The maximum absorption wavelength (lambda(max)(abs)), emission wavelength (lambda(em)) and the related oscillator strength (f) of the maleimides in the ground and first excited states were calculated by using the DFT, CIS and the time-dependent density functional theory (TD-DFT) methods, where the molecular structures were optimized by DFT/B3LYP/6-31G* calculation. Solvent effects on the maleimides were examined using the PCM simulation at DFT/B3LYP level with the 6-31G* basis set. For N-substituted maleimide, the substituent gives only a slight influence on the maleimide chromophore, while planar conformation of PhMLH leads to the improvement in pi-delocalization from substituent to maleimide unit. For 3,4-substituted maleimide, the steric repulsion between substituent and maleimide chromophore influences the extent of pi-delocalization and the molecular conformation. The calculated (lambda(max)(abs)) and lambda(em) of maleimides are in good agreement with the experimental data. In the gas phase, both absorption and emission peaks are red-shift as compared to the non-substituted maleimide. Under solvent environment, the more planar conformation of PhMLH shows a blue-shift in the calculated (lambda(max)(abs)) and lambda(em) as compared with other N-substituted maleimides. For 3,4-substituted maleimides, the effect of substitution produces the most significant spectral red-shift as compared to other maleimides. (C) 2008 Elsevier B.V. All rights reserved.
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JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM Volume: 860 Issue: 1-3 Pages: 58-63
