Structural Effects on Photophysical Processes in Saturated Amines. 6. Excited-State Interactions in Piperazine Derivatives

Article abstract of DOI:10.1021/j100208a027

The spectroscopic and photophysical properties of a series of N,N'-bis(alkyl)piperazine derivatives are reported.On the basis of the photoelectron spectrum of N,N'-dimethylpiperazine (I), and the UV absorption spectra of I, N-methylpiperidine (II), 12,14-diazadecahydroanthracene (III), and 13,14-dimethyl-13,14-diazatricyclo<6.4.4.4^2,7>tetradecane (IV), it is concluded that interaction between the N-n orbitals is nearly absent in the ground state.For I and III, however, fluorescence spectral and lifetime data, when compared with monoamine II, indicate the presence of N-N interaction in the lowest excited state. λ_max for I and III are 314 and 315 nm, respectively, while λ_max for II is 292 nm.Lifetimes for I and III are significantly longer relative to II (156 and 148 ns vs. 25 ns).Photophysical data for IV imply that upper state N-N coupling is much less significant than for I and III.A comparison of photophysical data for IV and 1,4-dimethylhexahydro-1,4-diazepine (V) is used to suggest that the piperazine nucleus in IV is twisted, resulting in a less efficient through-bond coupling of the locally excited state with the other N center.The fluorescence properties of substituted piperazines, it is suggested, can be used to infer the conformational structure of the cyclohexane ring.