Fused Tetrathiafulvalene and Benzoquinone Triads: Organic Positive Electrode Materials Based on Dual Redox System

Fused donor-acceptor triads composed of two tetrathiafulvalenes (TTFs) and benzoquinone (BQ) ( 1 ) or naphthoquinone (NQ) ( 2 ) were successfully synthesized. X-ray structure analysis of the bis( n- butylthio) derivative ( 1c ) revealed that the molecules are stacked in a head-to-tail manner. In the cyclic voltammetry, the bis( n -hexylthio)- 1 ( 1d ) exhibits six-pairs of one-electron transfer waves corresponding to the formation of both reduction and oxidation states from -2 to +4. The unsubstituted and bis(methylthio) derivatives of 1 and 2 work as a positive electrode active material for the rechargeable batteries, and several of whose energy densities exceed 800 mWh g -1 . The bis(methylthio)- 2 ( 2b ) also functions as a positive electrode material for the rechargeable sodium ion battery.