Most planar organic fluorescent dyes are plagued by aggregation-caused quenching (ACQ) due to strong intermolecular π−π interactions, severely limiting their practical applications.

In a study published in Chemistry – An Asian Journal, a research team led by Prof. GAO Peng from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences proposed an innovative molecular design strategy based on cyclohexadienone spiro molecules with aggregation-induced emission (AIE) and unique dual-fluorescence performance.

Researchers adopted spiro-PT-OMeTAD as a model compound to explore the luminescence mechanism. Experimental verification confirmed that the dual emission peaks originated from the locally excited and twisted intramolecular charge transfer (TICT) states, enabling stable, controllable dual fluorescence.

Structural analysis clarified the key role of the cyclohexadienone spiro architecture. The electron-withdrawing carbonyl group in the molecular structure efficiently promoted charge separation and activated the TICT process for effective luminescence.

Besides, the asymmetric spiro geometry provided strong steric hindrance, preventing close molecular stacking and eliminating the ACQ effect. This ingenious structural design perfectly balances charge transfer luminescence and anti-quenching performance.

A series of derivatives, including spiro-PT-BA, spiro-PT-PA, and spiro-PT-MA, were synthesized to verify the universality of the mechanism. All derivatives exhibited similar stable dual-fluorescence characteristics, proving the strategy's applicability for developing high-performance fluorescent dyes.

Benefiting from its polarity-responsive optical properties, spiro-PT-BA was employed as a sensitive probe for trace water detection in tetrahydrofuran and as a visual temperature sensor.

This study provides a novel, universal approach to develop AIE dual-fluorescence materials, offering promising prospects for environmental monitoring, chemical detection, and intelligent optical sensing devices.