Symmetric and unsymmetric substituted 1,5-diarylthiocarbazones, and their mono- and bismercury complexes, were synthesized for spectral analysis. The first singlet–singlet transition of the mercury complexes was determined and the spectral shift produced by trifluoromethyl substitution was compared with that caused by different substituents in similar complexes. The large magnitude of the hypsochromic shift produced by the trifluoromethyl substituent can be explained by concerted steric and inductive effects, while the smaller bathochromic shift induced by the methoxy substituent is a result of opposing steric and electronic effects. In the trifluoromethyl substitution, a hypsochromic shift caused by steric influences was found to be 500 cm⁻¹ in the photochromic unactivated state, and 250 cm⁻¹ in the photochromic activated state. A similar shift caused by inductive influences was found to be 750 cm⁻¹ in the photochromic unactivated state, and 600 cm⁻¹ in the photochromic activated state. The smaller spectral shift observed in the photochromic activated state is consistent with the elucidated structure of the unsymmetric 1,5-diarylthiocarbazone, 6d, which was shown that the trifluoromethyl substitution was on the phenylazo portion of the molecule by chemical and spectral studies.