As a B-B bond-containing polycyclic pi-electron system, a dithieno[3,2-c:2',3'-e](1,2-dihydro-1,2-diborin) derivative and its dianion salts were successfully prepared, and their structures were determined by X-ray crystallography. The neutral. dithieno-1,2dihydro-1,2-diborin has a twisted diborin ring in which both the sigma-TT and p-pi* orbital interactions between the bithiophene pi framework and the B-B bond moiety effectively take place, giving rise to an absorption that is significantly red-shifted compared with that of the parent bithiophene. Upon a two-electron reduction, the dithienodiborin pi framework becomes planar and has a characteristic peripheral. pi conjugation through the B-B bond with 14 pi etectrons. Furthermore, the dianion salts show an intriguing countercation effect on their photophysical, properties, indicative of possible etectronic tuning by the countercations.