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 electron-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 of the donor-acceptor internal charge transfer, both the absorption and emission spectra are more or less red-shifted. It is found that the methylester derivative displays the best relative photoluminescence efficiency among all the samples. From solvatochromic studies we showed that the remarkable luminescence of the cyanoester derivative can be attributed to a strong dipole moment in the excited state. Furthermore, cyanoester microcrystallites exhibited spectral narrowing which was attributed to an amplified spontaneous emission. (C) 2001 Elsevier Science B.V. All rights reserved.