOMO energy levels (-5.49 to -5.50 eV), deep LUMO energy levels (-3.67 to -3.69 eV) and narrow bandgaps of (E_g ^CV ) ∼0.79 eV. Appreciable electron mobilities for compounds BT-IBT2 and BT2F-IBT3 were 4.56×10^-3 and 1.12×10^-3 cm² V^-1 s^-1 , respectively, obtained by space-charge limited current (SCLC) measurements. Additionally, excellent photocatalytic performances of BT-2T (6), BT2F-2T (10), BT-IT1, BT-IBT2 and BT2F-IBT3 for highly selective oxidation of thioanisole to desired sulfoxides under visible light irradiation were observed.

Keywords: donor-acceptor small molecules; electron mobilities; narrow bandgaps; visible absorption; visible-light photocatalysis.