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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch

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Substituent-triggered cross-phase inversion of excimer formation.

Hua Zhao¹, Jinshan Xu¹, Wei Chen¹

¹College of Chemistry and Chemical Engineering, Nanchang University, Nanchang 330031, China.

Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy

|June 3, 2026

Summary

Substituent effects can invert excimer formation between solution and solid states. This study reveals how modifying acridine derivatives alters their aggregation-controlled photophysics, guiding the design of novel excimer emitters.

Keywords:

Acridine Discrete dimer Excimer Substituent effect

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Area of Science:

Photochemistry
Materials Science
Supramolecular Chemistry

Background:

Excimer formation mechanisms differ between solution and crystalline states.
The interplay between these mechanisms and substituent effects is not well understood.
Acridine derivatives are known for their photophysical properties.

Purpose of the Study:

To investigate the substituent-triggered inversion of excimer formation across different phases.
To understand the molecular-level factors governing excimer formation in solution and solid states.
To explore the design principles for aggregation-controlled photophysics in acridine derivatives.

Main Methods:

Synthesis of acridine derivatives with varying substituents (unsubstituted, phenyl, 2-methoxy-phenyl).
Photophysical characterization (emission spectra, quantum yield) in solution and crystalline states.
Crystallographic analysis to determine solid-state packing and intermolecular interactions.

Main Results:

In solution, unsubstituted and phenyl-acridines form dynamic excimers, while the methoxy-analogue shows monomeric emission.
In the crystalline state, the methoxy-acridine derivative forms preorganized dimers, yielding strong excimer emission (PLQY 64.8%).
The trend is reversed compared to solution: methoxy-acridine exhibits strong excimer emission, while phenyl-acridine shows partial contribution and unsubstituted acridine shows none.

Conclusions:

Subtle substituent modifications can drastically invert excimer formation propensity across phases.
Directional interactions (Ar-H···O) and π-π stacking in crystals dictate excimer formation.
This work provides insights for designing discrete excimer emitters through substituent and phase control.