Light-Emitting Self-Assembled Materials Based on d(8) and d(10) Transition Metal Complexes.

Photoluminescence Properties of Multinuclear Copper(I) Compounds.

Relatively little attention has been paid to metal ions with the nd[sup 10] and nd[sup 10](n+1)s[sup 2] (i.e., [open quotes]s[sup 2][close quotes]) configurations. In combination with various anionic and neutral ligands, these metal ions form a wide variety of cluster compounds, some of which have been known to be luminescent when irradiated with ultraviolet light. Prominent examples of this family are cuprous iodide clusters such as Cu[sub 4]I[sub 4]-(py)[sub 4] (1, py = pyridine), which shows [open quotes]luminescence thermochromism[close quotes]; that is, they display bright emissions with colors markedly dependent on the temperature. Here the authors present an overview of recent studies carried out both independently and jointly in the authors' laboratories focusing upon the remarkably rich, but relatively unexplored, photochemical and photophysical properties of various tetra-and hexanuclear d[sup 10] and s[sup 2] metal ion clusters in solution. 74 refs., 4 figs., 2 tabs.

/pdf/photochemical-and-photophysical-properties-of-tetranuclear-vka15ses5b.pdf

Photochemical and photophysical properties of tetranuclear and hexanuclear clusters of metals with d10 and s2 electronic configurations

Cu(I) complexes and clusters are the largest class of compounds of relevant photochemical and photophysical interest based on a relatively abundant metal element. Interestingly, Nature has given an essential role to copper compounds in some biological systems, relying on their kinetic lability and versatile coordination environment. Some basic properties of Cu(I) and Cu(II) such as their coordination geometries and electronic levels are compared, pointing out the limited significance of Cu(II) compounds (d 9 configuration) in terms of photophysical properties. Well-established synthetic protocols are available to build up a variety of molecular and supramolecular architectures (e.g. catenanes, rotaxanes, knots, helices, dendrimers, cages, grids, racks, etc.) containing Cu(I)-based centers and exhibiting photo- and electroluminescence as well as light-induced intercomponent processes. By far the largest class of copper complexes investigated to date is that of Cu(I)-bisphenanthrolines ([Cu(NN)2]+) and recent progress in the rationalization of their metal-to-ligand charge-transfer (MLCT) absorption and luminescence properties are critically reviewed, pointing out the criteria by which it is now possible to successfully design highly emissive [Cu(NN)2]+ compounds, a rather elusive goal for a long time. To this end the development of spectroscopic techniques such as light-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS) and femtosecond transient absorption have been rather fruitful since they have allowed us to firmly ground the indirect proofs of the molecular rearrangements following light absorption that had accumulated in the past 20 years. A substantial breakthrough towards highly emissive Cu(I) coordination compounds is constituted by heteroleptic Cu(I) complexes containing both N- and P-coordinating ligands ([Cu(NN)(PP)]+) which may exhibit luminescence quantum yields close to 30% in deaerated CH2Cl2 solution and have been successfully employed as active materials in OLED and LEC optoelectronic devices. Also copper clusters may exhibit luminescence bands of halide-to-metal charge transfer (XMCT) and/or cluster centered (CC) character and they are briefly reviewed along with miscellaneous Cu(I) compounds that recently appeared in the literature, which show luminescence bands ranging from the blue to the red spectral region.

Photochemistry and Photophysics of Coordination Compounds: Copper

Copper(I) halides: A versatile family in coordination chemistry and crystal engineering

Copper(I)iodide reacts with pyridine to form (Cu py)I, and further to form (Cu py2)I. A tripyridino compound, although existing in contact with pyridine, is not obtainable at room temperature and normal pressure.

The three solvates are different in structure and in their fluorescence colour in ultraviolet light.

(Cu py3)I crystals are not fluorescent at room temperature but show yellow fluorescence at −180°C. (Cu py2)I is fluorescent with a green colour at room temperature as well as at very low temperatures. (Cu py)I shows yellow fluorescence at room temperature which reversibly changes to orange, then to red and finally to violet by cooling in liquid nitrogen („fluorescence thermochromism”). The last named compound is spontaneously decomposed by benzene to form highly dispersed copper iodide, which fluoresces red at room temperature, but not at all in liquid nitrogen.

A. Pierre

Papers

Fluorescence thermochromism of pyridine copper iodides and copper iodide