Development of a Multifunctional Aggregation-Induced Emission-Active White Light-Emissive Organic Sensor: A Combined Theoretical and Experimental Approach

Abstract

A far-red to near-infrared (NIR) “aggregation-enhanced emission” (AEE)-active donor–acceptor (D–A)-type probe (denoted as IMZ-CN) is designed and synthesized. The probe IMZ-CN is designed rationally using the quantum mechanical gap tuning (highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap, i.e., ΔEg) approach. The probe is tethered with two different functionalities, i.e., dicyanovinyl (DCV) and benzimidazole (IMZ), which effectively lower the value of ΔEg and cause emission in the far-red to near-infrared region. Furthermore, it selectively detects cyanide (CN–) and fluoride (F–) ions by turn-on emission in pure water without interference between each other. Apart from CN–/F– sensing, the probe (IMZ-CN) is also sensitive toward the acidic environment due to the presence of potential basic nitrogen on the benzimidazole unit. The binding of CN–/F– induces a blue shift in the electronic spectra of IMZ-CN, whereas an acidic environment (e.g., the change in pH from 7 to 2.3) causes red-shifted emission (∼60 nm). Interestingly, IMZ-CN displays a nearly pure white emission during the course of the aggregation-enhanced emission (AEE) mechanism study in the PEG–water binary mixture (99%) with CIE coordinates (0.30, 0.33). The mechanisms behind the emission of white light and the anion-binding/sensing applications (photophysical properties of the probe) are supported by quantum mechanical calculations [using “frontier molecular orbitals” (FMO), “time-dependent density functional theory” (TD-DFT), and “natural transition orbital” (NTO) calculations]. As this multifunctional probe IMZ-CN interacts with CN–, F–, H+, etc., the reactivity parameters [e.g., global chemical hardness (η), global electrophilicity (ω), etc.] were calculated by applying the concept of “density functional reactivity theory” (DFRT) to validate its reactivity.