Dual Fluorescence and Aggregation-Induced Emission in Cyclohexadienone Spiro Molecules: Mechanism and Applications

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Planar organic fluorescent dyes often suffer from aggregation-caused quenching (ACQ), limiting their practical use.
• Strong intermolecular π-π interactions in ACQ dyes hinder their performance in concentrated or solid states.

Purpose of the Study:

• To develop novel organic fluorescent molecules that overcome ACQ by exhibiting aggregation-induced emission (AIE).
• To investigate the mechanism behind dual fluorescence in newly designed spiro molecules.
• To explore the sensing capabilities of these AIE-active molecules.

Main Methods:

• Synthesis of cyclohexadienone spiro molecules, including spiro-PT-OMeTAD and its derivatives (spiro-PT-BA, spiro-PT-PA, spiro-PT-MA).
• Spectroscopic analysis to study photophysical properties, including dual fluorescence and aggregation-induced emission.
• Structural analysis to understand the role of the molecular architecture in preventing ACQ.

Main Results:

• The synthesized spiro molecules exhibit AIE and dual fluorescence, originating from locally excited (LE) and twisted intramolecular charge transfer (TICT) states.
• The cyclohexadienone spiro architecture, with its electron-withdrawing carbonyl group and asymmetric spiro geometry, is crucial for promoting TICT and preventing ACQ.
• Derivatives confirmed the universality of the AIE mechanism.
• Spiro-PT-BA demonstrated utility as a polarity-sensitive probe for water content and as a visual temperature sensor.

Conclusions:

• Cyclohexadienone spiro molecules offer a promising strategy to overcome ACQ in organic fluorescent dyes.
• The dual fluorescence mechanism is linked to the unique molecular structure, enabling AIE.
• These AIE-active spiro molecules possess significant potential for developing advanced chemical sensors.