[en] Highlights: • ONIOM procedure with PM3 method was used for terrylene in naphthalene crystal. • Terrylene dye in naphthalene crystal lowers its symmetry from D_2h to C_i. • Lower symmetry of terrylene is reflected by appearance of a new 10b_1g vibration. The ONIOM(B3LYP/6-31G(d,p):PM3) procedure was used for optimization of terrylene molecule embedded into a naphthalene crystal, which crystallographic lattice was described by the PM3 method. Experimentally observed appearance of the new (absent for isolated molecule) vibronic line in fluorescence excitation spectrum of terrylene in the crystal was attributed to lowering of the molecule symmetry from D_2h to C_i. Further refinement of the molecule coordinates was proposed in order to achieve the experimentally observed intensity distribution in the fluorescence excitation spectrum.