Site-selective bimodal absorption and emission of distonic radical cation

摘要

Figure presented 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 _2C~?CH_3) and 1,1-bis(4-methoxyphenyl)ethyl cation (An_2C~+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.