Monomer and dimer emissions in the solutions of a monosubstituted polyacetylene

Photoluminescence (PL) of tetrahydrofuran solutions of a monosubstituted polyacetylene with liquid crystalline pendants, poly(11-{[4′-heptoxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (1), has been investigated. Intense ultraviolet emission (∼370 nm) has been detected in its dilute solution (2.5 μM). As the solution becomes concentrated (up to 39 mM), the emission color changes to deep blue and finally to blue (∼430 nm). In addition to the large-scale red shift in PL peak, its luminescent intensity changes about two orders of magnitude. Based on the extended Hückel tight-binding calculations, the 370 nm peak is assigned to monomer emission, which originates from the biphenyl mesogen in the pendants, and the peak at 430 nm corresponds to dimer emission, which is related to the aggregates formed in concentrated solutions. Lyotropic mesophase was observed as 1 dissolves in tetrahydrofuran.