The Investigation of Thermal Conversion of Spiropyran to Merocyanine and its Derivatives

: The thermal conversion of spiropyran derivatives (R-SP, R = H, OH, and CF3) to merocyanine (MC) were investigated theoretically in the ground state. In S0, the most stable isomer is SP. In the SP to MC switching, the Cspiro−O bond of SP is broken and ring-opening occurs. Since the cis-isomer is energetically unstable, it tends to reach a stable form with lower energy level. The rotation around the central torsion dihedral angle in cis-isomer ultimately yields trans-isomer. The trans-isomer is energetically stable and the cis-isomer is an intermediate in the conversion of ring-closed form to trans-isomer.