Photoluminescence of donor-acceptor carbazole chromophores

Absorption and emission features of various chromophores both in the solid amorphous state and in solution are presented. These 1-(N-ethyl-carbazolyl) -2-substituted-2-cyanovinyline molecules contain in their structure the ele ctron-donor carbazole nucleus and cyanovinylene bearing different acceptor moil:ties such as either another nitrile function, a methylester, a phenyl, or a para-nitro-phenyl group. It is shown that depending on the strength o f the donor-acceptor internal charge transfer, both the absorption and emis sion spectra are more or less red-shifted. It is found that the methylester derivative displays the best relative photoluminescence efficiency among a ll the samples. From solvatochromic studies we showed that the remarkable l uminescence of the cyanoester derivative can be attributed to a strong dipo le moment in the excited state. Furthermore, cyanoester microcrystallites e xhibited spectral narrowing which was attributed to an amplified spontaneou s emission. (C) 2001 Elsevier Science B.V. All rights reserved.