New Charge Transfer Complexes of Self-Assembled TCNQ Derivatives and Picric acid:Synthesis, Characterization, Crystallography and Sensing Application".

Abstract

TCNQ derivatives with primary/secondary amines as substituents are commonly known as diaminodicyanoquinodimethanes (DADQs); a D-π-A molecular system, being zwitterionic are generally stable. Facile and simple charge transfer (CT) complexes were achieved by the reaction between 7,7-bis(N,N-dimethylethylenediamino)-8,8-dicyanodimethane (BMEDDQ),7,7-bis(N,N-diethylethylenediamino)-8,8-dicyanoquinodimethane (BDEDDQ) and picric acid (PA); resulting in BMEDDQ-PA [1] and BDEDDQ-PA [2], followed by effortless crystallization. [1], [2] were characterized by crystallography, spectroscopic and microscopic techniques. Crystallographic investigations revealed extensive H-bonding, π-π stacking, short contacts (< sum of the Van der Waals radii of atoms) among [1], [2] (molecular dipoles) and PA moieties; leading to the supramolecular self-assemblies. Aggregation-caused quenching (ACQ) was observed in solid [1] and [2], marking non-emissive feature, compared to their solutions. BMEDDQ and BDEDDQ were further utilized for PA sensing. The limit of detection (LOD) was ~ 3.0×10-6 M. Field emission scanning electron microscopy (FESEM) manifested varied aggregate formation with increasing PA concentration.  Simplicity in synthesis and analysis accompanied by immediate color change i.e. fast response/fluorescence-based quenching was noteworthy. Moreover, selectivity for PA, good sensitivity in solid as well as solution, and solubility in MeCN: H2O (1:9) mixture accomplish adequacy in detection from water bodies, thus manifest BMEDDQ and BDEDDQ as potential chemosensors for the detection of PA.