SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF POLYMER-BOUND HEXANUCLEAR MOLYBDENUM CLUSTERS

Abstract

The coordination of [Mo{sub 6}Cl{sub 8}{sup i}(SO{sub 3}CF{sub 3}){sub 6}{sup a}]{sup 2-} (1) and [Mo{sub 6}Cl{sub 8}{sup I}Cl{sub 4}{sup a}(EtOH){sup a}{sub 2}] (2) to poly(e-vinylpyridine) (PVP) produces crosslinked materials. Formation of these materials occurs by displacement of axial ligands SO{sub 3}CF{sub 3}{sup -} or EtOH on the clusters by the vinylpyridine moieties. The availability of six coordination sites in 1 and two coordination sites in 2 offers control over the degree of crosslinking and solubility of the materials. Similarly, varying the ratio of cluster coordination sites (C) to polymer-pendent pyridine ligands (P) yields materials with a wide range of solubilities and glass transition temperatures (T{sub g}). Materials with C:P ratios of 1:100 are highly soluble in CH{sub 2}Cl{sub 2} and MeOH, with T{sub g} are obtained with C:P ratios of 1:5 and lower, indicating a high degree of crosslinks. Transient emission spectroscopy reveals that polymer-bound cluster 1 lacks the luminescent properties characteristic of many [Mo{sub 6}Cl{sub 8}]{sup 4+} based clusters. Conversely, polymer-bound cluster 2 displays intense luminescence and retains the unusually long-lived excited-state observed for the free clusters in solution. The emission lifetime of PVP-bound 2 fits a biexponential decay, with {tau}{sub 1} = 90 {mu}s (60%) and {tau}{sub 2}more » = 8 {mu}s (40%), while [Mo{sub 6}Cl{sub 8}{sup i}Cl{sub 6}{sup a}]{sup 2-} has a uniexponential decay of {tau} = 156 {mu}s in CH{sub 2}Cl{sub 2} solution.« less