Tuning the Emission Color of Photoluminescent Molecular Solid-State Materials in the Visible: A Subtle Game between Molecular Structure and Low-Energy Interactions to the Development of Innovative Applications

The chemical nature of luminescent materials is highly diversified, as they can be inorganics, organics, or organic–inorganic hybrid materials. Among the wealth of compounds with various compositions, this Spotlight aims to give an overview of some of the most investigated strategies that are currently developed to tune the color of photoluminescent molecular materials emitting in the visible range. A focus is placed on two families of molecular materials: π-conjugated materials and lanthanide complexes. The ways used to vary the emission color of such materials are illustrated with representative examples taken from a selection of mostly recently published papers, including our own contributions in the field. The relationship between the structure and emission properties is particularly emphasized with an initial description of the main interactions that can occur in these materials, which are π–π stacking and hydrogen bonding, and their influence on both the structural and photophysical properties. Indeed, the presence of intra- or intermolecular interactions can drastically impact the emission properties, whether it is a change in intensity, in color, or both. Then, selected applications for which luminescent molecular materials are currently under investigation or have already reached commercialization are discussed.