Experimental study of end-capped acceptors influencing the photo-physical, electrochemical and thermal parameters of A-D-pi-D-A type small molecular electron donors

摘要

We have designed A-D-pi-D-A type three new small molecular donor materials denoted as FD-IND, FD-DCV and FD-NBR, which have been synthesised and their photo-physical, electrochemical and thermal properties explored. The synthesised materials have fluorene as "pi-spacer," dithieonopyrrole as "Donor" (D) and various "Acceptor" (A) units are 1,3-indanedione (ND), dicyanovinylene (DCV) and N-butyl rhodanine (NBR). All these three materials have good solubility (similar to 30 mg/mL) in most common organic solvents and have relatively broad absorption in the visible region covering the range of 300-650 nm with two primary absorption bands. The absorption bands located at shorter wavelength region are ascribed to a localized aromatic pi-pi* transition of the A-D-pi-D-A system, while the bands at longer wavelength are mainly attributed to an ICT transition. All the compounds exhibit excellent thermal stabilities in the range of 260-373 degrees C. Cyclic voltammetry data provided HOMO values as -5.26, -5.32 and -5.32 eV for FD-NBR, FD-DCV and FD-IND respectively. LUMO values estimated from HOMO values and optical band gap are -3.27, -3.22 and -3.37 eV for FD-NBR, FD-DCV and FD-IND respectively. Therefore, these are potential molecules for organic solar cells.