Vanadium dioxide is a thermochromic material that undergoes a semiconductor to metal transitions at a critical temperature of 68 °C. This phase change from a low temperature monoclinic structure to a higher temperature rutile structure is accompanied by a marked change in infrared reflectivity and change in resistivity. This review presents the fundamental chemical principles that describe the electronic structure and properties of solids, and the chronological developments in the theory behind the thermochromic transitions such as, the effects of electron–electron interactions and structural phase changes due to lattice distortions. An extensive discussion and observations on the current understanding of the nature of the semiconductor-to-metal transition exhibited by vanadium dioxide is detailed. The possibility of manipulating the transition temperature by introducing various dopants, additional layers or by size effects into the vanadium dioxide lattice are examined. Thermochromic vanadium dioxide materials may be exploited in areas such as microelectronics, data storage, or intelligent architectural glazing, thus are required to be synthesised as thin films for use in such applications. The numerous synthetic techniques (physical vapour deposition, sol–gel method, pulsed laser deposition, chemical vapour deposition), for making metal oxide thermochromic thin films are described in reference to the production of vanadium dioxide with a particular focus on recent results.

We report a defect-engineering approach to modulate the band gap of zirconium-based metal–organic framework UiO-66, enabled by grafting of a range of amino-functionalised benzoic acids at defective sites. Defect engineered MOFs were obtained by both post-synthetic exchange and modulated synthesis, featuring band gap in the 4.1–3.3 eV range. First principle calculations suggest that shrinking of the band gap is likely due to an upward shift of the valence band energy, as a result of the presence of light-absorbing monocarboxylates. The photocatalytic properties of defect-engineered MOFs towards CO₂ reduction to CO in the gas phase and degradation of Rhodamine B in water were tested, observing improved activity in both cases, in comparison to a defective UiO-66 bearing formic acid as the defect-compensating species.