Naphthodifuranone-Based Monomers and Polymers

Abstract

The synthesis of new π-conjugated monomers and polymers containing 3,8-bisphenylnaphtho[2,1-b:3,4-b′]difuran-2,9-dione (1,10-NDF) units in the main chain is described. 1,10-NDF-monomer M1 (3,8-bis(4-bromophenyl)naphtho[2,1-b:3,4-b′]difuran-2,9-dione) was obtained upon condensation of 2,3-dihydroxy-naphthalene and 4-bromo-mandelic acid followed by oxidation with nitrobenzene. M2 (3,8-bis(4-(5-bromo-4-octylthiophen-2-yl)phenyl)naphtho[2,1-b:3,4-b′]difuran-2,9-dione) was obtained upon Stille coupling of 4-n-octylthiophen-2-yl-trimethylstannane and M1 followed by bromination of the thiophene groups with NBS. The X-ray structure analysis of M1 indicated a dihedral angle of 42–45° between the lactam phenyl groups and the NDF core, and weak intermolecular π–π stacking with a distance of 3.36 Å between the chromophors. A HOMO–LUMO calculation of M1 indicates an electron transfer from the phenyl groups to the NDF core upon excitation. Polymers were obtained upon palladium-catalyzed Suzuki and Stille coupling reactions of M1 and M2 with 2,2-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 2,5-bis(tributylstannyl)thiophene. The polymers exhibit broad absorption bands with maxima between 508 and 564 nm and tails reaching up to 1057 nm in thin films, and high extinction coefficients of 1.1 × 104 to 3.9 × 104 L mol–1 cm–1. Band gaps are between 1.45 to 1.63 eV. Photoirradiation studies indicate that the polymers are extremely stable to UV and visible light.