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Pablo Rojas¹, Ignacio Aburto¹, Fabián Martínez-Gómez¹

¹Facultad de Química y Biología, Universidad de Santiago de Chile, Av. Bernardo O'Higgins 3363, Santiago 8320000, Chile.

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Summary

This summary is machine-generated.

Brooker's merocyanine (BM) dye shows inverted solvatochromism due to its electronic properties, not E/Z isomerization. Calculations confirm the Z-isomer is thermodynamically unstable, resolving a long-standing question in dye photochemistry.

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Area of Science:

Photochemistry
Spectroscopy
Computational Chemistry

Background:

Brooker's merocyanine (BM) is a key dye exhibiting inverted solvatochromism.
The role of E/Z isomerization in BM's solvatochromism has been debated.

Purpose of the Study:

To investigate the configurational behavior of Brooker's merocyanine (BM) and its protonated form (BMH).
To determine if E/Z isomerization contributes to BM's inverted solvatochromism.

Main Methods:

Selective photoexcitation with steady-state fluorescence spectroscopy.
Proton nuclear magnetic resonance (1H NMR) spectroscopy.
Quantum-mechanics calculations (SCS-MP2/def2-QZVPP) with COSMO-RS solvation models.

Main Results:

The protonated BMH isomerized efficiently under photoexcitation.
No detectable Z-isomer formation was observed for BM.
Calculations showed the Z-isomer of BM is thermodynamically disfavored by ~6 kcal mol-1 in various solvents.
BM exhibited inverted solvatochromism without configurational changes.

Conclusions:

Inverted solvatochromism in BM arises exclusively from the electronic properties of the E-isomer.
E/Z isomerization does not contribute to the observed solvatochromic behavior of BM.