Synthesis and fluorescence properties of butadiyne-linked linear and cyclic carbazole oligomers

Butadiyne-linked linear and cyclic carbazole oligomers were successfully synthesized. The intensity of the emission band in the 0-0 band of the highly planar macrocyclics decreased compared to that of the 0-1 band. Contrary to this, for larger macrocycles having reduced planarity, the intensity of the emission of the 0-0 band increased as in the cases of the linear compounds. This suggests that the emission color of the π-conjugated molecule can be controlled not only by the difference between the cyclic and chain structures but also by the control of the planarity, and is expected to be a new principle for molecular design in the development of fluorescent materials. Planar macrocycles exhibite blue emission whereas flexible ones emit near white light.