The Hexaarylbiimidazole ( HABI ) derivatives, which are well-known as photo/thermo/piezo-chromic materials, have been used as polymerization initiators in industry and therefore have been investigated spectroscopically since Maeda and Hayashi prepared them. It has been proposed that the photolysis of the HABI derivative in benzene instantaneously produces a pair of lophyl radicals. This lophyl radical has been proposed to be an initiator for the radical polymerization. In this project, the photo-induced radical pair of the o-Cl-HABI derivative was successfully observed by X-rays using cryotrapping method. When HABI was used as the mother compound, unexpected intermediates were observed. X-ray diffraction analysis elucidated that a pair of HABIs was transformed to a complex composed of two lophyl radicals and piezodimer on irradiation at low temperatures. The piezo dimmer, the existence of which has been assumed spectroscopically as an unstable isomer, was produced via molecular swapping of two photo-induced lophyl radicals with drastic conformational change.