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Developing organic fluorescent molecules with multi-functional properties such as stimuli responses, fluorescence tuning, sensing, white light emission and bioimaging is highly desirable because of their application potential. Herein, we synthesized a triphenylamine (TPA)-based red-emitting ionic fluorophore, (E)-4-(4-(diphenylamino)styryl)-1-alkylpyridin-1-ium (TPA-P), with varied alkyl chain lengths (TPA-P-1 (methyl), TPA-P-7 (heptyl) and TPA-P-14 (tetradecyl)) and utilized them for fluorescence tuning, white light emission, chlorinated solvent sensing and latent fingerprinting applications. TPA-P ionic fluorophores showed anion-dependent tunable solid-state fluorescence from 564 to 671 nm. Single crystal structural studies suggested the anion exchange and modulation of molecular packing in the solid state. Further, TPA-P-1 revealed distinctly different colors and fluorescences towards sodium dodecyl sulphate (SDS) anions in an aqueous medium. Limit of detection (LOD) analysis indicated a sensing response up to 0.8 μM of SDS. TPA-P fluorophores also exhibited sensitive color changes in chlorinated solvents. TPA-P exhibited distinguishable fluorescence in ortho-dichlorobenzene (o-DCB) and meta-dichlorobenzene (m-DCB) isomers. The ionic nature of red-emitting fluorophores was exploited to generate a stable white light-emitting solution by mixing with blue fluorescent polystyrene sulphonate (PSS). CIE chromaticity indicated 0.32, 0.33 color coordinates, which are very close to pure white light emission. The red fluorescence and lipophilic alkyl chain of the TPA-P-14 ionic fluorophore were utilized for latent fingerprinting via powder dusting, which showed well-defined finger marks up to level 3 information. Thus, the quaternization of pyridine nitrogen in TPA π-conjugated fluorophores red shifted the fluorescence, and ionic functionality was further utilized to tailor functional fluorescence properties. [ABSTRACT FROM AUTHOR]

Tetracyanoquinodimethane (TCNQ) is known to react with primary/secondary/certain aromatic amines to generate mono-/di-substituted and cyclized derivatives manifesting optical and non-linear optical material attributes. Interestingly, further functionalization of mono-/di-substituted or cyclized TCNQ derivatives remains unexplored to date. Therefore, herein, we present the synthesis of two cyclized zwitterionic TCNQ derivatives (DDPM [1], DHDPM [2]) which on further reaction with oxalyl chloride ((COCl)2) in the presence of dimethylformamide (DMF) yielded non-zwitterionic aromatic amides, i.e. open-chain benzene derivatives (CDCB [3], CDCHB [4]). Remarkably [1] and [2] exhibited Vilsmeier-Haack type reaction by the combined use of oxalyl chloride and DMF; and the Vilsmeier reagent is produced in situ in a one-pot synthesis. Though the purpose of the said reagent is to introduce a formyl group on the phenyl ring, currently, it reacts with one of the cyano groups rather than attacking the phenyl group. While [1] (Ff = 3.8%) and [2] (Ff = 18.5%) exhibited enhanced fluorescence in the solid state, [3] and [4] displayed it in solution. Crystallographic study revealed a possible role of torsional angle, [1] E 4.241 and [2] E 24.191, for enhanced fluorescence in the solid [2] compared with [1]. [ABSTRACT FROM AUTHOR]