Functionalized dibenzoborepins as components of small molecule and polymeric π-conjugated electronic materials

We present the synthesis and characterization of dibenzo[b,f]borepins (DBBs) functionalized at the para and meta position with respect to the boron center in order to understand how regiochemical issues influence photophysical and electrochemical properties. An expanded synthetic repertoire is presented, using palladium catalysis (to perform Stille, Suzuki, Buchwald-Hartwig, and Sonogashira cross-coupling reactions) and lithium-halogen exchange to synthesize a series of extended π-conjugated DBBs. These chemistries are enabled by the use of a sterically bulky Mes* (2,4,6-tri-tert-butylphenyl) group on boron and the inclusion of reactive bromide handles on the DBB core. Photophysical, electrochemical, and computational analyses of these compounds indicate that relative to the protio-DBB the installation of groups at the meta positions decreases the optical band gap while para substitution raises the electron affinity of the system. Thus, both the HOMO-LUMO gap and specific frontier molecular orbital levels can be tuned by the installation of different conjugated substituents.