Heavy metal organometallic electrophosphors derived from multi-component chromophores

Transition-metal-based phosphorescent materials have recently received considerable academic and industrial attention for fabricating electrophosphorescent organic light-emitting diodes (PHOLEDs), owing to their potential to harness the energies of both the singlet and triplet excitons after charge recombination. Materials suitable for application in PHOLEDs have been actively researched in the past decade and chemical principles have played a crucial role in the evolution of efficient devices for commercialization. More current attention has been paid to the structure–property relationships of phosphorescent small-molecule heavy metal chelate complexes and polymers featuring multiple functional moieties. These organometallic electrophosphors typically possess various hole-transporting, electron-transporting and phosphorescent chromophores with tunable charge-transporting and triplet light-emitting properties. Rational design of multi-component small-molecular metallophosphors, metallodendrimers and metallopolymers aiming at color tuning and multiple functions forms the major focus of this review. In this way, different functional groups can perform specific roles such as photoexcitation, charge transportation and phosphorescence so that highly efficient and simple electrophosphorescent device structures can be developed. The electronic, optical, structural, photo- and electroluminescence properties of these multi-component compounds will be surveyed and discussed. This prominent class of organometallic compounds constitutes an attractive new class of electrophosphors that are thermally and morphologically stable, structurally diverse, and potentially important in optoelectronic applications.