The spectroscopic and photochemical properties of a family of α-oxo[1.n]Paracyclophanes (8-12) for n = 8–12, respectively) have been investigated. Compared to a model structure possessing a nominal T1(nπ*) state (4,4'-dimethylbenzophenone, DM-BZ), photochemical and photophysical evidence is presented that the nπ* character of T1 decreases as the cyclophane ring size decreases. For example, the rate constants for hydrogen atom abstraction from 1,4-cyclohexadiene in acetonitrile are 1.6 X 108, 0.93 X 108, 0.30 X 108, 0.06 X 108, and 0.04 X 108M-1s-1 for triplet 12–8, respectively, a result consistent with decreasing nπ* character and decreasing reactivity toward hydrogen atom abstraction with decreasing value of n. The spectroscopic properties (vibrational structure of the phosphorescence spectrum, phosphorescence lifetime, phosphorescence excitation spectra, triplet-triplet absorption spectra) also vary in a manner consistent with decreasing nπ* character as the cyclophane ring size decreases.
ASJC Scopus subject areas
- Colloid and Surface Chemistry