New aspects of vapochromic metal complexes: Cooperative phenomena in functions and structures

The latest trends in vapochromic materials that exhibit reversible color changes in response to gas or vapor are reviewed. Since the end of the 20th century, studies on vapochromic materials have significantly increased for environmental sensing, particularly those accompanied by the luminescence. In addition to the diversity of materials, vapochromic multifunctional systems that exhibit additional functions, such as conductivity and magnetic properties along with color and/or luminescence change by vapor, would be more attractive. In this context, recent developments in multifunctional vapochromic systems are discussed. Systems exhibiting single-crystal to single-crystal transformations are reviewed because these provide useful information on the structural dynamics, which is essential for understanding vapochromic phenomena.