Fluorescence and Electronic Action Spectroscopy of Mass-Selected Gas-Phase Fluorescein, 2′,7′-Dichlorofluorescein, and 2′,7′-Difluorofluorescein Ions
Bibliographic record
Abstract
2',7'-Dichloro- and 2',7'-difluorofluoresceins are superior alternatives to underivatized fluorescein. Although several studies characterizing their condensed-phase photophysical properties have been reported, little is known about their intrinsic characteristics. Here, the gas-phase properties of three charge states of each fluorescein are characterized using a quadrupole ion trap mass spectrometer which has been modified for spectroscopy. Electronic action spectra, constructed by monitoring the extent of photodissociation as a function of excitation wavelength, indicate that the gaseous dianions and cations resemble their solution-phase counterparts. In contrast, a large shift in the electronic action spectra of the monoanions indicates the presence of a different tautomer in the gas phase than that present in solution. The gaseous monoanion is deprotonated on the xanthene ring, rather than being deprotonated on the pendant group as found in soluion. The dianions and cations do not emit detectable fluorescence in the gas phase. In contrast, the monoanions do fluoresce, but the emission intensity is low and the spectra are broad. This work illustrates the effect of halogenation on the intrinsic properties of the dyes and provides useful fundamental understanding that promises to aid the development more robust fluorescent dyes.
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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".