Solid-state photodimerization of 9-substituted acridizinium salts - Selectivity by directional pi stacking

Irradiation 9-donor-substituted acridizinium salts in the solid state gave exclusively the anti-head-to-tail dimers. The regioselectivity of the photo dimerization of the bromo-substituted derivative was independent of the mor phology of the solid sample, and this selectivity is proposed to be the res ult of efficient directional a stacking in the solid state. X-ray structure analysis and solid-state emission spectroscopy are used to characterize th e solid samples.