Metallated molecular materials of fluorene derivatives and their analogues

This review covers recent developments in the molecular design and synthesis of metal-based functional materials of fluorenes and their derivatives. Conjugated organic compounds containing metal centers constitute an important class of molecular materials nowadays because of the combined good features of the chemical, electrochemical, electronic and optical properties of the metal groups to those of the organic chromophores. Recently, substituted fluorene derivatives have been extensively explored in the field of optoelectronics and molecular electronics. They are synthetically easily accessible and possess high thermal and chemical stability as well as high emission quantum yields. Such rapidly emerging chemistry of organic-based fluorene derivatives leads us to believe that a related chemistry involving metal centers should present a fascinating subclass and pose potential for the development of new types of novel materials. While there is great scope for chemical modifications of the metal units and structure of the fluorene ring and its substituents in a systematic fashion, these classes of metal-organics can exhibit rich photophysical, redox and structural properties. An understanding of the structure-property relationships of these molecules allows us to establish good model systems in the development of optoelectronic devices, molecular electronics and chemical sensing applications. In this article, homo- and heterometallic systems containing fluorene chromophores and their structural analogues such as carbazoles and diazafluorenes are discussed, and particular attention is paid to chemical reactivities, electronic absorption spectroscopy, photoluminescence and redox behavior, and structural aspects of these metal-organic compounds. The applications that these materials have found in various domains are also highlighted.