Activating [4 + 4] photoreactivity in the solid-state via complexation: from 9-(methylaminomethyl)anthracene to its silver(I) complexes

The [4 + 4] photoreactivity of the anthracene derivative 9-(methylaminomethyl)anthracene (MAMA) has been investigated in solution, gel medium and in the solid state. While quantitative formation of the cyloaddition photoproduct was achieved upon irradiation at λ = 365 nm of ethanol solutions of MAMA, only partial and slow conversion was detected in gels of low molecular weight gelators, and solid-state reactivity was not observed due to the unfavourable relative orientation of the anthracene moieties in the crystal. In hexafluorophosphate, tetrafluoroborate and nitrate silver(I) complexes, however, 9-(methylaminomethyl)anthracene exhibits a more favourable mutual orientation for the aromatic fragments, and [4 + 4] photoreactivity resulted. All compounds were structurally characterized via single crystal and/or X-ray powder diffraction and by Raman spectroscopy; this last technique proved effective in detection of the photoproduct in all solid state complexes.