Balancing the molecular twist and conformational rigidity in imidazo[1,2-a]pyridines to achieve dual-state emissive (DSE) luminogens for applications in OLEDs 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 emissive 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 design DSE molecules using imidazo[1,2-a]pyridine scaffolds, aiming at enhancing emission performance in the solid and solution states. 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 ΔE_ST values and lifetimes of prompt/delayed components feature the potential TADF properties of these luminogens. Furthermore, as a proof of concept, SK-3 and SK-4 were successfully used in OLED device fabrication. SK-4 shows a good EQE_max of ∼10.00%, while SK-3 shows a reasonable EQE_max of ∼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.