H. Ihmels et al., Solid-state photodimerization of 9-substituted acridizinium salts - Selectivity by directional pi stacking, MOLEC CRYST, 356, 2001, pp. 433-441
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.