Organic Semiconductors: Improving the Design of Bisbenzothiophenes for Low Band Gap Materials

Organic Semiconductors: Improving the Design of Bisbenzothiophenes for Low Band Gap Materials

Jerry Falwell Library, Lower Esbenshade Atrium

3,4,3’,4’-Bibenzo[b]thiophene (BBT) has been reported in the literature some 35 years ago. Back then, doping with iodine was reported to yield some electrical conductivity of the material. After an almost 30 year time gap of no further reports on this class of compounds, this material and its derivatives have recently been revived as potential candidates for organic semiconductors. BBT comprises all necessary basic requirements for a molecule to be an organic semiconductor: it is planar, aromatic, has conjugated double bonds and possesses some oxidative stability. However, its band gap energy (E_g) of 3.5 eV – the energy barrier to promote electron flow – is fairly high, while lower values are desirable. Selective modification of the molecule’s structural design is one major tool for accomplishing this goal. A common route in doing so is by attaching such groups to the BBT molecule that would increase the number of conjugated double bonds. However, in order to actually affect E_g, any such added group must be co-planar with the BBT core. Employing molecular modeling software, molecular geometries and E_g values can be calculated. Based on these data, we present two current design scenarios, both of which increase the number of conjugated double bonds. However, based on the results obtained by molecular modeling, only one design actually shows to be co-planar, thus lowering E_g. Preliminary experimental data will be presented and compared with theoretical data obtained by molecular modeling.