C‐Halogenated 9,10‐Diboraanthracenes: How the Halogen Load and Distribution Influences Key Optoelectronic Properties

Abstract

9,10‐Dihydro‐9,10‐diboraanthracenes (DBAs) have low‐energy LUMOs and narrow HOMO–LUMO gaps and are thus attractive electron‐transporting and light‐emitting materials in optoelectronic devices. A systematic series of ten C‐halogenated 9,10‐(Mes)2‐DBAs was synthesized and studied by cyclic voltammetry, UV/Vis absorption and emission spectroscopy, and quantum‐chemical calculations (Mes=mesityl). We probed the influence of the nature of the halogen atoms and the halogen substitution patterns on key optoelectronic properties of the DBAs. All 9,10‐(Mes)2 derivatives can be reversibly reduced at the DBA cores and at electrode potentials between E1/2Red1=−1.84 and −1.26 V (vs. FcH/FcH+). The most bathochromic UV/Vis absorption and the fluorescence emission of each DBA correspond to an ICT transition between the Mes rings and the DBA core. Br substituents lower the DBA LUMO energy and narrow the energy gap to the highest degree along the series F<Cl<Br. Halogen atoms located at 1,4,5,8‐positions are more influential than those at 2,3,6,7‐positions. An increasing fluorine load continuously decreases the LUMO levels and HOMO–LUMO gaps. Colorless octafluoro‐ and tetrafluoro‐DBAs form colored and fluorescent π‐stacked hetero dimers with anthracene in C6H6 solutions and in the solid state. The sterically congested 1,5‐(ThMe)2‐9,10‐(Mes)2‐DBA was prepared in 74 % yield from 1,5‐(Br)2‐9,10‐(Mes)2‐DBA and Me3Sn‐ThMe through a Stille‐type C−C coupling reaction (ThMe=5‐Me‐2‐thienyl).

Introducing Perylene as a New Member to the Azaborine Family

“…As starting material for the synthesis of bis‐BO‐perylenes, we selected the readily available 9,10‐dihydro‐9,10‐diboraanthracene 1,5‐Br 2 DBA(OH) 2 ( 1 ; Scheme ), which already contains all the required heteroatoms and three of the five annulated six‐membered rings. The two remaining C 2 fragments necessary to meet the atom count of perylene were introduced in high yields via Stille‐type coupling reactions using stannyl alkynes ( 2 a – 2 d ) .…”

“…A decisive asset of compound 1 lies in the fact that it can not only be derivatized at its two C−Br functionalities, but also at its BOH units . Indeed, we achieved a clean and quantitative BOH/BN(H)Me exchange by means of MeN(SiMe 3 ) 2 to obtain 4 a , 4 c , and 4 d , which subsequently underwent cyclization via the Au‐mediated hydroamination of the alkynyl substituents to afford the bis‐BN‐perylenes 5 a , 5 c , and 5 d in excellent yields (Scheme ).…”

“…For comparison, the first reductions of perylene and V occur at E 1/2 =−2.26 V (own measurement) and −1.42 V, respectively. The LUMO energy levels of perylene, 3 a , and 5 a , have been calculated from the redox potentials according to the formula E LUMO CV =−4.8 eV− E 1/2 Red1 (FcH/FcH + =−4.8 eV vs. vacuum level) . The trend in the values obtained, that is, E LUMO CV =−2.54 (perylene) < −2.48 ( 3 a ) < −2.18 eV ( 5 a ), is in very good agreement with the trend in the scaled LUMO energies ( E ′ LUMO DFT ) calculated for perylene and the model compounds 3 DFT and 5 DFT , which are devoid of any C‐bonded substituents (Figure ; B3LYP/6‐31G*).…”

Selective access to either a doubly boron-doped tetrabenzopentacene or an oxadiborepin from the same precursor

“…the ESI for full details). 40 Treatment of 1 x with 2 equiv. of (8-halogenonaphth-1-yl)lithium 41,42 furnished syn/anti-isomer mixtures of 2 X,Y in yields between 60% (2 F,Br ) and 89% (2 Br,I ).…”

Practical Synthesis of Ethynyl(phenyl)-λ3-Iodane Using Calcium Carbide as an Ethynyl Group Source

“…In summary, we have developed a safe and inexpensive two-step method for the synthesis of 1a using readily available CaC 2 7 as an ethynyl group source. This method not only provides time-/cost-/labor-saving methodology to prepare unstable ethynyl-λ 3iodane 1, but also serves as an effective approach for synthetically useful but costly bis(stannyl)acetylene 9 (Brend'amour et al, 2018).…”