Thermal Reversion Mechanism of N-Functionalized Merocyanines to Spiropyrans: A Solvatochromic, Solvatokinetic, and Semiempirical Study
Bibliographic record
Abstract
In continuing studies of the effect of solvent and molecular structure on the behavior of photochromic and thermochromic dye molecules, especially spiropyran (SP)−merocyanine (MC) interconversions, we have examined a series of 6‘-nitrobenzoindolinospiropyrans (6-nitro-BIPS) with varying N-functionalities (R = CH 3, CH 2 CH 2 COOH, CH 2 CH 2 CH 2 SO 3 -, CH 2 CH 2 COO-Cholesteryl). The solvent effect was assessed by following the thermal decay of the photochemically ring-opened merocyanine to the spiropyran (MC ⇋ SP) via UV/vis spectroscopy at the λ max of the MC form. It was found that while modification of the N-moiety produced no perturbations in the solvatochromic behavior of these dyes, there was a marked effect on the solvatokinetic behavior. In nonpolar solvents, where the MCs possess predominantly quinoid character (unit central bond order), a constant thermal reversion rate was observed for the MCs with electron-rich N-ligands. This was attributed to electronic and steric interactions between the ligands and the phenoxide moiety. However, in polar solvents the increased zwitterionic character of the MCs (central bond order ∼2) leads to inhibition of the thermal reversion rate for the MCs in this study, independent of N-functionality. The MC ⇋ SP interconversion has also been examined by means of semiempirical calculations. These reveal the lowest energy pathway for conversion of the trans -MC to a cis -MC form via sequential bond rotation of the three central dihedral angles (α, β, and γ). The calculations support the observed solvatokinetic behavior, leading to the assignment of the trans/cis thermal isomerization as the rate-determining step in the overall process.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".