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, <b>QER1</b>, 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 <b>QER1</b>), and thermal gravimetric analysis are employed to study their thermal properties. The thermal study shows that <b>QER1</b> exhibits the Col_h phase at room temperature with a low clearing point. The photophysical studies reveal that the compounds show violet emission in chloroform solutions with λ_em 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 <b>QE-F</b> and <b>QER3</b>. 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 <b>QE-CN</b> 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 <b>QER1</b>. This compound exhibits a hole mobility of 0.19 × 10^-5 cm² V^-1 s^-1 at room temperature Col_h phase. This work offers a rational strategy for the development of multifunctional materials with potential applications.