Synthesis and energy gap studies of a series of sulfone-substituted polyphenylenevinylenes (SF-PPVs)

A new polyphenylenevinylene (PPV) with alkoxy and sulfone substitutions on every phenylene unit has been synthesized and characterized. This polymer completes a series of sulfone (SF) containing PPVs (SF-PPVs) that are characterized by an increasing content of sulfone-substituted phenylene and allow one to observe the effect of electron withdrawing as well as intra-ring donor–acceptor strong coupling between RO and sulfone, both affect the frontier orbital energy levels and energy gaps of the polymer. The SF-PPVs show a consistent increase in energy gap with increase in the content of the RO- and sulfone-substituted phenylene unit, a phenomenon rarely observed among synthesized conjugated polymers in the literature. Calculation of model compounds (dimers) confirmed that the charge-transfer interactions between RO and sulfone leads to certain degree of intra-ring transformation from benzoid to quinoid form, which reduces electron delocalization along the π-conjugation in backbone and causes an increase in the polymer energy gap.