Tuning of Quinoxaline-Based Molecules for Aggregation-Induced Emission and Room Temperature Liquid Crystallinity

In this work, we report the synthesis of a series of novel compounds based on a 2,3-diquinoxaline core, among which one derivative, QER1, uniquely exhibits both liquid crystalline properties and aggregation-induced enhanced emission (AIEE) in THF-water mixtures. Polarized optical microscopy, differential scanning calorimetry, temperature-dependent X-ray diffraction (for QER1), and thermal gravimetric analysis are employed to study their thermal properties. The thermal study shows that QER1 exhibits the Colh phase at room temperature with a low clearing point. The photophysical studies reveal that the compounds show violet emission in chloroform solutions with λem between 403 and 435 nm. They exhibit a nontypical aggregation-induced emission or AIEE in THF-water mixtures, with the emission intensity increasing to 7.9-fold for QE-F and QER3. Substituting the quinoxaline ring with various groups at the 6 and 7 positions modulates the band gap, with the CN-substituted compound showing the most significant decrease. At the same time, substitution with alkoxy chains exhibits a slight decline. The optimized geometry of all of the derivatives has twisted conformations; however, only QE-CN has spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, while others show significant overlap of orbitals. Our findings reveal a strong correlation between the structure and properties of molecules, resulting in distinct functional properties such as liquid crystalline properties and AIEE in QER1. This compound exhibits a hole mobility of 0.19 × 10⁻⁵ cm² V⁻¹ s⁻¹ at room temperature Colh phase. This work offers a rational strategy for the development of multifunctional materials with potential applications.