Photoluminescent properties and electronic structures of monosubstituted polyacetylenes: poly{n-[((4′-cyano-4-biphenylyl)oxy)carbonyl]-1-alkynes}

Poly{n-((4′-cyano-4-biphenylyl)oxy)carbonyl]-1-alkynes} (PAnCN, where n=2, 8), which is a class of monosubstituted polyacetylenes with biphenyl mesogens and cyano tails in their pendants, can emit strong deep-blue photoluminescence (PL). In this paper we have investigated their optical absorptions, PL evolutions with excitation power and excitation wavelength, electronic structures, and the electric-field effect on the PL of a moderately concentrated PAnCN solution that had been treated by electric fields. Having been treated by an electric-field pulse (6×10⁵ V/m) for about 3 s, the originally featureless PL spectrum of the PAnCN solution becomes structured and transient, which evolves with time and external electric field. Our results have demonstrated that both the absorption and the deep-blue PL originate from the biphenyl mesogens in the side chains rather than from the distorted backbones.