Department of Chemistry
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Item Nucleophilic Substitution Reaction of Alkyl Halides: A Case Study on Density Functional Theory (DFT) Based Local Reactivity Descriptors(ACS, 2002-12-28) Roy, Ram KinkarDensity functional theory (DFT) based local reactivity descriptors, e.g., condensed Fukui function (FF) indices (or condensed local softness) have been tested on the nucleophilic substitution reaction of alkyl halides. As the carbon atom of the C−X (X = Cl, Br, and I) bond (hereafter denoted as CC-X) is the center for nucleophilic substitution, it should emerge as the most preferable site for an attack by a nucleophile (hereafter denoted as Nu-). It was found out when local reactivity descriptors are evaluated from the atomic charges derived from Mulliken population analysis (MPA), the CC-X did not emerge out to be the strongest electrophilic center in majority of cases. However, when these local reactivity descriptors were evaluated by a newly proposed way in which the Mulliken charges on the H-atoms are summed up to those of the heavy atoms to which they are bonded, the results improved significantly. When the reactivity descriptors are evaluated employing the later method and at elongated C−X distances (thus mimicking the situation of the nucleophilic substitution of alkyl halides, in which case the C−X bond is gradually broken), the results show significant improvement. In addition, the present study demonstrates that as the C−X bonds are elongated the global softness values of the systems increase in nearly all cases, thus confirming the validity of maximum hardness principle (PMH).Item Are the Local Electrophilicity Descriptors Reliable Indicators of Global Electrophilicity Trends?(ACS, 2005) Roy, Ram KinkarDensity functional theory based global and local electrophilicity descriptors are used to study the reliability of local electrophilicity values of the strongest electrophilic sites in generating global intermolecular electrophilicity trends. The evaluated values on 15 different organic chlorides show that, for systems having more than one comparatively strong electrophilic site, the local electrophilicity value of the strongest site does not produce a reliable global intermolecular electrophilicity trend. But for systems having one distinctly strong electrophilic site it does. The analytical explanation in favor of the above observation is also provided. Thus, what was argued in an earlier study (Roy, R. K. J. Phys. Chem. 2004, 108, 4934) is established strongly by numerical demonstrations as well as analytical reasoning in the present one.Item Highly Selective Detection of H+ and OH– with a Single-Emissive Iridium(III) Complex: A Mild Approach to Conversion of Non-AIEE to AIEE Complex(ACS, 2015) Roy, Ram Kinkar; Laskar, Inamur RahamanA greenish-blue emissive bis-cyclometalated iridium(III) complex with octahedral geometry was synthesized in a convenient route where a bulky substituted ligand, N1-tritylethane-1,2-diamine ligand (trityl-based rotating unit) (L1), was coordinated to iridium(III) in nonchelating mode, [Ir(F2ppy)2(L1)(Cl)], [F2ppy = 2-(2′,4′-difluoro)phenylpyridine; L1 = N1-tritylethane-1,2-diamine], 1. The purpose of introducing a rotor in 1 was anticipated to initiate aggregation-induced emission (AIE) activity in it. The presence of a secondary amine in L1 has attributed to 1 the ability to sense acids. The mechanism of this change in 1 under acidic medium was explored. A bright yellow emissive complex was formed on exposing 1 to hydroxide ion, which was isolated, characterized, and identified as a new aggregation-induced enhanced emission (AIEE) active complex. The detection limit of hydroxide ion was determined to 126 nM. Ground- and excited-state properties of 1 were investigated using DFT- and TD-DFT-based calculations, and several important aspects of the experimental facts were validated.