Synthesis and applications of 1, 8-functionalized heterofluorenes for organic electronics

Heterofluorenes, achieved by substituting the sp³-hybridized carbon of fluorene with oxygen, sulfur, silicon, nitrogen, phosphor etc., are a series of very interesting optoelectronic materials. They have not only many highly effective ways to modify the electronic structures and properties through the particular interactions between the heteroatom and the π-conjugated system, but also show different modification properties at different substitution positions due to the influence of the heteroatoms. 1, 8-Functionalization inspires new properties from widely used materials although the synthesis is always difficult. Owing to the wide spread progress of heterofluorenes and the 1, 8-functionalization strategy, 1, 8-functionalized heterofluorenes have received increasing attention in organic optical and electronic materials and devices recently. Herein, we summarized the basic principles of the molecular design, material synthesis, structure-property relations, and optoelectronic device applications of 1, 8-functionalized heterofluorenes. The different synthetic methods of various 1, 8-functionalized heterofluorenes are reviewed and presented according to different effects of different heteroatoms. Besides, the applications of 1, 8-functionalized heterofluorenes as host materials for phosphorescent organic light emitting diodes, as electroluminescent materials for organic light emitting diodes, as photovoltaic materials for solar cells, and as functional ligands for organic metals are discussed in detail. Finally, the existing key problems and the future development of 1, 8-functionalized heterofluorenes are also outlined and suggested.