Novel fluorene-based conjugated copolymers with donor-acceptor structures for photovoltaic applications

A series of novel copolymers with fluorene and 2-pyran-4-ylidene-malononitrile (PM) moieties were synthesized successfully through Suzuki coupling reactions. The structures and properties of these polymers were characterized using FT-IR, NMR, UV-vis, elemental analysis and cyclic voltametry. All of the copolymers exhibit excellent solubility in common organic solvents. The electrochemical and photophysical properties were investigated, and the results show that the spectral response of these copolymers are extended up to 560 nm, 640 nm, 625 nm and 625 nm for P1, P2, P3 and P4, respectively. The PL spectra of the copolymer and TiO2 bulk-heterojunction films exhibit strong photoinduced electronic interactions. Cyclic voltanmetry studies reveal that the band gaps of these copolymers range from 1.7 to 2.0 eV, implying that they may be promising candidates for solar cells.