Dear CCLers, I have a question regarding the simulation of electronic transitions : I calculated the UV-Vis spectra of two molecules using TD-DFT with a B3LYP/6-31G(d,p) + PCM The results are very good for one of the two moleules and very bad for the other. The two molecules are based on a 1-10-phenanthroline substituted in position 3 & 8 by two bithienyls. The spectrum of this molecule is very well reproduced. If I add 2 methyls in position 2 & 9 of the phenanthroline this induces a twist and breaks a bit the conjugaison. For this second molecule, the experimental spectrum shows a red shift of 70nm but only 20nm according to the calculation. Do you have an idea of the reason of this differance ? is it linked with the geo-optimisation (should I increase the basis set size ?) or with TDDFT ? Another question : is it possible to calculate fluorescence spectra using Gaussian or another QM software ? Thank you for your help, best regards. -- Jérôme KIEFFER : http://www.terre-adelie.org
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