Department of Chemistry

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Author: search.filters.author.Roy, Ram KinkarSubject: search.filters.subject.Molecules

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    Screening the Band Shape of Molecules by Optimal Tuning of Range-Separated Hybrid Functional with TD-DFT: A Molecular Designing Approach
    (ACS, 2022-08) Roy, Ram Kinkar
    In the present article we have demonstrated the effectiveness of optimally tuned range-separated hybrid (RSH) functional to determine the electronic transitions from two fluorophore moieties (blue and yellow/orange) within a single white light emitter (WLE). First, the optimally tuned range separation parameter (ω) is calculated for two white emitting fluorophores (W1 and W2) already reported in the literature. The success of the optimally tuned RSH functional ω*B97XD, used in the TDDFT study, encouraged the authors to design eight new single organic white light emitters with frustrated energy transfer between the two individual fluorophore moieties (blue and yellow/orange). The simulated spectra (the band shapes, to be more specific) generated by TDDFT study and outcomes through natural transition orbital (NTO) and natural bond orbital (NBO) studies clearly demonstrate that all the designed eight organic molecules are potential white light emitters and can be synthesized in future.
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    Site of Protonation in Aniline and Substituted Anilines in the Gas Phase: A Study via the Local Hard and Soft Acids and Bases Concept
    (ACS, 1998-08-12) Roy, Ram Kinkar
    In this paper we address the long standing problem regarding the site for gas-phase protonation in aniline and substituted anilines. Our study reveals that DFT-based reactivity descriptors can reproduce the experimentally observed preferable protonation sites. However, it is found that the quantity / , termed “relative nucleophilicity” and a measure of “local polarizability”, produces more reliable results than the local softness, . The problem which sometimes arises in taking / as the reactivity descriptor is also discussed.
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    On the Reliability of Global and Local Electrophilicity Descriptors
    (ACS, 2004) Roy, Ram Kinkar
    The global electrophilicity index w (as defined by Parr et al. J. Am. Chem. Soc.1999, 121, 1992) and local “philicity” index, (as defined by Chattaraj et al. J. Phys. Chem. A2003, 107, 4973) of some carbonyl compounds are evaluated on the basis of Mulliken population analysis (MPA) and Hirshfeld population analysis (HPA) schemes. It is observed that the local electrophilicity indices (i.e., ), extracted from both HPA and MPA based charge, produce reliable intermolecular electrophilicity trends except in one case each. However, the reliability is lost in some cases when w is used. It is also shown both through numerical demonstrations and analytical proof that for generating intramolecular reactivity trends “philicity” index does not provide any extra reliability over local softness or Fukui function values. “Relative electrophilicity” and “relative nucleophilicity”, as defined by Roy et al. (J. Phys. Chem. A 1998, 102, 3746), generate the most reliable intramolecular reactivity (i.e., site selectivity) sequences.
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    Are the Local Electrophilicity Descriptors Reliable Indicators of Global Electrophilicity Trends?
    (ACS, 2005) Roy, Ram Kinkar
    Density 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.