Naphthalimide-Appended Squaraine Rotaxanes Exhibit Enhanced FRET Efficiency
Joash Y Lau1, Cassandra C Shaffer1, Hailey S Sanders1
1Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556, United States.
The Journal of Physical Chemistry. A
|December 1, 2025
Summary
This study developed novel fluorescent dyes using 1,8-naphthalimide and squaraine molecules. These dyes efficiently use Förster resonance energy transfer (FRET) for deep-red imaging and sensing applications.
Area of Science:
- Organic Chemistry
- Photochemistry
- Biophysical Chemistry
Background:
- Fluorescent 1,8-naphthalimide dyes are valuable but require red-shifted emission.
- Förster resonance energy transfer (FRET) is key for tuning emission wavelengths.
- There is a need for advanced molecular designs utilizing FRET.
Purpose of the Study:
- To compare 1,8-naphthalimide-squaraine conjugates and rotaxanes as FRET pairs.
- To achieve large pseudo-Stokes shifts and red-shifted emission.
- To develop a practical chemosensor for hydrogen peroxide detection.
Main Methods:
- Synthesis of 1,8-naphthalimide-squaraine conjugates and rotaxanes.
- Spectroscopic analysis to confirm FRET (emission profile, lifetime).
- Investigation of solvent polarity effects on FRET efficiency.
- Development and testing of a boronate-based analogue for hydrogen peroxide sensing in cells.
Main Results:
- Evidence of FRET from 1,8-naphthalimide donor to squaraine acceptor was observed.
- FRET efficiency was enhanced in rotaxane structures compared to simple conjugates.
- Polar solvents increased FRET efficiency in a rotaxane pentad.
- A boronate-based analogue detected hydrogen peroxide in living cells with a 254 nm pseudo-Stokes shift.
Conclusions:
- 1,8-naphthalimide-squaraine rotaxanes are efficient FRET pairs for red-shifted emission.
- Rotaxane encapsulation improves FRET efficiency.
- These systems show promise as sensitive deep-red fluorescent chemosensors.
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