Preparation and characterization of alternating copolymers containing fluorene and thiophene derivatives

A series of fluorene-based polymers with alkylsulfanyl, alkylsulfinyl and alkylsulfonyl substituted thiophene were synthesized by the palladium-catalyzed Suzuki coupling reaction and the structures were confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry. The results of the absorption and emission spectra reveal that the substituents on the thiophene ring strongly affect the planarity of the polymer chains. The interruption of the effective conjugation length through the non-planar conformation results in high photoluminescence quantum yield. Cyclic voltammetry analysis of the polymers was observed that the non-planar polymers increased the band gap and decreased the highest occupied molecular orbital level. Differential scanning calorimetry trace confirmed that the less steric hindrance of substituents on the thiophene ring would increase the intermolecular interaction and the crystallinity of the polymers.