Real-time measurements of ultrafast electronic dynamics in the disproportionation of [TCNQ]22− using a visible sub-10 fs pulse laser

Abstract

The reduction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) generates a π radical anion, TCNQ−, that dimerizes in methanol solution. This dimer ([TCNQ]22−) exhibits a charge-transfer absorption peak at 620nm and will disproportionate to give TCNQ and TCNQ2− in response to excitation within this charge-transfer band. The present study examined the electronic dynamics of [TCNQ]22− disproportionation. The disproportionation was found to proceed in two steps. Electron transfer, representing the first step, occurred within the 10fs pulse window, followed by the actual dissociation, within 350fs. The emission lifetime of the singlet excited state of TCNQ2− was estimated to be 900fs.