Tojo S, Fujitsuka M, Majima T. Site-selective bimodal absorption and emission of distonic radical cation.
J Org Chem 2010;
75:3618-25. [PMID:
20450220 DOI:
10.1021/jo1003949]
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Abstract
An acyclic 1,4-distonic dimer radical cation (DAE(2)(*+)) was generated from the dimerization of 1,1-bis(4-methoxyphenyl)ethylene radical cation (DAE(*+)) with the neutral molecule (DAE) in solution. The absorption spectrum of DAE(2)(*+) shows bimodal absorption bands with peaks at 350 and 500 nm corresponding to the 1,1-bis(4-methoxyphenyl)ethyl radical (An(2)C(*)CH(3)) and 1,1-bis(4-methoxyphenyl)ethyl cation (An(2)C(+)CH(3)), respectively. Therefore, DAE(2)(*+) in the ground state has the spin and positive charge localized on the 1- and 4-positions, respectively. The bimodal characteristic emissions by the site-selective excitation of radical and cation sites of DAE(2)(*+) were observed at 77 K, showing that the excitation energy is localized on the radical or cation site of DAE(2)(*+) in the excited state. The interaction between radical and cation sites of DAE(2)(*+) in the ground and excited states are discussed on the basis of the steady-state spectroscopic and transient absorption measurements, as well as theoretical calculations.
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