Xerogel-Derived Bis-Imidazole Semiconductors: Chain-Length-Controlled Gelation and Polycrystalline Blue OLED Emission

The development of efficient and stable blue-light emissive organic materials that retain long-range structural order remains a key challenge for optoelectronic applications. Soft materials are a wonderful platform for fabricating various optoelectronic materials as they offer a unique opportunity to combine molecular tunability with a polycrystalline nature. Herein, we report a series of alkyl-substituted 1,4-bis(imidazolyl)benzene gelators designed to investigate the effect of side-chain modulation on supramolecular assembly, xerogel formation, and electroluminescent behavior. Systematic gelation studies reveal that molecules with alkyl chains longer than butyl form robust organogels through a balance of van der Waals and hydrogen-bonding interactions, with xerogels exhibiting polycrystalline features confirmed by X-ray powder diffraction. Structural analyses and computational studies establish that alkylation increases molecular nonplanarity, disrupts face-to-face π···π stacking, and induces pronounced blue shifts in emission relative to the nonalkylated analogue. Incorporation of selected derivatives into the emissive layer of organic light-emitting diodes (OLEDs) demonstrates a clear evolution from bluish-green to pure blue emission, with the butyl and octyl-substituted compound delivering high color purity (CIE 0.16, 0.07; 0.16,0.13), narrow emission bandwidth, and intrinsic electrical and morphological robustness of the xerogel-derived polycrystalline emissive layers. Notably, the butyl derivative exhibits an operational threshold voltage of only 2.8 V, which ranks among the lowest values reported for undoped pristine small-molecule OLEDs. These finding highlights side chain-length-directed supramolecular packing as a powerful design strategy for controlling emission color and accessing ordered soft-material electroluminescence, positioning bis-imidazole xerogels as promising candidates for emerging flexible optoelectronic technologies.