A New Aggregation Induced Emission Active Halochromic White Light Emissive Molecule: Combined Experimental and Theoretical Study

Red/near infrared-emissive organic molecules that are aggregation induced emission (AIE) active and having a pH-sensitive core are high in-demand for real-world applications. We have designed and synthesized a far-red to near infrared (NIR) fluorogenic donor–acceptor (D–A) type probe 4-((4-(2-(3,3-dimethyl-3H-indole-2-yl)vinyl)phenyl)(phenyl)amino)benzaldehyde (TPA-SCY), that can undergo protonation with a stronger intramolecular charge transfer. The molecule is pH-sensitive and responds to the acidic behavior of chloroform to produce a unique halochromic white-light emission. Owing to its sensitivity toward pH and its highly emissive nature in the red/NIR region at low pH (approximately 3–5), it accumulates in the intracellular lysosomes and can be used as a live-tracker for lysosomes. Successful application of time-dependent density functional theory with the use of an optimally tuned range-separated hybrid functional reproduces the experimental absorption and emission spectra within the 1–5 nm range (which is not observed when conventional range-separated hybrid functionals are used). Thus, the present work embodies synthesis and photophysical studies (supported by an efficient and highly accurate theoretical tool) of a new AIE active halochromic white light emissive molecule with extensive charge transfer properties and having the ability to behave as a live LysoTracker.