Double-Site Twisted D-π-D′ Conjugates with Versatile Photophysical Facets for Diverse Optical Applications and Wash-Free Bioimaging of Cancer Cells

Abstract

It is still a conundrum to design a single but simple organic molecule possessing numerous realistic photophysical properties such as mechanofluorochromism, aggregation-induced emission (AIE) properties, solvatochromic DSE-gens (dual-state emissive fluorogens), and viscofluorochromism. Unlike D-π-A, D-π-D′ systems are seldom explored with various applied features. This work finds how a single D-π-D′ indole-anthracene conjugate displays all these properties with real-world applications. Especially, an indole-anthracene-π-phenothiazine conjugate (IAP) appears as a solvatochromic (91 nm shift) DSE-gen that shows the longest 62 nm blueshifted enhanced emission on aggregation and the longest 45 nm blueshifted viscofluorochromic features. Furthermore, IAP adopts a fingertip-pressure-sensitive 35 nm blueshift, while a triphenylamine-linked analogue IAT demonstrates a 23 nm mechanofluorochromic redshift. Conformationally twisted backbone and π-conjugations are judiciously balanced to exhibit these optical features. Such diverse and contrasting photophysical facets are elucidated through experimental and detailed time-dependent density functional theory investigations to meet rational understandings. These fluorophores are utilized as hidden patent fingerprint memory-based platforms and software-assisted comparison studies to identify counterfeiters. Furthermore, highly sensitive fingertip-aided mechanofluorochromic features are useful for inkless security writing. Besides, wash-free bioimaging of robust oral cancer cells (FaDu) could be accomplished satisfactorily in the green (IAT) and orange-red regions (IAP) with a lower probe concentration. The anticancer property of IAT enables visualization of the progressive distortion of the dying cancer cells during wash-free bioimaging.