Linear π-conjugated polycyclic compounds consisting of four-, five-, and six-membered rings: benzo[1'',2'':3,4;4'',5'':3',4']bis(cyclobuta[1,2-c]thiophene).

Linear π-conjugated polycyclic compounds, BBCTs, containing linearly annulated 5-, 4-, 6-, 4-, and 5-membered rings were produced via copper-mediated double intramolecular coupling reactions. The absorption spectra and electrochemical results confirmed their moderate optical energy gaps and high HOMO energy levels, respectively. In a crystalline state, the BBCT molecules adopt a herringbone structure, while the methylated molecules form slipped one-dimensional columns. The local and global aromaticity of the new polycyclic compounds is discussed based on the experimental results and theoretical predictions. The present fundamental findings are useful for the further design and synthesis of novel π-conjugated polycyclic compounds containing four-membered rings with potential applications in electronic materials.