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Title: Excited‐State Dynamics of a meta ‐Dimethylamino Locked GFP Chromophore as a Fluorescence Turn‐on Water Sensor †

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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Journal Name:
Photochemistry and Photobiology
Page Range / eLocation ID:
p. 311-324
Medium: X
Sponsoring Org:
National Science Foundation
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