Bhat Haamid R, Jha Prakash C
Computational Chemistry Laboratory, School of Chemical Sciences, Central University of Gujarat , Gandhinagar 382030, India.
Centre for Applied Chemistry, Central University of Gujarat , Gandhinagar 382030, India.
J Phys Chem A. 2017 May 18;121(19):3757-3767. doi: 10.1021/acs.jpca.7b00502. Epub 2017 May 4.
The anion binding selectivity and the recognition mechanism of two isomeric boranes, namely, 4-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline ([p-(MesB)CH(NMe)], 1, where "Mes" represents mesitylene and "Me" represents methyl) and 2-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline ([o-(MesB)CH(NMe)], 2) has been investigated using density functional theory (DFT) and time dependent-density functional theory (TD-DFT) methods. Natural population analysis indicates that the central boron atoms in 1 and 2 are the most active centers for nucleophilic addition of anions. The negative magnitude of free energy changes (ΔG) reveals that out of CN, F, Cl, Br, NO, and HSO only the binding of CN and F with 1 and 2 is thermodynamically feasible and spontaneous. In addition, the calculated binding energies reveal that the CN is showing lesser binding affinity than F both with 1 and 2, while other ions, viz. NO, HSO, Br, and Cl, either do not bind at all or show very insignificant binding energy. The first excited states (S) of 1 and 2 are shown to be the local excited states with π → σ* transition by frontier molecular orbital analysis, whereas fourth excited states (S) of 4-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline cyanide ([p-(MesB)CH(NMe)] CN, 1CN, the cyano form of 1) and 4-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline fluoride ([p-(MesB)CH(NMe)] F, 1F, the fluoro form of 1) and fifth excited state (S) of 2-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline fluoride ([o-(MesB)CH(NMe)] F, 2F, the fluoro form of 2) are charge separation states that are found to be responsible for the intramolecular charge transfer (ICT) process. The synergistic effect of ICT and partial configuration changes induce fluorescence quenching in 1CN, 1F, and 2F after a significant internal conversion (IC) from S and S to S
采用密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）方法，研究了两种异构体硼烷，即4-[双（2,4,6-三甲基苯基）硼基]-N,N,N-三甲基苯胺（[对-（MesB）CH（NMe）]，1，其中“Mes”代表均三甲苯，“Me”代表甲基）和2-[双（2,4,6-三甲基苯基）硼基]-N,N,N-三甲基苯胺（[邻-（MesB）CH（NMe）]，2）的阴离子结合选择性和识别机制。自然布居分析表明，1和2中的中心硼原子是阴离子亲核加成最活跃的中心。自由能变化（ΔG）的负值表明，在CN、F、Cl、Br、NO和HSO中，只有CN和F与1和2的结合在热力学上是可行的且是自发的。此外，计算得到的结合能表明，CN与1和2的结合亲和力均小于F，而其他离子，即NO、HSO、Br和Cl，要么根本不结合，要么结合能非常小。通过前线分子轨道分析表明，1和2的第一激发态（S）是具有π→σ*跃迁的局域激发态，而4-[双（2,4,6-三甲基苯基）硼基]-N,N,N-三甲基苯胺氰化物（[对-（MesB）CH（NMe）]CN，1CN，1的氰基形式）和4-[双（2,4,6-三甲基苯基）硼基]-N,N,N-三甲基苯胺氟化物（[对-（MesB）CH（NMe）]F，1F，1的氟基形式）的第四激发态（S）以及2-[双（2,4,6-三甲基苯基）硼基]-N,N,N-三甲基苯胺氟化物（[邻-（MesB）CH（NMe）]F，2F，2的氟基形式）的第五激发态（S）是电荷分离态，发现它们负责分子内电荷转移（ICT）过程。在从S和S经过显著的内转换（IC）到S后，ICT和部分构型变化协同作用导致1CN、1F和2F中的荧光猝灭
