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

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., Delta E-g) approach. The probe is tethered with two different functionalities, i.e., dicyanovinyl (DCV) and benzimidazole (IMZ), which effectively lower the value of Delta E-g 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 (similar to 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 (eta), global electrophilicity (omega), etc.] were calculated by applying the concept of "density functional reactivity theory" (DFRT) to validate its reactivity.