Planarized B,N‐diarylated dibenzoazaborine compounds for deep blue fluorescence

Abstract

A series of planarized B,N‐diarylated dibenzoazaborine compounds (5a–5e) in which various functional groups are introduced into the B‐Ph and N‐Ph moieties of nonsubstituted dibenzoazaborine compound (I) were prepared. All compounds exhibit strong low‐energy absorptions at ca. 410–426 nm with a gradual red‐shift depending on the electron‐accepting property of the four substituents (4‐R = 4‐Ph < 4‐Pm < 4‐CNPh <4‐CN) on the B‐Ph ring in 5a–5d. Introduction of an electron‐donating tBu group into the N‐Ph ring further shifts slightly the absorption band toward a lower‐energy region (5e). Importantly, all compounds undergo gradual red‐shifts in the emission leading to deep blue fluorescence for CN‐substituted 5d and 5e. Furthermore, the emissions have narrow full width at half maximum values of ca. 30 nm, high photoluminescence quantum yields (ΦPL ≈ 100%), and small Stokes shifts (11–16 nm). The electrochemical and theoretical studies further support the bandgap control and photophysical properties of compounds.

Highly emissive planarizedB,N-diarylated benzonaphthoazaborine compounds for narrowband blue fluorescence

“…41–45 ppm, similar to those observed for A , confirmed the presence of a trigonal boron atom of the benzonaphthoazaborine skeleton. 25,29…”

“…For this purpose, we recently reported a series of planarized B,N-diarylated dibenzoazaborine compounds, where various electronic modications on the B-and/or N-aryl groups were performed to control the HOMO-LUMO bandgap while preserving the dibenzoazaborine ring core (e.g., R 1 = H; R 2 = aryl in A in Chart 1). 29 Although the emission can be effectively controlled to produce deep blue uorescence at 421-439 nm, we concluded that the bandgap control by modifying the B,N-diaryl groups has a limitation, probably due to the simultaneous electronic effects of the B-or N-aryl substituents on both the HOMO and LUMO levels, partially offsetting the bandgap.…”

“…Following analogous methods for preparing previous B,N-diarylated dibenzoazaborine compounds (A), 25,29 planarized B,Ndiarylated benzonaphthoazaborine compounds (1-5) were synthesized, as illustrated in Scheme 1. To ne-tune the HOMO-LUMO bandgap (E g ), which is relevant to emission control, we made electronic modications at the three positions of the parent B,N-diphenyl benzonaphthoazaborine compound (BzNp, 1), that is, 4-positions of the B-Ph (R 3 ) and N-Ph (R 2 ) rings and the para position to the B atom of the benzoazaborine core (R 1 ).…”

“…We chose electron-donating alkyl groups such as t Bu and Me groups as the substituents and prepared Note that the use of the THF solvent led to high yields (>73%) of silanes (1c and 3c-5c). However, in the ether solvent, which was used to synthesize previous dibenzoazaborine compounds (A), 29 several unknown products, including naphthyl-phenyl coupled species, were formed, consequently resulting in low yields. Next, the silicon-boron exchange reactions of silanes with BBr 3 furnished bromo-azaborine intermediates, which were then subject to in situ reactions with 2,6-di(propen-2-yl) phenyllithium 26 or 4-t Bu-2,6-di(propen-2-yl)phenyllithium to yield arylated benzonaphthoazaborines (1d-5d).…”

“…41-45 ppm, similar to those observed for A, conrmed the presence of a trigonal boron atom of the benzonaphthoazaborine skeleton. 25,29 Photophysical and electrochemical properties To investigate the photophysical properties of compounds, UV/ Vis absorption and photoluminescence (PL) spectra were measured in a toluene solution, and the corresponding spectra are shown in Fig. 1 and S2.…”