Luminescent metal complexes: Diversity of excited states

The photoluminescence of metal complexes has attracted much recent interest since it can be utilized for a variety of applications such as optical sen sors and LEDs. Moreover, the emission behavior provides a probe for the inv estigation of photoreactions including artificial photosynthesis. In this r eview, emitting compounds are classified according to the nature of their e xcited states: metal-centered, ligand-to-metal charge transfer, metal-to-li gand charge transfer, ligand-to-ligand charge transfer, metal-to-metal char ge transfer, ligand-centered (or intra ligand), and intraligand charge tran sfer excited states. Complexes of transition metals (d(n) with n = 0-10), m ain group metals (s(2)),lanthanides and actinides (f(n)) are included in ou r discussion. However, this review does not cover the photoluminescence of metal complexes comprehensively, but illustrates this subject by selected e xamples. The viewpoint is that of a coordination chemist and not of a spect roscopist. Accordingly, molecular complexes which emit under ambient condit ions are preferably chosen.