Impact of Donor Strength on Thermally Activated Delayed Fluorescence in Heptazine-Based Donor–Acceptor Emitters
Bibliographic record
Abstract
Thermally activated delayed fluorescent (TADF) emitters usually feature donor and acceptor units connected in a twisted configuration. This geometry separates the frontier molecular orbitals, resulting in a small energy gap between the lowest singlet and triplet excited states (Δ E ST ), which promotes reverse intersystem crossing (RISC) and subsequent delayed fluorescence. The electron-donating and electron-accepting strengths of the substituents crucially influence the TADF efficiency. Herein, we report the excited state photophysics of heptazine-based TADF emitters by tuning their intrinsic donor strength and environment polarity. Transient absorption and time-resolved fluorescence spectroscopy reveal that with increasing donor strength, the rates of intersystem crossing (ISC) and RISC decrease, contrary to the trends observed for other D–A TADF systems. This behavior results from a larger energy gap between the charge transfer and high-lying locally excited triplet states of these emitters, which weakens the vibronic coupling between them as the donor strength increases.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| 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 | 0.001 |
| 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".