Polymorphism and Light-Driven Forward Movement of TPE Derivative Micro-Crystal due to ArH-pi Interactions Difference.

Area of Science:

• Materials Science
• Chemistry
• Optoelectronics

Background:

• Aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) are contrasting luminescence phenomena.
• Typically, a single molecule exhibits either AIE or ACQ, but not both simultaneously.

Purpose of the Study:

• To investigate a TPE derivative (TAP-TPE) capable of forming both AIE and ACQ crystals.
• To elucidate the structural and electronic factors governing these dual luminescence behaviors.
• To explore the potential applications of these unique crystalline materials.

Main Methods:

• Synthesis of TAP-TPE, a tetraphenylethylene derivative.
• Crystallization to obtain distinct AIE and ACQ crystal forms.
• X-ray diffraction and crystallographic analysis to study intermolecular interactions (ArH-π).
• Theoretical calculations (electron density analysis) to understand emission mechanisms.
• Photochromism and photo-actuation experiments under UV irradiation.

Main Results:

• TAP-TPE forms both AIE and ACQ crystals with different ArH-π interaction strengths and geometries.
• Stronger ArH-π interactions in ACQ crystals correlate with significant electron density changes and intermolecular electron transfer.
• One crystal form exhibits rapid photochromism, suitable for anti-counterfeiting.
• Photochromic crystals demonstrate light-driven forward rolling movement, acting as photo-actuators.

Conclusions:

• The study demonstrates the simultaneous occurrence of AIE and ACQ in a single molecule through distinct crystal packing.
• Intermolecular ArH-π interactions play a crucial role in determining luminescence properties and electron transfer.
• The photochromic and photo-actuating properties of the crystals present novel opportunities for light-driven devices and security materials.