TD-DFT and LDM studies of the electronic spectrum properties of 2-(2′-pyridyl)benzimidazole derivatives and their related complexes

The absorption spectra of 2-(2′-pyridyl)benzimidazole derivatives and their Be and B complexes were systematically investigated using a localized density matrix (LDM) method and a time-dependent density functional theory (TD-DFT). Comparing the absorption spectra and electronic transition properties obtained by LDM and TD-DFT with the experimental result, the LDM method gives a more reliable approach for determining the electronic spectra of the compounds under study. This method can also substantially reduce computational cost. For 2-(2′-pyridyl)benzimidazole derivatives, the absorption characteristics mostly originate from benzimidazolyl and pyridyl rings with a calculated absorption wavelength of about 300 nm. In addition, the B and Be complexes of 1,4-2-(′2-pyridyl)benzimidazole were studied. The absorption spectra undergo a red shift when B coordination metal ion is substituted by a Be metal ion. The first absorption peak of [Be(II)(4,4′-bis[2-(2′-pyridyl)benzimidazolyl)(benzene)4] clearly appears with the enhancement of oscillatory strength, unlike with [Be(II)(2-(2′-pyridyl)benzimidazolyl)(benzene)2]. The absorption wavelengths of the two Be complexes are both near 430 nm, indicating that their transition properties originate from the ligand-to-ligand charge transfer between phenyl and 2-(2′-pyridyl)benzimidazolyl.