Evaluating the Effect of Heteroatoms on the Photophysical Properties of Donor-Acceptor Conjugated Polymers Based on 2,6-Di(thiophen-2-yl)benzo[1,2-b:4,5-b′]difuran: Two-Photon Cross Section and Ultrafast Time-Resolved Spectroscopy

We investigate the influence of the heteroatom on the electronic and photophysical properties of four conjugated polymers based on 3,7-didodecyl-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b']difuran (BDF) as the donor and 3,6-di(thiophen-2-yl)-1,4-diketopyrrolo[3,4-c]pyrrole (TDPP) or 3,6-di(2-furanyl)-1,4-diketopyrrolo[3,4-c]pyrrole (FDPP) as the acceptor. The polymers with a furan as the linker showed higher extinction coefficients than their thiophene counterparts. Ultrafast fluorescence decay showed that the exciton relaxation process is affected by the type of linker in these conjugated polymers. Theoretical calculations showed that the polymers with a furan as the linker are more planar than their thiophene analogues. Also, theoretical calculation showed that the polymers with a thiophene as the linker have larger transition dipole moments. The two-photon absorption cross sections (TPACS) of the polymers with a furan as the linker were larger than their thiophene polymer analogues. These results suggest that the polymers with a furan as the linker have higher charge transfer character than their thiophene polymers analogues. The photovoltaics performance for these polymers are correlated with their optical properties. These results suggest that furan-derivatives are good candidates for synthetic exploration for long-range energy transport materials in photovoltaic applications.