Force-Induced Spiropyran–Merocyanine Interconversion: An Enforced Geometry Optimization Study
- 1Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland
Abstract
Mechanically induced spiropyran (SP)–merocyanine (MC) interconversion was examined using the enforced geometry optimization (EGO) method at the B3LYP/6-311G(d,p) level. The calculations followed a complete mechanical cycle for the SP–CH3 model: tensile opening of the spiro ring, force removal, and subsequent compression. This allowed both SP → MC conversion and recovery of the closed SP structure to be considered within the same computational framework. Across eleven spiropyran derivatives, the first observed opening forces show a clear overall Hammett-like trend, with strongly electron-withdrawing substituents opening earlier and strongly electron-donating substituents opening later. A closer analysis of the H-, NH2-, and Cl-substituted systems showed that C–O cleavage is accompanied by loss of the localized spiro bond, Wiberg bond indices falling to values near zero, charge redistribution, and narrowing of the HOMO–LUMO gap. Calculations in the gas phase and in thirteen COSMO environments revealed a further feature: a low-force geometric reorganization precedes bond cleavage. The solvent also influences which relaxed MC conformer is reached, giving TTC, CTC, CCC, or CCT structures. Neither the calculated ring-opening point nor the final MC conformation is determined solely by the dielectric constant.
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BibTeX
@article{brzyska2026forceinduced,
title = {{Force-Induced Spiropyran–Merocyanine Interconversion: An Enforced Geometry Optimization Study}},
author = {Agnieszka Brzyska},
journal = {International Journal of Molecular Sciences},
year = {2026},
month = oct,
doi = {10.3390/ijms27219767},
url = {https://www.mdpi.com/1422-0067/27/21/9767},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Force-Induced Spiropyran–Merocyanine Interconversion: An Enforced Geometry Optimization Study
AU - Agnieszka Brzyska
PY - 2026
DA - 2026/10/30
JO - International Journal of Molecular Sciences
DO - 10.3390/ijms27219767
UR - https://www.mdpi.com/1422-0067/27/21/9767
AB - Mechanically induced spiropyran (SP)–merocyanine (MC) interconversion was examined using the enforced geometry optimization (EGO) method at the B3LYP/6-311G(d,p) level. The calculations followed a complete mechanical cycle for the SP–CH3 model: tensile opening of the spiro ring, force removal, and subsequent compression. This allowed both SP → MC conversion and recovery of the closed SP structure to be considered within the same computational framework. Across eleven spiropyran derivatives, the first observed opening forces show a clear overall Hammett-like trend, with strongly electron-withdrawing substituents opening earlier and strongly electron-donating substituents opening later. A closer analysis of the H-, NH2-, and Cl-substituted systems showed that C–O cleavage is accompanied by loss of the localized spiro bond, Wiberg bond indices falling to values near zero, charge redistribution, and narrowing of the HOMO–LUMO gap. Calculations in the gas phase and in thirteen COSMO environments revealed a further feature: a low-force geometric reorganization precedes bond cleavage. The solvent also influences which relaxed MC conformer is reached, giving TTC, CTC, CCC, or CCT structures. Neither the calculated ring-opening point nor the final MC conformation is determined solely by the dielectric constant.
SN - 1422-0067
ER -