Position-induced differential aggregation behavior with red-shifted emission: A case study of the promising copper ion sensor skeleton-based regio-isomers

AIE-ESIPT active Schiff base luminescent organic materials (LOM) have significant advantages and applications. Still, tuning their emission in the long-wavelength region (>600 nm) while maintaining low molecular mass remains challenging for the research community. Recently, researchers have found excellent capabilities like high CT nature, red-shifted emission, and large stokes shift in meta-fluorophores. However, such studies on the role of meta substitution, especially in the case of AIE-ESIPT active Schiff base LOM, have just been explored. Herein, we have presented a case study on the malonitrile-substituted regioisomers (p-BK and m-BK) based on the SDPA skeleton, a promising copper ion-sensing skeleton. It was found that the emission in m-BK is almost ∼ 50 nm red-shifted with approx. ∼ 200 nm stoke shift, compared to the p-BK. Although changing substituents from para to meta changes the aggregation behavior but, the selectivity remains identical towards copper ions. The practical sensing applicability of both isomers was analyzed in various environments, and bioimaging analysis in HeLa cells were performed to prove the promising nature of the SDPA skeleton. In sum, this case study highlighted the potential of unexplored meta-fluorophores, which can open up new avenues for researchers to create and design new AIE-active LOMs with desired emission wavelengths.