Tuning the Electronic Properties of Nonplanar exTTF-Based Push?Pull Chromophores by Aryl Substitution

摘要

A new family of π-extended tetrathiafulvalene (exTTF) donor−acceptornchromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTFsubstitutednalkynes and subsequent cycloreversion. X-ray data and theoretical calculations,nperformed at the B3LYP/6-31G** level, show that the new chromophores exhibit highlyndistorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-ndiene (TCBD) units. The electronic and optical properties, investigated by UV/visnspectroscopy and electrochemical measurements, are significantly modified when thenTCBD acceptor unit is substituted with a donor phenyl group, which increases the twistingnof the TCBD units and reduces the conjugation between the two dicyanovinyl subunits.nThe introduction of phenyl substituents hampers the oxidation and reduction processesnand, at the same time, largely increases the optical band gap. An effective electronicncommunication between the donor and acceptor units, although limited by the distortednmolecular geometry, is evidenced both in the ground and in the excited electronic states.nThe electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the nearinfrared.