Boron, a group 13 element, has several characteristic structural and electronic features: 1) trivalent boron compounds usually adopt a trigonal planar geometry; 2) due to the presence of a vacant p-orbital, effective orbital interaction with pi-conjugated compounds is possible; 3) the presence of a vacant p-orbital is furthermore responsible for high Lewis acidity; 4) the boryl group acts as a pi-electron-accepting group particularly in the excited state. The consequent exploitation of these characteristic features of boron in the molecular design enables us to produce sophisticated pi-functional materials with attractive photophysical and electronic properties. This account article illustrates our systematic studies on the molecular design and the development of functional pi-electron materials using boron as a key element.