Magneto-Fluorescent Microrobots with Selective Detection Intelligence for High-Energy Explosives and Antibiotics in Aqueous Environments

Fluorescence-based sensing is a straightforward and powerful technique with high sensitivity for the detection of a wide range of chemical and biological analytes. Integrating the high sensing capabilities of fluorescent probes with wireless navigation systems can enable the extension of their operational range, even in challenging scenarios with limited accessibility or involving hazardous substances. This study presents the development of molecularly engineered magneto-fluorescent microrobots based on the push-pull quinonoids by incorporating magnetic nanoparticles using a reprecipitation approach with the aim of detecting high-energy explosives and antibiotics in aqueous environments. The magnetic components in the microrobots offer remotely controlled navigability toward the intended target areas under the guidance of external magnetic fields. Upon interactions with either explosives (picric acid) or antibiotics (tetracycline), the microrobots' intrinsic fluorescence switches to a "fluorescence off" state, enabling material-based intelligence for sensing applications. The molecular-level interactions that underlie "on-off" fluorescence state switching upon engagement with target molecules are elucidated through extensive spectroscopy, microscopy, and X-ray diffraction analyses. The microrobots' selectivity toward target molecules is achieved by designing microrobots with amine functionalities capable of intermolecular hydrogen bonding with the acidic hydroxyl group of picric acid, leading to the formation of water-soluble charge transfer picrate complexes through proton transfer. Similarly, proton transfer interactions play a key role in tetracycline detection. The selective fluorescence switching performance of microrobots in fluidic channel experiments illustrates their selective sensing intelligence for target molecules in an externally controlled manner, highlighting their promising characteristics for sensing applications in real-world scenarios.

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

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-dicyanoquinodimethane (BMEDDQ),7,7-bis (N,N-diethylethylenediamino)-8,8-dicyanoquinodimethane (BDEDDQ) and picric acid (PA) each respectively; resulting in BMEDDQ-PA [1] and BDEDDQ-PA [2], further followed by effortless purification by crystallization. Acquired CT complexes (CTs) [1], [2] were characterized thoroughly by crystallography, spectroscopic and microscopic techniques. Crystallographic investigations revealed extensive H-bonding, π-π stacking, short contacts ( Collapse

Key Words

• Charge transfer complexes
• Crystallography
• Fluorescence quenching
• PA sensing in solutions
• Spectroscopy

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MESH Headings Collapse

Grants

• Central Analytical Laboratory (CAL)
• SR/FST/CSI-240/2012 DST-FIST
• Department of Chemistry
• BITS-Pilani Hyderabad Campus
• HRMS
• DST-FIST
• SR/FST/CS-I/2020/158
• BITS

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Affiliation(s)

Anuradha Mohitkar Department of Chemistry, Birla Institute of Technology and Science, Pilani-Hyderabad Campus, Jawahar nagar, Kapra Mandal, Medchal, Malkajgiri District, Hyderabad, 500078, Telangana, India
Jayanty Subbalakshmi Department of Chemistry, Birla Institute of Technology and Science, Pilani-Hyderabad Campus, Jawahar nagar, Kapra Mandal, Medchal, Malkajgiri District, Hyderabad, 500078, Telangana, India

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Efficient Standalone Flexible Small Molecule Organic Solar Cell Devices: Structure-Performance Relation Among Tetracyanoquinodimethane Derivatives

Currently, very few dicyano and tetracyanoquinodimethane (TCNQ) based molecules are utilized as active layers, sandwiched between the electron and hole transport layer in organic solar cell (OSC) devices. Nevertheless, simple mono- and disubstituted TCNQ derivatives as exclusively active layers are yet unexplored and provide scope for further investigation. In this study, TCNQ derivatives with varying amine substituents, namely, AEPYDQ (1), BMEDDQ (2), MATBTCNQ (3), and MITATCNQ (4), were explored as efficient standalone, flexible, all small molecule OSC devices. Particularly, 1 resulted in the highest device efficiency of 11.75% with an aromatic amine, while 2 possessing an aliphatic amine showed the lowest power conversion efficiency (PCE; 2.12%). Notably, the short circuit current density (JSC) of device 1 increased from 2 mA/cm2 in the dark to 9.12 mA/cm2 under light, indicating a significant boost in the current generation. Further, 1 manifested more crystallinity than others. Interestingly, 4 exhibited a higher PCE (5.90%) than 3 (PCE is 2.58%), though 3 is disubstituted with an aromatic amine, probably attributed to the electron-withdrawing effects of the -CF3 and -CN groups in 3 reducing the available π-electron density for stacking. Therefore, this study emphasizes crystallinity, significantly on the PCE, offering insights into the design of many such efficient OSCs.

Unprecedented transformation from cyclized zwitterionic oxazolidine derivatives to corresponding non-zwitterionic aromatic amides via Vilsmeier reagent in a one-pot reaction: optical property and crystallography

In situ formation of iminium intermediate in the conversion of zwitterionic oxazolidine derivatives to aromatic amides resulting in contrasting optical properties.

Distinct Tetracyanoquinodimethane Derivatives: Enhanced Fluorescence in Solutions and Unprecedented Cation Recognition in the Solid State

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.

Mechanical control of molecular aggregation and fluorescence switching/enhancement in an ultrathin film

Optical responses of molecular aggregates and assemblies are often different from that of the individual molecules. Self-assembly approaches provide little physical control on the extent of aggregation. Mechanical compression of amphiphilic molecules (with chromophore/fluorophore head groups) at the air-water interface, followed by transfer as Langmuir-Blodgett (LB) films, should prove to be an elegant route to molecular assemblies with systematically tunable aggregation and optical responses. This concept is demonstrated using monolayer LB films of a diaminodicyanoquinodimethane (DADQ)-based amphiphile fabricated at different surface pressures. Films deposited above a threshold pressure exhibit a strong blue-shift in the absorption and fluorescence relative to those deposited below; computational investigations suggest that this is due to the formation of 2-dimensional close-packed assemblies. Significantly, the blue emission of the films deposited above the threshold pressure increases with compaction, demonstrating aggregation-induced fluorescence enhancement in ultrathin films, a phenomenon well-established in crystals and nanocrystals of selected classes of molecules including the DADQs. The sharp contrast with aggregation-induced fluorescence quenching observed with most dye molecules is illustrated by a parallel investigation of LB films of a hemicyanine-based amphiphile. The present study illustrates the efficacy of simple mechanical compression and the LB technique in fabricating ultrathin films with tailored supramolecular assembly and optical responses.