Buyuktemiz Muhammed, Kılıç Murat, Che Yuanyuan, Zhao Jianzhang, Dede Yavuz
Department of Chemistry, Faculty of Science, Gazi University, Teknikokullar, 06500 Ankara, Turkey.
Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
J Org Chem. 2021 Mar 19;86(6):4547-4556. doi: 10.1021/acs.joc.0c02976. Epub 2021 Mar 3.
Structural and electronic features of ground and excited states of the bis(difluoroboron)-1,2-bis-(pyrrol-2-yl)methylene-hydrazine (BOPHY) fluorophore, a seemingly extended version of the popular 4,4-difluoro-4-bora-3,4-diaza--indacene (BODIPY) fluorophore, are presented. Geometries of S and S electronic states are highly puckered, as confirmed by a combination of density functional theory (DFT), time-dependent (TD)-DFT, CASSCF-PT2, EOM-CCSD calculations and density functional theory-based molecular dynamics (DFT-MD). Packing effects are responsible for planarization in the solid state. Without the network of a solid matrix, planar conformation of BOPHY is an easily accessible transition state of inversion between two puckered conformations and hence solvated BOPHY is suggested to sample the conformational space between the two puckered geometries. The peculiar features of puckering as well as inversion via a planar TS are unaltered with a large range of lateral substitutions. Concentration-dependent electronic absorbance measurements were carried, which showed that the transformation of the low activation energy between the puckered and planar conformations is responsible for the broadening of the absorption spectrum. BOPHY, a four-ring system, is not an electronic extension of the three-ring BODIPY system since the excitation characteristics suggest BOPHY to behave as two electronically unlinked fragments despite the fact that the two subunits are covalently bonded.
本文介绍了双（二氟硼）-1,2-双（吡咯-2-基）亚甲基肼（BOPHY）荧光团基态和激发态的结构与电子特性，它看似是广为人知的4,4-二氟-4-硼-3,4-二氮杂茚（BODIPY）荧光团的扩展版本。密度泛函理论（DFT）、含时（TD）-DFT、CASSCF-PT2、EOM-CCSD计算以及基于密度泛函理论的分子动力学（DFT-MD）共同证实，S和S电子态的几何结构高度褶皱。堆积效应导致固态下的平面化。没有固体基质网络时，BOPHY的平面构象是两个褶皱构象之间易于达到的反转过渡态，因此，溶剂化的BOPHY被认为会在两种褶皱几何结构之间的构象空间中取样。大范围的侧向取代不会改变褶皱以及通过平面过渡态进行反转的独特特征。进行了浓度依赖性电子吸收测量，结果表明，褶皱构象和平面对象之间低活化能的转变是吸收光谱展宽的原因。BOPHY是一个四环体系，并非三环BODIPY体系的电子扩展，因为激发特性表明，尽管两个亚基通过共价键相连，但BOPHY表现为两个电子上不相连的片段。
