Comprehensive Theoretical Study of the Conversion Reactions of Spiropyrans:  Substituent and Solvent Effects

Abstract

A comprehensive theoretical study of the reaction mechanisms for the conversion between spiropyrans (SPs) and the open form of merocyanines (MCs) has been conducted by theoretical calculations. The reaction mechanisms on the ground-and triplet-state potential energy surfaces (PESs) were investigated using the density functional method. Time-dependent density functional theory (TD-DFT) calculations using the CIS optimized excited-state geometries were carried out to study the reaction mechanisms on the lowest excited singlet-state PES. Two possible reaction mechanisms for the thermal conversion between SPs to MCs were found on the ground-state PES. The geometrical parameter, BLA (Bond Length Alternation), which correlates the strengths of the substituents and the polarities of solvents, was used to explain the changes in the reaction mechanism induced by the different donor-acceptor pairs and solvents. In addition, the reaction mechanisms of spiropyran/merocyanine conversion on the triplet and the lowest excited singlet potential energy surfaces were also studied; several possible reaction mechanisms on the excited-state PESs were proposed. A comprehensive mechanistic view of the ultrafast photochemistry of spiropyrans was revealed and interpreted in terms of the strengths of substituents and the polarity of solvents.

Dynamics of a photochromic spiropyran under aqueous conditions

“…Our time-resolved measurements reveal that the opening reaction takes place within 1.6 ps via the S1 state, whereas the closing reaction is accomplished within 25 ps after relaxation of the excited state via the merocyanine ground state. This is in accordance with the predictions made by Sheng et al [8]. Its high stability and ultrafast switching in the low picosecond range under aqueous conditions make this compound a versatile tool especially for biological applications [10].…”

Theoretical study on the structure and property relationship of the cationic conjugated polyelectrolytes

“…The TDDFT method has recently been shown to yield relatively accurate excitation energies for large molecules [9,10], and in some cases the TDDFT results are of quality, comparable to those of complete active space with secondorder perturbation theory (CAS-PT2) calculations [11], although at substantially lower computational costs. All the calculations were performed using Gaussian 03 package [12].…”

Construction of Energy Transfer Systems within Nanosized Polymer Micelles and their Fluorescence Modulation Properties

“…The ABC triblock copolymer micelles' absorption behavior in water is similar to that of the methacrylate-linked spiropyran monomer in toluene ( Figure S4) upon UV or visible light irradiation, except that the light scattering effect of micelles makes the absorption curves exhibit a declined trend from low to high wavelength. In addition to the change in absorption behavior upon UV/visible light irradiation, the micelle dispersions also exhibits remarkable variation in fluorescence intensity, as shown in Figure 1 Under the favorable conditions, the spiropyran derivatives can undergo reversible structure interconversion upon alternate UV/visible light irradiation, and the UV or visible light can be applied to reversibly "turn on" and "turn off" the fluorescence of spiropyran moieties; [7][8][9][29][30][31][32] In this study, we also investigated the reversible nature of the fluorescence emission for the ABC triblock copolymer micelles in water upon exposure to alternating cycles of UV and visible light, and the result is illustrated in Figure 2. It can be seen that the fluorescence emission of the micelle dispersion can be reversibly "turned on" and "turned off" by UV and visible light respectively.…”