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A Theoretical Study on Anion Sensing Mechanism of Multi-phosphonium Triarylboranes: Intramolecular Charge Transfer and Configurational Changes

Abstract

The binding selectivity and the recognition mechanism of a series of mono-, di- and triphosphonium substituted triarylboranes: (4-(Dimesitylboryl)-3,5-dimethylphenyl)phosphonium ([Mes2BArP]+, 1), 1,1′-Mesitylboranediylbis(3,5-dimethylphenyl)phosphonium ([MesBArP2]2+, 2) and 1,1′,1″-Boranetriyltris(3,5-dimethylphenyl)phosphonium ([BArP3]3+, 3) where ArP = 4-(H3P)-2,6-Me2-C6H2, for various anions has been investigated by employing the density functional theory (DFT) and time dependent-density functional theory (TD-DFT) methods. Natural population analysis indicates the electrophilic nature of the boron centers in 1-3 for the nucleophilic addition of anions. The calculated free energy changes ( ) reveal that out of CN-, F-, Cl-, Br-,NO3-, CH3COO- and HSO4- only the binding of CN- and F- with 1, 2 and 3 is thermodynamically feasible and spontaneous. In addition, the calculated binding energies reflect that CN- is showing lesser binding affinity than F- both with 1, 2 and 3. The frontier molecular orbital (FMO) analysis reveal that first excited states (S1) of 1-3 are the local excited states with π → π* transition, whereas third excited state (S3), fifth excited state (S5), fourth excited state (S4) and fourth excited states (S4 ) of [Mes2BArP]+F, (1F, the fluoro form of 1), [MesBArP2]2+F, (2F, the fluoro form of 2), [Mes2BArP]+CN, (1CN, the cyano form of 1) and [MesBArP2]2+CN, (2CN, the cyano form of 2) respectively are charge separation states found responsible for the intramolecular charge transfer (ICT) process. The partial configuration changes and ICT induce fluorescence quenching in 1F, 2F, 1CN and 2CN synergistically after an internal conversion (IC) from their respective S3, S5, S4 and S4 to S1.

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Publication details

The article was received on 09 Apr 2017, accepted on 17 May 2017 and first published on 17 May 2017


Article type: Paper
DOI: 10.1039/C7CP02287E
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    A Theoretical Study on Anion Sensing Mechanism of Multi-phosphonium Triarylboranes: Intramolecular Charge Transfer and Configurational Changes

    H. R. Bhat and P. C. Jha, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP02287E

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