Quantum chemical study of the Cspiro-O bond dissociation in spiropyran molecules

To study the possibility of photochromic transformations in the crystals of bifunctional compounds, quantum chemical B3LYP/6-31G(d) calculations of the C_spiro-O bond dissociation energies were carried out with the Gaussian-03 program for two dissimilar neutral spiropyrans (Sp) and three cations of their salts in the singlet ground state. For C_spiro-O bond dissociation in the cations Sp ⁺ and the neutral systems SpI consisting of Sp ⁺ and I^?, the energy barriers do not exceed 10 kcal mol^?1, increasing when moving from the cations Sp ⁺ to the neutral systems SpI. The changes in the HOMO and LUMO energies when going from the closed to open form of the cations Sp ⁺ correlate with the energy barriers to the corresponding C_spiro-O bond dissociations.