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Photoluminescence of donor-acceptor carbazole-based molecules in amorphous and powder forms

We present absorption and photoluminescence features of four samples of carbazole molecules substituted with various electron-acceptor groups. These molecules named 1-(N-ethylcarbazolyl),2-substituted,2-cyanovinylene contain in their structure the electron-donor carbazole nucleus and cyanovinylene bearing either another nitrile function, an ethylester, a phenyl or a para-nitrophenyl groups. 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 ethyl-ester derivative displays the best relative photoluminescence efficiency among all the samples and its peak is measured at 490 nm when taking amorphous thin film. The microcrystalline powder form of the same material exhibits spectral narrowing and shift of the peak emission. We obtain further narrowing of the emission band and further red shifting of the emission when we illuminate transversely a glass capillary containing the crystalline sample by an ultraviolet light-emitting diode (UV LED).

Photoluminescence; carbazole molecules

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