A density functional theory and spectroscopic study of intramolecular quenching of metal-to-ligand charge-transfer excited states in some mono-bipyridine ruthenium(II) complexes
Bibliographic record
Abstract
The complexes [Ru(NCCH 3 ) 4 bpy] 2+ and [Ru([14]aneS 4 )bpy] 2+ ([14]aneS 4 = 1,4,8,11-tetrathiacyclotetradecane, bpy = 2,2′-bipyridine) have similar absorption and emission spectra but the 77 K metal-to-ligand charge-transfer (MLCT) excited state emission lifetime of the latter is less than 0.3% that of the former. Density functional theory modeling of the lowest energy triplet excited states indicates that triplet metal centered ( 3 MC) excited states are about 3500 cm −1 lower in energy than their 3 MLCT excited states in both complexes. The differences in excited state lifetimes arise from a much larger coordination sphere distortion for [Ru(NCCH 3 ) 4 bpy] 2+ and the associated larger reorganizational barrier for intramolecular electron transfer. The smaller ruthenium ligand distortions of the [Ru([14]aneS 4 )bpy] 2+ complex are apparently a consequence of stereochemical constraints imposed by the macrocyclic [14]aneS 4 ligand, and the 3 MC excited state calculated for the unconstrained [Ru(S(CH 3 ) 2 ) 4 bpy] 2+ complex (S(CH 3 ) 2 = dimethyl sulfide) is distorted in a manner similar to that of [Ru(NCCH 3 ) 4 bpy] 2+ . Despite the lower energy calculated for its 3 MC than 3 MLCT excited state, [Ru(NCCH 3 ) 4 bpy] 2+ emits strongly in 77 K glasses with an emission quantum yield of 0.47. The emission is biphasic with about a 1 μs lifetime for its dominant (86%) emission component. The 405 nm excitation used in these studies results in a significant amount of photodecomposition in the 77 K glasses. This is a temperature-dependent biphotonic process that most likely involves the bipyridine-radical anionic moiety of the 3 MLCT excited state. A smaller than expected value found for the radiative rate constant is consistent with a lower energy 3 MC than 3 MLCT state.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.000 | 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 teacher head, 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".