Acceptor-induced photoisomerization in small thienothiophene push-pull chromophores

Abstract

Six new push-pull chromophores based on thieno [3,2-b] thiophene were prepared by a facile two step synthesis of extended aldehyde and its subsequent Knoevenagel condensation. Optoelectronic and thermal properties of target chmmophores were tailored by attaching various electron-withdrawing moieties. Variation of the acceptor resulted in tuning of the HOMO-LUMO gap by exclusive altering the LUMO level; the absorption maxima were found within a range of 428-479 nm independently on the used solvent. A reversible E-Z photoisomerization has been observed for the chmmophores with particular electron withdrawing moieties. Whereas irradiation of the chromophores with RoyalBlue LED afforded a dynamic equilibrium of E and Z isomers, the Z-isomer is fully regenerated in the dark. Thus, the switching properties can be easily modulated by attaching proper electron acceptor. According to the performed DFT calculations, both isomers differ in the fundamental (non)linear optical properties.