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Abstract Strategic incorporation of ameta‐dimethylamino (–NMe2) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m‐NMe2‐LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ~200‐fold decrease in fluorescence quantum yield ofm‐NMe2‐LpHBDI in alcohols (e.g., MeOH, EtOH and 2‐PrOH) supports this GFP‐derived compound as a fluorescence turn‐on water sensor, with large fluorescence intensity differences between H2O and ROH emissions in various H2O/ROH binary mixtures. A combination of steady‐state electronic spectroscopy, femtosecond transient absorption, ground‐state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen‐bonding chain between a solvent –OH group and the chromophore phenolic ring –NMe2and –OH functional groups, wherein fluorescence differences arise from an extended hydrogen‐bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge‐transfer state. The absence of ameta‐NMe2group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without themeta‐NMe2group or with bothmeta‐NMe2andpara‐OH groups locked in a six‐membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors.
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Demonstration of a Stereospecific Photochemical Meta Effect
A fundamental goal of photochemistry is to understand how structural features of a chromophore can make specific bonds within a molecule prone to cleavage by light, or photolabile. The meta effect is an example of a regiochemical explanation for photolability, in which electron donating groups on an aromatic ring cause photolability selectively at the meta position. Here, we show, using a chromophore containing one ring with a meta-methoxy group and one ring with a para-methoxy group, that two stereoisomers of the same compounds can react with light differently, based simply on the three-dimensional positioning of a meta anisyl ring. The result is that the stereoisomers of the compound with the same configuration at both stereogenic centers are photolabile while the stereoisomers with opposite configuration do not react with light. Furthermore, time-dependent density functional theory (TD-DFT) calculations show distinct excitation pathways for each stereoisomer.
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- Award ID(s):
- 1954639
- PAR ID:
- 10319641
- Date Published:
- Journal Name:
- Photochem
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2673-7256
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/photochem2010006
