Analysis and interpretation of experimental UV-Vis absorption spectra of benzochalcogenadiazoles and quinoxaline heterocycles through TDDFT.

CONTEXT

Luminescent liquid crystals, particularly those derived from heterocyclic quinoxalines and benzochalcogenadiazoles, have garnered interest for their combined photophysical and mesomorphic properties. These compounds feature central heterocycles (selenium, oxygen, sulfur, or quinoxaline) connected to phenyl groups via triple bonds, with terminal alkoxy chains of uniform length. Their photophysical properties arise from conjugated systems involving delocalized electrons, while mesomorphic behavior depends on chain size and functional groups. This study performed a comparative analysis of experimental UV-vis absorption spectra against TDDFT computational calculations to clarify the photophysical properties of quinoxaline, 2,1,3-benzoxadiazole, 2,1,3-benzothiadiazole, and 2,1,3-benzoselenadiazole derivatives. Insights into the effects of scalar relativistic corrections and long-range functional adjustments on absorption energies are provided.

METHOD

Time-dependent density functional theory with the polarizable continuum model, available in the Gaussian 09 program, was used to simulate UV-Vis absorption spectra. Calculations utilized the CAM-B3LYP, B3LYP, and M062X functionals, along with basis sets incorporating scalar relativistic corrections via the Douglas-Kroll-Hess transformation. The impact of various functionals and the size of the basis set on the excitation energies was evaluated, especially for selenium-containing compound. The emission spectra in toluene were calculated with the ORCA 5.0.3 code. Experimental UV-Vis absorption and emission spectra were recorded in toluene for comparison with theoretical predictions to determine the most accurate computational approach.