Push-Pull Fluorophores Based on Imidazole-4,5-dicarbonitrile: A Comparison of Spectral Properties in Solution and Polymer Matrices
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Spectral properties of novel type of fluorophores consist of a π-conjugated system end-capped with an electron-donating N,N-dimethylaminophenyl group and an electron-withdrawing imidazole-4,5-dicarbonitrile moiety were examined. An additional π-linker separating these two structural units comprises simple bond (B1P), phenyl (B2B), styryl (B3S) and ethynylphenyl (B4A) moieties. The absorption and fluorescence spectra were taken in cyclohexane, chloroform, acetonitrile, methanol and in polymer matrices such as polystyrene, poly(methyl methacrylate) and poly(vinylchloride). The longest-wavelength absorption band was observed in the range of 300 to 400 nm. Intense fluorescence with quantum yields of 0.2 to 1.0 was observed in cyclohexane, chloroform and in polymer matrices within the range of 380 to 500 nm. The fluorescence was strongly quenched in neat acetonitrile and methanol. The fluorescence lifetimes are in the range of 1–4 ns for all measured fluorophores. The large Stokes shift (4,000 to 8,000 cm−1) indicates a large difference in the spatial arrangement of the chromophore in the absorbing and the emitting states. The observed fluorescence of all fluorophores in chloroform was quenched by 1-oxo-2,2,6,6-tetramethyl-4-hydroxy piperidine by the diffusion-controlled bimolecular rate (cca 2 × 1010 L mol−1 s−1). Polar solvents such as acetonitrile and methanol quenched the fluorescence as well but probably via a different mechanism.
KeywordsFluorescence Push-pull Imidazol-3,4-dicarbonitrile Polymer matrices
- 18.Birks JB (1968) Photophysics of aromatic molecules, Willey-Interscience a Division of John Wiley and Sons Ltd, New York, London, Toronto, Sidney, Ch 4.: 121–127Google Scholar
- 20.Demas JN, Adamson AW (1971) Evaluation of photoluminescence lifetimes. J Phys Chem 57:2463Google Scholar
- 21.Demas JN (1973) Excited state lifetime measurements. Appendix E, Academic Press, New York, p 245Google Scholar
- 25.Morimoto A, Yatsuhashi T, Shimada T, Biczók L, Tryk DA, Inoue H (2001) Radiationless deactivation of intramolecular charge transfer excited state through hydrogen bonding: effect of molecular structure and hard-soft anionic character in the excited state. J Phys Chem A 105:10488–10496CrossRefGoogle Scholar