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The resonance and pre-resonance Raman scattering in the low energy 11B2u and 11B3u states of 1,4,5,8-naphthalenetetracarboxy dianhydride in terms of DFT methods. The aggregation of NTCDA molecules in the ethanol and methanol solutions



The absorption, pre-resonance, and resonance Raman spectra of 1,4,5,8-naphthalenetetracarboxy dianhydride (NTCDA) molecule are examined in terms of time-dependent density functional theory at TD-B3LYP/aug-cc-pVDZ and TD-SVWN/aug-cc-pVDZ levels. The Franck–Condon analysis performed for two 11Ag → 11B2u and 11Ag → 11B3u overlapping transitions leads to an excellent agreement between the theoretical predictions and experimental data providing that the calculated absorption is confronted with that measured in chloroform or acetonitrile but not in the ethanol (methanol) solution. We argue that absorption spectra measured in ethanol solution already known in literature do not characterize NTCDA molecule. On the basis of the absorption and resonance scattering spectra, we may deliberate that the dimerization of NTCDA is responsible for utterly different absorption observed in ethanol (methanol) comparing with less active solvents (chloroform and acetonitrile). That conclusion is supported by the dimer vibronic theory and by the TD-B97d computations at the aug-cc-pVDZ basis set level. Copyright © 2013 John Wiley & Sons, Ltd.