Balancing the Molecular Twist and Conformational Rigidity In Imidazo[1,2-a]pyridine to achieve Dual-State Emissive (DSE) Luminogens for Applications in OLED and Cell-imaging

Abstract

The need for fluorophores that could be emissive in both solution and solid states has led to the development of Dual State Emissive (DSE) materials which bridge the gap between the ACQ and AIE and offer omnipresent emission. However, designing DSEgens requires a meticulous balance of the emission and non-radiative pathways in both states. Despite some advancements, achieving dual-state emission deals with challenges in synthesis, scalability, and application. This study focuses on balancing the molecular twist and electronic rigidity to designing DSE molecules using imidazo[1,2-a]pyridine scaffolds aiming towards enhancing emission performance in the solid as well as solution state. Six novel D-A-structured imidazo[1,2-a]pyridine-arylketone conjugates (SK-1 to SK-6) were synthesized, incorporating bulky aryl rotors like triphenylamine (TPA) and aryl ketones (-COPh) to achieve twisted configurations and impact electronic structures. Experimental results showed promising features, with SK-3 and SK-4 displaying DSE effects, and SK-2 and SK-5 exhibiting AIE characteristics with good PLQY values. The luminogens demonstrated high thermal stabilities, stable electrochemical properties, and effective cell imaging capabilities with low cytotoxicity. The calculated ΔEST values and lifetimes of prompt/delayed components confirmed TADF properties. Further, as a proof of concept, SK-3, and SK-4 were successfully used in OLED device fabrication. SK-4 shows a good EQEmax ̴ 10.00% while SK-3 shows a reasonable EQEmax̴ 6.4% with superior efficiency roll-off as compared to SK-4. This study highlighted the importance of balancing molecular distortion and conjugation in designing multifunctional DSE molecules for optoelectronics and bioimaging applications.