Synthesis of bis-BN-Naphthalene-Fused Oxepins and Their Photoluminescence Including White-Light Emission

Abstract

A series of novel bis-BN-naphthalene-fused oxepin derivatives were synthesized via a Pd-catalyzed tandem reaction from brominated 2,1-borazaronaphthalenes and cis-bis­(boryl)­alkenes. X-ray crystallographic analysis revealed that bis-BN-naphthalene-fused oxepins feature a planar framework. The electronic and photophysical properties of the novel BN-naphthalene-fused oxepins were investigated by UV–vis and fluorescence spectroscopies and density functional theory (DFT) calculations, which disclosed the distinct electronic and photophysical properties of the analogous hydrocarbon system. Interestingly, dual-fluorescent emissions were observed upon dissolving N-substituted derivatives 10–14 in dimethyl sulfoxide. Tunable emission colors especially for white-light emissions can be achieved by controlling the ratio of solvents, concentration, or temperature using only a single-molecule compound.

Dithiophene‐Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics

“…The unexpected product C formed through hydrolysis during the workup procedure. Only few further examples of compounds featuring oxadiborepin as a substructure have been reported in the literature [17–20] . The first one, described by Wagner and co‐workers in 2011, was a bisboronic acid anhydride [17] .…”

“…Tian, Xing, Zhu, Cui et al. recently presented BNO‐doped PAHs J , [20] which feature a planar framework. This system is actually described as a bis‐BN‐naphthalene‐fused oxepin.…”

“…Only few further examples of compounds featuring oxadiborepin as a substructure have been reported in the literature. [17][18][19][20] The first one, described by Wagner and co-workers in 2011, was a bisboronic acid anhydride. [17] Recently, they presented the BOB-doped PAH I.…”

“…[18] Due to steric congestion between the annulated benzene rings, this species deviates significantly from planarity. Tian, Xing, Zhu, Cui et al recently presented BNO-doped PAHs J, [20] which feature a planar framework. This system is actually described as a bis-BN-naphthalenefused oxepin.…”

Exciting progress in the transition metal‐catalyzed synthesis of oxepines, benzoxepines, dibenzoxepines, and other derivatives

“…Tian et al in 2019 synthesized bis ‐BN‐naphthalene‐fused oxepine derivatives 25 through palladium‐catalyzed tandem reaction using brominated 2,1‐borazaronaphthslenes 23 and cis – bis (boryl)alkenes 24 (Scheme 7). [ 54 ] In the reaction mechanism, it is assumed that in the first step, the cross‐coupling reaction occurs (Scheme 8). The obtained BN‐doped‐conjugated compounds have shown the luminescent properties in both solution and the solid state with moderate to high quantum yields.…”