The circular dichroism (CD) and absorption studies of 1,4,5,8-naphthalene tetracarboxydiimide dimer in terms of vibronic coupling theory

Abstract

Abstract The vibronic dimer model is formulated in order to study the absorption and circular dichroism (CD) spectra of (1 R ,2 R )-1,2-bis-( N ′ -cyclohexyl-1 ′ ,4 ′ ,5 ′ ,8 ′ -naphthalenetetracarboxydiimido) cyclohexane (NTD) molecule treated as a dimer with the 1,4,5,8-naphthalenetetracarboxydiimide chromophores. To find out the most stable conformation of the NTD molecule the RHF/STO-3G and the density functional B3LYP/3-21G methods are employed. The results of conformational analysis are shown to be entirely consistent with the experiment. In particular it is shown that the CD and absorption spectra of the NTD dimer observed in the excitation region 25,000–35,000 cm −1 are correctly reproduced by the vibronic dimer model applied with the model parameters directly obtained from CASSCF/5π4n5π * computations. In the debatable region the CD of the NTD dimer results from the 1 1 A g →1 1 B 2 u and 1 1 A g →1 1 B 3 u overlapping transitions in the chromophore. Since that later transition is hidden in the vibronic manifold of the former, the effect of the hidden state on the chiroptical properties of the NTD molecule is discussed in some details.