Photoinduced Electron-Transfer in 2-tert-Butyl-3-(Anthracen-9-yl)-2,3-Diazabicyclo 2.2.2 octane

摘要

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, photo-induced 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 NN π antibonding orbital. Anthracene ring-centered CC 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.