Synthesis and Response toward External Stimulli of Bithiophene Derivatives Bridged by Spirodienone Structure

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Bithiophene derivtives bridged with a bis (spirodienone) unit were synthesized and characterized. Palladium-catalyzed cross-coupling reactions with bromides afforded a variety of pi-extended derivatives. In these compounds, bond breaking and formation under redox conditions were observed by cyclic voltammetry (CV). Especially, 2,2'-bridged-3,3'-bithiophene derivatives showed significant temperature- and scan rate-dependence on CV. These phenomena indicate the existence of the equilibrium between dispiro-compounds and open-ring biradicals. Furthermore, mechanochromism, N,N-dialkylaminophenyl-substituted 2,2'-bridged-3,3'-bithiophene derivatives showed mechanochromism. During grinding the crystals, the color was changed from yellow to reddish orange, and by exposure to organic solvents, the reddish-orange color was immediately turned back to yellow.