Planar, Stair‐Stepped, and Twisted: Modulating Structure and Photophysics in Pyrene‐ and Benzene‐Fused N‐Heterocyclic Boranes

Abstract

Because of their rigidity,polycyclic aromatic hydrocarbons (PAHs) have become as ignificant building block in molecular materials chemistry.F usion or doping of boron into PAHs is known to improve the optoelectronic properties by reducing the LUMO energyl evel.H erein, we reporta comprehensive study on the syntheses, structures, and photophysical properties of an ew class of fused N-heterocyclic boranes (NHBs), pyrene-and benzene-linked in a" Janustype" fashion (2-4, 6-9,and 11). Remarkably,these examples of fused NHBs display fluorescent properties, and collectively their emission spans the visible spectrum.T he pyrene-fused NHBs all display blue fluorescence, as the excitationsa re dominated by the pyrene core. In notable contrast, the emission properties of the benzene-fused analogues are highly tunable and are dependent on the electronicso ft he NHB fragments (i.e.,t he functional group directly bound to the boron atoms). Pyrene-fused 2-4 and 11 represent the only molecules in whicht he K-region of pyrene is functionalized with NHB units,a nd while they exhibit distorted (twisted or stair-stepped) pyrene cores, benzene-fused 6-9 are planar. The electronic structure and optical properties of these materials were probed by computational studies, including an evaluation of aromaticity,e lectronic transitions, and molecular orbitals.

Photochemically- and Thermally-Generated BN- and BNP-Doped Borafluorenate Heterocycles via Intramolecular Staudinger-Type Reactions

“…Amongst boron-containing polycyclic aromatic hydrocarbons (PAH), 9-borafluorenes and their derivatives have become important small-molecule platforms for the construction of highervalue boracycles with unique reactivity trends, electronic features, and photophysical properties. [1][2][3] Research efforts in this regard have engaged a broad array of synthetic chemists interested in fundamental chemical transformations, [4][5][6][7][8][9][10][11] as well as those concerned with uncovering new types of functional materials. 3,[12][13][14][15][16][17][18][19][20][21] Recently, our laboratory synthesized a series of borafluorene radicals, 22 cations, 23,24 and anions, [25][26][27][28][29] all of which rely on the key reaction of a neutral carbon donor ligand (Lewis base) and 9-bromo-9-borafluorene (Lewis acid).…”

Photochemically and Thermally Generated BN-Doped Borafluorenate Heterocycles via Intramolecular Staudinger-Type Reactions

“…Among boron-containing polycyclic aromatic hydrocarbons (PAHs), 9-borafluorenes and their derivatives have become important small-molecule platforms for the construction of higher-value boracycles with unique reactivity trends, electronic features, and photophysical properties. − Research efforts in this regard have engaged a broad array of synthetic chemists interested in fundamental chemical transformations, − as well as those concerned with uncovering new types of functional materials. ,− Recently, our laboratory synthesized a series of borafluorene radicals, cations, , and anions, − all of which rely on the key reaction of a neutral carbon donor ligand (Lewis base) and 9-bromo-9-borafluorene (Lewis acid). Reaction of the 9-carbene-9-borafluorene anion with carbon dioxide (CO 2 ) resulted in the formation of a trioxaborinanone, which releases carbon monoxide (CO) to form a luminescent dioxaborinanone (Figure A) .…”

9-Borafluorenes: Synthesis, Properties, and Reactivity

“…In general, boron heterocycle research has become a rapidly growing field since the turn of the century, − ,,,− and borafluorene research is no exception. At the beginning of the 21st century, conjugated boracycles were recognized for their potential as components in electronic materials and devices with recent research focused on enhancing photophysical properties of these species and developing their utility as reagents. − ,,,,,,− …”

“…Despite being known since 1963, a compilation focused on 9-borafluorenes is absent in the literature . In contrast, their nonannulated analogues, boroles, have been the subject of multiple reviews. ,− Boron heterocycles and boron-doped polycyclic aromatic hydrocarbons have been covered extensively in the secondary literature. − ,− ,,− The aim of this document is to present a comprehensive review on 9-borafluorene species to serve as a resource for research and teaching.…”