Phenylpyridyl‐Fused Boroles: A Unique Coordination Mode and Weak B−N Coordination‐Induced Dual Fluorescence

Abstract

Using 4‐phenylpyridine or 2‐phenylpyridine in place of biphenyl, two electron‐poor phenylpyridyl‐fused boroles, [TipPBB1]4 and TipPBB2 were prepared. [TipPBB1]4 adopts a unique coordination mode and forms a tetramer with a cavity in both the solid state and solution. The boron center of TipPBB2 is 4‐coordinate in the solid state but the system dissociates in solution, leading to 3‐coordinate borole species. Compared to its borafluorene analogues, the electron‐accepting ability of TipPBB2 is largely enhanced by the pyridyl group. TipPBB2 exhibits dual fluorescence in solution due to an equilibrium between free TipPBB2 and a weak intermolecular coordination adduct with a second molecule. This equilibrium was further investigated by low‐temperature NMR spectroscopy and photophysical studies. Theoretical studies indicate that the highest occupied molecular orbital (HOMO) of TipPBB2 localizes at the Tip group, in contrast to its borafluorene derivatives, wherein the HOMOs are localized on the borafluorene cores.

Highly Emissive 9‐Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication

“…32 % for FMesB‐Cz and over 45 % for the other two compounds, Figure 4 and Table 1). Relatively long fluorescent lifetimes (134–140 ns in hexane) were observed for all of the compounds, which seems to be an intrinsic behaviour of borafluorenes and was reported by Rupar [58] and Marder [47, 59] and their co‐workers. Almost no solvatochromism was observed in the emission spectra of FMesB‐Cz , but partial quenching was observed in more polar solvents (see Figure S2 in the Supporting Information).…”

“…32 %f or FMesB-Cz and over 45 %f or the other two compounds, Figure 4a nd Table 1). Relativelyl ong fluorescent lifetimes (134-140 ns in hexane) were observed for all of the compounds, which seems to be an intrinsicb ehaviour of borafluorenes and was reported by Rupar [58] and Marder [47,59] and their co-workers.A lmost no solvatochromism was observedi nt he emission spectrao fFMesB-Cz,b ut partial quenching was observed in more polar solvents (see Figure S2 in the Supporting Information). For compound FMesB-Ac,s olvatochromic behaviour was observed as the fluorescencemaximum redshifted from 545 nm in hexane to around6 50 nm in CH 2 Cl 2 solution, with as ignificantly quenched intensity,s imilarly to that observed for the 9-borafluorene compounds reported by Yamaguchi and co-workers.…”

(Hetero)arene-fused boroles: a broad spectrum of applications

“…By employing the electron withdrawing F Mes group as the exo -aryl group on a Bf , the electron accepting ability of FMesBf was enhanced and the reduction potential shifts to −1.93 V. 88 The first reduction potential of phenylpyridyl-fused borole 10b ( E red 1/2 = −1.94 V) 129 is comparable to that of FMesBf , which suggests that the effect of fusing a pyridyl group onto boroles on their reducibility is comparable to that of the exo - F Mes group in 9-borafluorenes. Benzothiophene-fused borole 3c 77 exhibits a first reversible reduction potential of −1.72 V, which is less negative than the electron withdrawing group-functionalized FMesBf and 10b .…”

“…Theoretical and experimental studies suggest that the LUMO energy of these heteroarene-fused boroles are relevant to the antiaromaticity, which also linearly correlates with their Lewis acidities. 105 In contrast to the Yamaguchi group's fused boroles with electron-rich heteroarene(s), more recently, Marder and coworkers 129 switched to the electron-poor pyridine to synthesize phenylpyridyl-fused boroles (Scheme 14). Using 4-phenylpyridine to prepare a fused borole, [10a] 4 was obtained as a white solid and adopts a unique coordination mode, forming a tetramer with a central cavity in both the solid state (X-ray diffraction, Fig.…”

N–B ← N Bridged Bithiophene: A Building Block with Reduced Band Gap to Design n-Type Conjugated Polymers

“…Organoboron chemistry provides new tools to design π-conjugated molecules and polymers. − Jäkle’s, Chujo’s, Pammer’s, Huang’s groups, and our group have made great progress on organoboron A-type building blocks for conjugated polymers. The resulting polymers have been successfully used in OLEDs, OFETs, and OSCs. − ,− Herein, we report a new A-type building block for conjugated polymers, namely, N–B←N bridged bithiophene (BNTzT).…”