Significance of symmetry in the formation of impurity centers in molecular crystals

On the basis of the assumption concerning the symmetric properties of the free aromatic hydrocarbon molecules and those placed in host crystalline lattice cell, the analysis of the multiplet structure of the optical spectra of impurity centers of some the monosubstituted naphthalenes in naphthalene crystal was performed. The low-temperature fluorescence and absorption spectra of the 2-fluoronaphthalene, 2-chloronaphthalene, and 2-naphthol in crystalline naphthalene have been studied at 4.2 K. The results of the symmetry group theoretical analysis of the spectra multiplet structure are suggested with experimental data. The developed approach was also applied for the analysis of the multiplet structure in optical spectra of rapidly frozen solutions of 3,4-benzpyrene, porphin and its derivative in normal alkanes.