Optical Trapping of Aggregation-Induced Emission Molecules for Crystallization at the Air/Solution Surface

Area of Science:

• Materials Science
• Optics
• Crystallography

Background:

• Aggregation-induced emission (AIE) molecules exhibit weak luminescence in solution but become highly emissive upon aggregation.
• Crystallization is a key process in materials science, but its early stages (nucleation) are challenging to detect.
• Optical trapping offers precise control over microscopic particles and environments.

Purpose of the Study:

• To investigate optical trapping-induced crystallization (OTIC) of AIE molecules at the air-solution interface.
• To develop a method for studying OTIC using in situ luminescence signals.
• To overcome challenges in detecting nucleation during crystallization.

Main Methods:

• Synthesis of the AIE molecule 4,4'-((1E,1'E)-anthracene-9,10-diylbis(ethene-2,1-diyl))bis(1-methylpyridin-1-ium) iodide (AEMPI).
• Utilizing a 1064 nm continuous-wave (CW) laser for optical trapping at the air-solution interface of an AEMPI solution.
• Monitoring changes in luminescence intensity and crystal growth in situ.

Main Results:

• Initially nonemissive AEMPI aggregates transformed into brightly luminescent crystals under laser irradiation.
• Crystallization restricted molecular motion, activating AIE properties and resulting in red luminescence (640 nm).
• A strong positive correlation was observed between crystal plane area and luminescence intensity.

Conclusions:

• Optical trapping is an effective method to induce and study crystallization of AIE molecules.
• In situ luminescence detection provides a sensitive approach to monitor OTIC and nucleation.
• This technique offers a novel pathway for studying crystallization dynamics.