Picosecond Time-Resolved Resonance Raman Spectroscopy and Vibrational Analysis in Spirooxazine Photochromism

Spectral properties of spirooxazine photochromes: TD-DFT insights

A large series of photochromes of the spirooxazine family has been investigated using density functional theory and time-dependent density functional theory, aiming at designing molecules with an open-ring merocyanine form absorbing at the longest possible wavelength. A complete methodological assessment (basis set, solvent effects, functionals) has been performed, allowing the design of efficient multilinear regressions for two solvents (cyclohexane and toluene). These regressions allow the estimate of the absorption wavelength of open spirooxazine with an error limited to about 5 nm. The thermodynamic and spectral properties of several isomers have been considered, and it turned out that only TTC and CTC structures may appear experimentally. These structures present similar stabilities and absorption wavelengths. The impact of the auxochromic groups on the UV/vis spectra was assessed and novel promising substitution patterns have been unravelled. It is shown that using a strong push moiety on the same side of the molecule as the pull group may be an effective procedure for tuning the visible spectra. In particular, several spirooxazines with absorption wavelength predicted to be close to or larger than 700 nm are proposed.

Quantum Chemical Study of the Photocoloration Reaction in the Napthoxazine Series

Ab initio and semiempirical quantum mechanical calculations were performed to study the electronic spectra of spiroxazine photochromic compounds as well as the corresponding photoisomers. Ground-state geometries were optimized based on density functional theory (DFT). Excitation energies of the different forms were calculated using the time-dependent density functional theory (TD-DFT) method. Semiempirical calculations including configuration interactions were performed to detail the mechanism of ring opening in excited states. On the basis of the obtained potential energy profile, a complete mechanism of photocoloration able to clarify some experimental findings is provided. A correlation of the experimental quantum yield of photocoloration with the calculated properties as a function of substituent effects is proposed.

7-Trifluoromethylquinoline-Functionalized Luminescent Photochromic Spiropyran with the Stable Merocyanine Species Both in Solution and in the Solid State

A new spiropyran (SP2) with the stable merocyanine form (MC2) both in solution and in the solid state at room temperature was designed and synthesized. The stability of MC2 is believed to be due to the electron-withdrawing effect of both the quinoline and the trifluoromethyl groups. (1)H NMR spectra indicate that the ratio of the open form vs the closed form of SP2 is dependent on the polarity of solvents. Single crystals composed of only the open form (MC2) were successfully obtained. X-ray structural analysis indicates that except trifluoromethyl and two methyl groups MC2 is completely planar with an s-trans,s-cis conformation. It should be noted that this is the first report of the X-ray crystal structure of the pure open form of spiropyran. MC2 can be slowly transformed into SP2 at -30 degrees C or lower temperature, and the process is accelerated by visible light irradiation. This special photochromic behavior can be explained by the calculated thermodynamic data. The spectral properties of SP2/MC2 in the presence of different metal ions are also studied, and the results show the potential application of SP2/MC2 in sensing metal ions.