Megha Chhatwal

Long range order in Si(100) surfaces engineered with porphyrin nanostructures

Engineering of Si(100) with ordered organic nanostructures represents an advanced method to manufacture hybrid organic/inorganic systems useful for different applications. Well-ordered and densely packed molecules can be obtained by a self-assembly process that depends on directional inter-molecular interactions such as π–π stacking, electrostatic, dipole–dipole or van der Waals interactions, and other more complex forces. Macrocycles are well known to aggregate both in solution and in thin films as a result of some of the above-mentioned interactions. In our study, Si(100) substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer that binds to the surface using the –SiCl3 group and leaves a –CH2Cl group unreacted. The remaining alkyl chloride functionality at the top of the Si(100) substrate allowed additional covalent functionalization with a porphyrin monolayer that resulted in ordered, surface-confined porphyrin assemblies. X-ray photoelectron spectroscopy gave indication of the porphyrin grafting mode. Atomic force microscopy showed a long range order of these nanostructures. Emission measurements confirmed the porphyrin luminescence.

A pyrene-based electropolymerized film as a solid-state platform for multi-bit memory storage and fluorescence sensing of nitroaromatics in aqueous solutions

A polypyrene film of an osmium–terpyridine complex is deposited via anodic electropolymerization on ITO-coated glass electrodes. The optical properties of the film were electrically modulated to generate quintuple absorbance states, making the film a potential molecular alternative to silicon-based static random access memory (SRAM) devices. Moreover, the film could perceive nitroaromatics up to parts-per-million level concentrations in aqueous medium via fluorescence quenching.

Chemically-driven “molecular logic circuit” based on osmium chromophore with a resettable multiple readout

The resettable electro-optical identity of an osmium(II) chromophore has been exploited for integrating miniaturised molecular logic circuits under chemical stimulation. The versatile ‘molecular-probe’ yields multiple outputs using selective stimuli and thus allows precise analysis.

A pyrene-based optical probe capable of molecular computation using chemical input strings

A pyrene-based optical probe for the real-time and regenerative detection of Cu2+ and Fe3+ at parts-per-million (ppm) levels is demonstrated. Moreover, the quantifiable changes in the fluorescence signal induced by chemical inputs viz. Cu2+, Fe3+, H+ and CN− have been exploited to assemble sequential and “four-input” combinatorial molecular logic circuits. A unique “two-way” security lock has also been devised for enhanced information protection at the molecular level.

Gold nanocomposite assemblies using functionalized Ru(II)-polypyridyl complexes

Ru(II)-polypyridyl complexes with various surface anchoring functional groups were prepared at room temperature and utilized as capping and engineering agents to attain surface functionalized gold nanocomposites (Au NCs) with unique morphologies without structure directing templates or functionalized thin films. To corroborate the morphological features obtained by the place-exchange methodology, functionalized Ru(II)-polypyridyl complexes with different surface binding groups such as thiol, ketone, hydrazone and carboxylic acid groups were studied. Au nanocubes, chain and random assemblies were attained upto the microscale level using these Ru(II)-polypyridyl complexes with functional groups acting as Au NP surface binding molecular clips. The morphological and optical changes on the Au NP surface before and after functionalization were studied using electron microscopies (HRTEM with EDS, STEM, SEM), UV-vis and photoluminescence (PL) spectroscopy.

Sensing Ensembles for Nitroaromatics

Explosives can be classified into nitroaromatic compounds (NACs), nitrate esters, nitramines and peroxides. Among these, NACs are at the center of extensive literature studies. NACs are stable and useful in many military operations. However, their stability and explosiveness comes with an ever-increasing danger pertaining to their illegitimate use in terrorist activities. Moreover, NACs are toxic, mutagenic and carcinogenic, and hence they need to be screened out of the environment before their levels reach the admissible limits. The development of economical, efficient, sensitive and real-time sensors for combating the threat of NACs is the greatest need of the hour. In this review, we provide a comprehensive discussion of the recent advancements in the field of NAC sensors.