Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ’s possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K+ ion achieved through the selection of 4-(4-aminophenyl)­morpholin-3-one (APM) having considerable π-conjugation and carbonyl (CO) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis­(4-(4-aminophenyl)­morpholin-3-ono)­dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)­morpholin-3-ono)­tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C–H−π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH4Cl, NH4Br, etc.). Currently, the recognition mechanism of K+ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K+ ion with CO and simultaneously cation−π interaction of K+ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation−π interaction occurred between the K+ ion and the phenyl ring (APM) in [2] than in [1] (ΔG binding calculated as ∼16.3 and ∼25.2 kcal mol–1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation−π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline “roses” in [1] and micro/nano “aggregates” in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

Tetracyanoquinodimethane (TCNQ) is known to react with primary/secondary amines to generate mono/di‐substituted TCNQ derivatives resulting in optical (fluorescence) and non‐linear optical characteristics. However, the choice of amine plays a key role in the sequel of certain material attributes. Nevertheless, demonstration of TCNQ derivatives, specifically obtained by reacting TCNQ with simple & small amine side chains of existing anticancer drugs, emerging in dual effect of fluorescence as well as anticancer activity, is not explored so far and has been still existing as a gap in TCNQ related research. Additionally, mono/di‐substituted TCNQ's owning strong fluorescence in solutions (∼10 to 104 order) than their solids are still lacking and are in need to be generated. In this regard, we aimed to synthesize straightforward TCNQ derivatives in single step by reacting TCNQ with specific (simple and small) amines being side chains of existing anticancer drugs (a contemporary design approach) and successfully obtained novel mono/di‐substituted TCNQ derivatives manifesting dual effect of fluorescence and anticancer activity. In this fashion, we have avoided the usage of bulky main moiety of an anticancer molecule, since our aim was not to use the total anticancer drug as such, like in a Pro‐drug preparation, but we intended to use the minimal part of an anticancer drug to invent novel TCNQ derivatives as anticancer active fluorophores. Wavelength of maximum emission for all the five potent molecules was within ∼525 nm‐696 nm. All compounds showed moderate anticancer activity against different cancer cell lines and IC50 values were in the range of 11 to 49 μM, when the synthesized novel compounds were tested in B16F10, MDA‐MB‐231 and A549 cell lines. Henceforth, this study has emanated in the first generation TCNQ derivatives as organic fluorescent anticancer active molecules.

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