Spatial extensions of excited states of metal complexes. Tunability by chemical variation

The ligand-ligand coupling in excited states of homoleptic metal-organic an d related compounds of the platinum metal group depends strongly on the met al d or MLCT character in these states. In particular, in triplet slates, w hich mostly represent the lowest excited states, the metal participation is displayed in the amount of zero-field splitting (zfs) Detailed investigati ons in recent years have demonstrated that complexes with very small metal participation and thus small zfs, like [Rh(bpy)(3)](3+) and [Pt(bpy)(3)](3), exhibit spatially localized or ligand-centered triplets. Compounds with large metal character as in (MLCT)-M-3 states have large zfs, and the state s are delocalized over the metal and the different ligands, as found for [R U(bpy)(3)](2+) and [Os(bpy)(3)](2+). By chemical variation, it is possible to obtain a compound characterized by an intermediate position between the two extreme situations. Such a compound is Pt(2-tbpy)(2) with 2-thpy(-) = 2 -(2-thienylpyridinate). It is one of the main subjects of this investigatio n to study whether in Pt(2-thpy)(2) the lowest excited triplet is spatially extended over both ligands. This is done by comparing highly resolved emis sion (and excitation) spectra of perprotonated Pt(2-thpy-h(6))(2), partiall y deuterated Pt(2-thpy-h(6))(2-thpy-d(6)), and perdeuterated Pt(2-thpy-d(6) )(2). These spectra display clear fingearprints with respect to spatial ext ensions of the excited states. The required high resolution is obtained whe n the compounds are dissolved in an n-octane matrix (Shpol'skii matrix) and are measured at low temperature (T = 1.3 and 4.2 K). The deuterated compou nds are studied for the first time. Interestingly, it is found that all thr ee triplet sublevels of Pt(2-thpy)(2) are spatially extended over both liga nds. This result is of high importance, since it tells us that already a mo derate metal d or MLCT character in the lowest triplet stare of homoleptic compounds of the platinum metal group leads, at least in a rigid matrix, to spatially delocalized excited states.