Theoretical Investigation of the Structural and Spectroscopic Properties of Anthracene Dimers

Knowledge of the structural and spectroscopic properties of luminophore films is of great scientific and practical interest for the development of optical systems of information recording and displaying in microand nanooptoelectronics, solution of problems of solar energy converters, design of sensors, etc. [1, 2]. Organic dye molecules are densely packed in thin solid films; therefore, their optical properties are complicated by intermolecular interactions. All photoprocesses in this case proceed in supramolecular systems comprising molecular and aggregated dye species. Unlike monomer molecules, the photoprocesses in aggregates have been studied insufficiently. On the other hand, these investigations are very urgent and promising for synthesis of nanocomposite materials with preset photophysical properties. Limited ranges of luminophore molecule orientations in thin films allow the researchers to form molecular complexes with the known geometry using molecules with definite chemical composition and hence to predict the physical and chemical properties of these systems. For this reason, in the first stages of studying the photophysical and spectroscopic processes in luminophore complexes it becomes urgent to investigate their possible geometrical orientation. The inverse problem of retrieval of the luminophore geometry from the spectroscopic characteristics is also urgent. Nowadays the geometrical characteristics of large molecules and of their complexes are investigated both experimentally and theoretically. X-ray structural analysis and magnetic nuclear resonance spectroscopy are sufficiently reliable experimental methods of investigation of spatial arrangement of atoms in molecules [3]. The methods of quantum chemistry provide the basis for theoretical investigations of the geometrical structure of molecules. Results of recent calculations demonstrate that such methods of quantum chemistry as the density functional theory (DFT) and ab initio calculation methods allow the geometrical structure of molecules and of their complexes to be calculated with sufficiently high accuracy often not worse than the accuracy of measurements by experimental methods [4–6]. The anthracene dimers as objects of research were chosen due to the fact that in most cases, the anthracene dimers were used as luminophores in thin films [7]. At the same time, investigations of the spectral and geometrical properties of these complexes are poorly reflected in the scientific literature. Works devoted to calculations of the geometry by the methods of symmetry adapted perturbation theory (SAPT) [8] and second-order Moller–Plesset theory (MP2) [9] are few in number. However, in these works the small 6–31G Pople basis set was used. The geometrical