Multi-stimuli distinct responsive D–A based fluorogen oligomeric tool and efficient detection of TNT vapor

Abstract

It is highly demanding to develop a fluorescence-based multi-stimuli responsive material. Herein, we reported an oligomeric network labeled P1, composed of heterocyclic triazine as the π-electron acceptor (A) connected directly with the π-electron rich donor (D) triphenylamine (TPA). The observed difference in the electron density of the D–A moieties of P1 supports the response with various solvent polarities and exhibits solvatochromic property. P1 shows the ability to sense the trinitrotoluene (TNT) explosive material by observing the quenching effect on the emission. It detects TNT from an aqueous solution down to the femtomolar level (10⁻¹⁵ M). The observed detection limit is 698 ppb in the vapor phase. The paper-based sensing ability of TNT by P1 was verified. The D–A network structure and available active protonic sites in the oligomer (P1) make it highly sensitive to both Brønsted and Lewis acids in liquid and vapor phases. P1 exhibited a bathochromic shifted emission upon exposure with trifluoroacetic acid (TFA) and boron trifluoride etherate by 108 and 94 nm in the solution phase and 97 nm and 35 nm in the vapor phase, respectively. Furthermore, P1 exhibits mechanofluorochromism (MFC) with unusual hypsochromic shifting (555 to 535 nm) with enhanced emission intensity upon grinding. It is further noted that the same probe shows a distinct emissive response with different stimuli, i.e., quenching towards TNT sensing, bathochromically shifted emission for acidochromism, hypsochromically shifted emission against MFC behavior, and polarity-dependent emission observed for solvatochromism.