Synthesis And Fluorescence Properties Of Bis-BN Naphthooxepine Compounds

Boron-containing?-conjugated materials have received considerable attention in recent years due to their unique optical and structural properties.Substituting one or more C=C units in Polycyclic Aromatic Hydrocarbons?PAHs?with isoelectronic B-N units is a promising way to expanding the PAHsfamily.However,the methods for synthesizing aromatic fused ring compounds containing B-N units are scarce.It is very important to find a simple and effective method for synthesizing BN heteroaromatics with large?-conjugated skeleton.In this paper,a series of novel bis-BN-naphthalene-fused oxepin derivatives were synthesized via a Pd-catalyzed tandem reactionin one step from brominated2,1-borazaronaphthalenes and cis-bis?boryl?alkenes.Crystallographic analysis revealed that bis-BN-naphthalene-fused oxepins feature planar framework.The crystal structure and DFT calculation results disclosed that the C₄B₂O seven-membered ring in this type of compound was not aromatic.The absorption and fluorescence properties of these compounds were investigated in dichloromethane,toluene and DMSO.The electronic and photophysical properties of these novel BN-naphthalene-fused oxepins are quite different to their analogous hydrocarbon system,which shows that the doping of BN atoms has a great impact on the electron distribution,structure,and photoelectric properties of these compounds.Interestingly,dual-fluorescent emissions were observed upon dissolving N-substituted derivatives in DMSO.Tunable emission colors especially for white-light emissions can be achieved by control the concentration in DMSO solution,temperature or proportion of other solvents.This work not only presents a new strategy for the construction of larger BN-doped?-conjugated compounds,but also paves a new way for producing single molecular white-light organic compounds.