In contrast to the "common knowledge" that monosubstituted polyacetylenes are a group of nonluminescent polymers, efficient deep-blue photoluminescence in a series of poly(l-alkynes) has been detected. The emission of the monosubstituted polyacetylenes is readily observable under the condition of normal room illumination, whose integrated intensity is more than three times higher than that of poly(1-phenyl-1-butyne), a well-known highly luminescent disubstituted polyacetylene. A red PL band has also been detected in each of the polyacetylenes. Using the extended-Hückel-tight-binding method, we have calculated the electronic structures of the highly luminescent monosubstituted polyacetylenes. Our results demonstrate clearly that the deep-blue emissions of the monosubstituted polyacetyle...[ Read more ]

In contrast to the "common knowledge" that monosubstituted polyacetylenes are a group of nonluminescent polymers, efficient deep-blue photoluminescence in a series of poly(l-alkynes) has been detected. The emission of the monosubstituted polyacetylenes is readily observable under the condition of normal room illumination, whose integrated intensity is more than three times higher than that of poly(1-phenyl-1-butyne), a well-known highly luminescent disubstituted polyacetylene. A red PL band has also been detected in each of the polyacetylenes. Using the extended-Hückel-tight-binding method, we have calculated the electronic structures of the highly luminescent monosubstituted polyacetylenes. Our results demonstrate clearly that the deep-blue emissions of the monosubstituted polyacetylenes originate from the biphenyl mesogens in the pendants rather than from the distorted backbone.

The electric field effects on the photoluminescence of a tetrahydrofuran solution of a liquid crystalline polyacetylene have been investigated. Remarkable photoluminescence change in spectral shape has been observed only for medium concentrated solution (1.13x10^-2M) but not for dilute and highly concentrated ones. At and above a threshold electric field of ~3.2x10^-5 V/m, its photoluminescence evolves with electric field and dramatic change both in spectral shape and in intensity has been observed. Furthermore, electrically addressable polarized deep-blue photoluminescence has been realized upon photoexcitation by a polarized UV laser beam. The spectral shape and the emission intensity of the polarized photoluminescence can be modulated by external electric fields. Our results suggest that the molecular alignment induced by electric fields and the intermolecular interactions play a key role in the polarized emission.

We have compared the blue emissions (~450 nm) from non-liquid crystalline polyacetylene derivatives. The electronic structures, absorptions and emissions of a series of non-liquid crystalline polyacetylenes demonstrate that neither the soliton nor the perturbed band gap of the backbone is possible to be the origin of the observed blue emissions from polyacetylene derivatives although the band gap of the conjugated backbone can be widened up to ~2.0 eV by the pendants. Our results show the blue emissions of those non-liquid crystalline polyacetylenes are related to the phenyl chromophores in the pendants. Cautions should be excised due to the simple model used in the calculations, and further investigations are required.