Tetrathiafulvalenes as π-Electron Donors for Intramolecular Charge-Transfer Materials

Although tetrathiafulvalene (TTF) and its derivatives have been extensively studied for more than 25 years as π-electron donors in intermolecular charge-transfer materials, the intriguing potential of TTF as a donor in an intramolecular sense has only recently been developed. Many versatile, functionalized TTF building blocks are now readily available, and this article will review a range of compounds in which TTF is covalently linked to an electron acceptor moiety by a variety of linking units, sometimes giving rise to an intramolecular charge-transfer (ICT) interaction, which is most frequently manifested in the optical and electrochemical properties. In this context, acceptor subunits include: tetracyano-p-quinodimethane, quinones, electron-deficient aryl groups, pyridinium and bipyridinium units, fullerenes, phthalocyanines, and mesomerically conjugated carbonyl, thiocarbonyl, ester, and related groups. This work paves the way for more systematic and detailed studies of TTF–spacer–A molecules (where A is an acceptor) in which there is increased control of the structural, electronic, optical, and magnetic properties arising from ICT interactions in the ground state, or in the excited state.     

Epitaxial,electro-optically active barium titanate thin films on silicon by chemical solution deposition

Recent progress in the integration of BaTiO₃ thin films with silicon has shown great promise for the development of on-chip photonic devices. However, the highest performing thin films in the literature are deposited by costly and/or complex vacuum techniques. In this study, epitaxial BaTiO₃ thin films are deposited on thin SrTiO₃ template layers on Si(001) from an alkoxide-based chemical solution under atmospheric conditions and yield an effective Pockels coefficient of 27 ± 4 pm/V for an ~85 nm film. Film crystallinity, microstructure, and defect nature are examined by X-ray diffraction and high-resolution transmission and scanning electron microscopy techniques and discussed within the context of the growth method as well as the observed electro-optical response.