Synthesis and properties of push–pull chromophores for second-order nonlinear optics derived from π-extended tetrathiafulvalenes (TTFs)

Novel π-extended tetrathiafulvalene (exTTF) derivatives connected to a p-nitrophenyl electron-accepting unit through a π-conjugated oligoenic spacer () show good second-order optical nonlinearities. The effect of the conjugation length of the oligoenic spacer and the presence of a thiophene ring in the π-conjugated bridge () have been theoretically (PM3) and/or experimentally (EFISH technique) studied. The redox properties of the novel compounds have been investigated by cyclic voltammetry (CV) and the CV data reveal the good donor ability of the exTTF unit. Although the energy of the intramolecular charge-transfer (ICT) band displayed by these compounds and their redox potentials are fairly insensitive to the nature of the conjugated spacer linking the donor and the acceptor moieties, an increase in their second order nonlinear optical responses is observed on increasing the conjugation lengths. Compounds bearing a thiophene ring show a remarkable thermal stability with decomposition temperatures over 400°C. A new series of D-π-A compounds () bearing a 1,3-dithiol-2-ylidene donor unit has also been synthesized and studied.