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Abstract Changes in the viscosity of intracellular microenvironments may indicate the onset of diseases like diabetes, blood‐based illnesses, hypertension, and Alzheimer's. To date, monitoring viscosity changes in the intracellular environment remains a challenge with prior work focusing primarily on visible light‐absorbing viscosity sensing fluorophores. Herein, a series of near‐infrared (NIR, 700–1000 nm) absorbing and emitting indolizine squaraine fluorophores (1PhSQ,2PhSQ,SO3SQ,1DMASQ,7DMASQ, and1,7DMASQ) are synthesized and studied for NIR viscosity sensitivity.2PhSQexhibits a very high slope in its Forster‐Hoffmann plot at 0.75 which indicates this dye is a potent viscosity sensor. The properties of the squaraine fluorophores are studied computationallyviadensity functional theory (DFT) and time‐dependent (TD)‐DFT. Experimentally, both steady‐state and time‐resolved emission spectroscopy, absorption spectroscopy, and electrochemical characterization are conducted on the dyes. Precise photophysical tuning is observed within the series with emission maxima wavelengths as long as 881 nm for1,7DMASQand fluorescence quantum yields as high as 39.5 and 72.0 % for1PhSQin DCM and THF, respectively. The high tunability of this molecular scaffold renders indolizine squaraine fluorophores excellent prospects as viscosity‐sensitive biological imaging agents with2PhSQgiving a dramatically higher fluorescence quantum yield (from 0.3 to 37.1 %) as viscosity increases.
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This content will become publicly available on June 4, 2026
Viscosity effects on the chemiluminescence emission of 1,2-dioxetanes in water
The viscosity effects on the emission of two 1,2-dioxetanes with high aqueous quantum yields provide empirical evidence for a stepwise mechanism with viscosity-dependent pathways that reduce chemiluminescence emission.
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- Award ID(s):
- 2155170
- PAR ID:
- 10631869
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Organic & Biomolecular Chemistry
- Volume:
- 23
- Issue:
- 22
- ISSN:
- 1477-0520
- Page Range / eLocation ID:
- 5380 to 5389
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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