Strong photoluminescence from monosubstituted polyacetylenes containing biphenylyl chromophores

Monosubstituted polyacetylenes are generally regarded as unlikely candidates for photoluminescent materials. We have, however, observed intense deep-blue emission in a series of photoexcited poly(1–alkynes) (PAs) containing biphenylyl pendants (–{HC=C[(CH2)m–OCO–biphenyl–OC7H15]}n–where m=2, 3, 4, and 9). The photoluminescence (PL) is readily observable by naked eyes under normal room illumination conditions, whose integrated intensity is threefold 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 the PAs. Using the extended-Hückel-tight-binding method, we have calculated the density of states of the PAs, and it is found that the functional pendants have dramatically modified the band states of polyacetylene. The strong PL of the PAs is satisfactorily explained by the engineered electronic structures.