Photoinduced electron transfer in 2-tert-butyl-3-(anthracen-9-yl)-2,3- diazabicyclo[2.2.2]octane

Intramolecular photoinduced electron transfer from a hydrazine unit to an aromatic group is studied by resonance Raman spectroscopy and electronic absorption spectroscopy. Substituted hydrazine functional groups have played an important role in studies of electron-transfer reactions, photoinduced intramolecular electron transfer, and of mixed valence. A prototypical compound, 2-tert-butyl-3-(anthracen-9-yl)-2,3-diazabicyclo[2.2.2]octane, that has the hydrazine-to-anthracene charge-transfer band in a region of the visible spectrum suitable for detailed resonance Raman spectroscopy is studied in detail. Excitation profiles are obtained, calculated quantitatively by using time-dependent theoretical methods, and interpreted with the assistance of molecular orbital calculations. Excited-state distortions are calculated. The largest distortions occur on the hydrazine unit; the normal mode showing the largest distortion (659 cm^-1, calculated at 665 cm^-1) involves an out-of-plane C-N-N-C bend consistent with removing an electron from the N-N π antibonding orbital. Anthracene ring-centered C-C stretches also are enhanced, consistent with populating an antibonding π orbital centered on the ring. Excellent fits to all of the excitation profiles and to the absorption band are obtained using one set of excited-state potential surfaces.