TD‐DFT study of BIPS spiropyran: Effects of functionals and high‐polarity solvent on C_spiroO bond dissociation and recovery

Abstract

We performed a theoretical analysis of the BIPS photochemical cycle using an extensive set of forty hybrid functionals and taking into account a highly polar solvent (methanol). The functionals with a small fraction of the exact Hartree‐Fock exchange (%HF) showed the predominant S0 → S2 transition with the strengthening of the CspiroO bond. At the same time, functionals with medium and high %HF (including those with long‐range correction) gave a dominant S0 → S1 transition with weakening or breaking of the CspiroO bond, which corresponds to the experimental results. The influence of a highly polar solvent on the photochemical electrocyclic transformations of BIPS turned out to be significant. The number of functionals causing dissociation of the CspiroO bond decreased from 10 to 7 compared to the gas phase. The magnitude of the oscillator strength has increased by approximately one and a half times. Structural distortions of the BIPS molecule during excitation (both with and without CspiroO bond cleavage) significantly decreased in methanol compared to the gas phase. The two strong hydrogen bonds of methanol molecules with the oxygen and nitrogen atoms of spiropyran also have a significant effect on its excitation. They lead to a change in the predominant transition from S0 → S2 to S0 → S1 for five functionals. The number of functionals giving dissociation of the CspiroO bond decreased from seven to four (M08HX, M052X, CAM‐B3LYP, and M11). After the opening of the excited BIPS molecule, both of its strong H‐bonds with methanol are preserved. Of this set of four functionals, only M052X and CAM‐B3LYP exhibited the dominant HOMO‐1 → LUMO configuration observed in high‐level computations by other authors. Therefore, both of these functionals are recommended for modeling the photochemical cycle of this spiropyran. The photochemical cycle of BIPS was theoretically analyzed. The redistribution of the electron density in this cycle was quantitatively described using the differences in NPA of the atomic charges. The most important result of this analysis was the electrostatic mechanism of the approach of Cspiro and oxygen atoms at the fourth stage, which causes further reduction of the CspiroO bond.

Intramolecular excimers of open forms of 2H-benzopyran, 2H- and 3H-naphthopyrans in solution: TD-DFT/DFT analysis

“…45 Similarly, using TD-DFT, one can analyze the possibility of recovering this bond by optimizing the ground state geometry. In our previous works, 46,47 TD-DFT showed a correlation between the calculated recovery/non-recovery of the C spiro –O bond in spiropyrans and experimental data; for BIPS, which tends to be a closed form, the calculated recovery took place, and for 6-nitro-BIPS, which tends to be an open form, there was no recovery in TD-DFT modeling.…”

“…5). Note that the closed form of BIPS spiropyran was recovered under the same modeling of S 1 → S 0 relaxation 46 but not for 6-nitro-BIPS. 47 As can be seen from Fig.…”

“…4). However, this electronic transition is of the π → π* type; 26 therefore, as in the case of spiropyrans, 46,47 the delocalization of σ bond electrons is not direct but is due to the photoinduced redistribution of electron density in aromatic ABC (AB) chromophores (see Fig. 1).…”

Nonadiabatic molecular dynamics simulations for ultrafast photo-induced ring-opening and isomerization reactions of 2,2-diphenyl-2H-chromene

“…Both electronic structure calculations and on-the-fly trajectory surface hopping molecular dynamics simulations for DPC are performed utilizing the TDDFT method with a long-range corrected CAM-B3LYP hybrid functional, 42 which has been recommended to provide optimal results for the photochemical cyclization of a similar benzopyran derivative. 43…”