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Direct Imaging of Laser-driven Ultrafast Molecular Rotation

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Published on: February 4, 2017

Dansyl Emits from a PICT Excited State.

Kristen Lum¹, Stephanie M Zielinski¹, Christopher J Abelt¹

¹Department of Chemistry, College of William and Mary, Williamsburg, Virginia 23185, United States.

The Journal of Physical Chemistry. A

|February 2, 2021

Summary

This summary is machine-generated.

Researchers studied how molecular structure affects light emission in dansyl (1-dimethylamino-5-naphthalenesulfonyl) compounds. Constraining the amino group revealed that dansyl likely emits light from a planar state, not a twisted one.

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Area of Science:

Photochemistry
Organic Chemistry
Spectroscopy

Background:

Dansyl (1-dimethylamino-5-naphthalenesulfonyl) derivatives are widely used fluorescent probes.
The excited-state behavior of dansyl, particularly the geometry of its intramolecular charge-transfer (ICT) state, is a subject of ongoing research.
Understanding the photophysical properties of dansyl is crucial for its application in various scientific fields.

Purpose of the Study:

To synthesize and characterize two novel dansyl derivatives with constrained amino groups.
To compare the photophysical behavior (solvatochromism, quantum yields) of these constrained dansyl derivatives with the parent dansyl ester.
To elucidate the emission mechanism of dansyl, specifically whether it involves a planar or twisted intramolecular charge-transfer (PICT or TICT) excited state.

Main Methods:

Synthesis of neopentyl esters of two ring-constrained dansyl derivatives.
Spectroscopic analysis, including UV-Vis absorption and fluorescence emission measurements.
Solvatochromism studies across a range of solvents.
Quantum yield determination.

Main Results:

The constrained dansyl derivatives and the parent dansyl ester exhibited similar solvatochromism and quantum yields.
The constrained derivatives, unable to undergo twisting around the amino group, emit from a planar ICT excited state.
The similarity in photophysical behavior strongly suggests that the parent dansyl ester also emits from a PICT state.

Conclusions:

The photophysical properties of dansyl derivatives are largely independent of amino group twisting.
Dansyl fluorescence emission likely originates from a planar intramolecular charge-transfer (PICT) excited state.
This finding clarifies the long-standing debate regarding the emission mechanism of dansyl derivatives.