The main goal of the project is to design and prepare crystals of organic radicals, charge-transfer compounds and metal-organic systems with incorporated radicals, suitable for tuning of the charge transfer and band gap, which can be used to design functional materials. Special attention will be given to the nature of two-electron multicentre covalent bonds (2e/mc or pancake bonds) between the organic radicals and strong pi-hole interactions which involve charge transfer. Our work will involve three classes of compounds: 1) novel radical salts and charge transfer compounds with multicentre bonds, 2) metal-organic systems incorporating radicals and 3) compounds with strong pi-hole interactions. The first phase will be preparation and characterisation of the novel compounds (crystal structure, magnetic, electrical and optical properties). In the second phase we will undertake a thorough experimental study of the 2e/mc bonds and strong pi-hole interactions in selected compounds by X-ray charge density coupled by periodic quantum chemical computations. Study under non-ambient conditions will involve high-pressure and variable-temperature single-crystal X-ray diffraction.