Poly(naphthylenethiophene)s and poly(naphthylenevinylenephenylenevinylene)s: effect of naphthalene positional isomers on the light emitting properties of their polymers

Poly(naphthylenethiophene)s and poly(naphthylenevinylene-phenylenevinylene)s prepared from 1,5-dibromo-3,7-di-t-butylnaphthalene showed a significant blue shift in their UV–vis and photoluminescence spectra compared to copolymers derived from the 1,4-naphthylene system, both in solution and in thin film. This is correlated to a change in conjugation effect of the two positional isomers of naphthalene in the polymer backbone, where in 1,4-conjugation an aromatic sextet remains intact in one of the naphthalene rings whereas 1,5-conjugation involves the loss of resonance energy in the entire naphthalene unit. The series of poly(naphthylenevinylene-phenylvinylene)s emitted blue-green light with very high fluorescence quantum yields (80–95%) in solution. A fabricated device showed external quantum efficiency estimated at 0.2–0.4%, with a relatively high turn-on voltage at ∼7.0 V.