Structural and spectroscopic studies of three-coordinate copper(I) supported by bis(phosphino)borate ligands

Photophysical characteristics and reactivity of bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I)

The recently synthesized sterically constrained copper(I) complex [Cu(dtbp)(2)](+) (1), where dtbp is 2,9-di-tert-butyl-1,10-phenanthroline, exhibits unique photophysical and reactivity properties. Complex 1 (lambda(abs), 425 nm; epsilon, 3100 L M(-1) cm(-1); lambda(emission), 599 nm) has the longest metal-to-ligand charge-transfer (MLCT) emission lifetime (tau, 3260 ns) and largest quantum yield (varphi, 5.6%) of all [Cu(R(2)phen)(2)](+) complexes. Complex 1 also exhibits a large positive reduction potential for the [Cu(2+)(dtbp)(2)]|[Cu(+)(dtbp)(2)] couple (E(1/2) = 0.70 V vs Fc(+/0)) and a large negative excited-state reduction potential for the [Cu(2+)(dtbp)(dtbp(-*))]|[Cu(2+)(dtbp)(2)] couple (E(1/2) = -1.66 V vs Fc(+/0)), indicating that this complex is a potent photoreductant in the excited state. The steric constraint imposed by the t-butyl substituents in 1 enables unusual ligand replacement reactivity. Either CH(3)CN or CO replaces one of the dtbp ligands, a reaction that is readily followed by loss of the unique emission signature of 1. Monodentate CH(3)CN binds to the copper(I) center with an affinity 2 orders of magnitude greater than that of the displaced dtbp, despite the fact that the displaced ligand is bidentate. CO-induced displacement of dtbp from 1 is reversible, but only in the presence of 1 equiv of unbound dtbp. The exceptionally strong donor ligand CH(3)NC displaces both dtbp ligands from 1. In contrast to the facile ligand displacement reactivity with good donor ligands, 1 does not react readily with O(2), by either a ligand displacement or an oxidative pathway. Rather, O(2) induces partial quenching of emission via an outer-sphere interaction with 1.

Phosphorescent Cu(I) Complexes of 2-(2‘-pyridylbenzimidazolyl)benzene: Impact of Phosphine Ancillary Ligands on Electronic and Photophysical Properties of the Cu(I) Complexes

Four mononuclear Cu(I) complexes of 2-(2'-pyridyl)benzimidazolylbenzene (pbb) with four different ancillary phosphine ligands PPh(3), bis[2-(diphenylphosphino)phenyl]ether (DPEphos), bis(diphenylphosphino)ethane (dppe), and bis(diphenylphosphinomethyl)diphenylborate (DPPMB) have been synthesized. The crystal structures of [Cu(pbb)(PPh(3))(2)][BF(4)] (1), [Cu(pbb)(dppe)][BF(4)] (2), [Cu(pbb)(DPEphos)][BF(4)] (3), and the neutral complex [Cu(pbb)(DPPMB)] (4) were determined by single-crystal X-ray diffraction analyses. The impact of the phosphine ligands on the structures of the copper(I) complexes was examined, revealing that the most significant impact of the phosphine ligands is on the P-Cu-P bond angle. The electronic and photophysical properties of the new complexes were examined by using UV-vis, fluorescence, and phosphorescence spectroscopies and electrochemical analysis. All four complexes display a weak MLCT absorption band that varies considerably with the phosphine ligand. At ambient temperature, no emission was observed for any of the complexes in solution. However, when doped into PMMA polymer (20 wt %), at ambient temperature, all four complexes emit light with a color ranging from green to red-orange, depending on the phosphine ligand. The emission of the new copper complexes has an exceptionally long decay lifetime (>200 micros). Ab initio MO calculations established that the lowest electronic transition in the copper(I) complexes is MLCT in nature. The electronic and photophysical properties of the new mononuclear Cu(I) complexes were compared with those of the corresponding polynuclear Cu(I) complexes based on the 2-(2'-dipyridyl)benzimidazolyl derivative ligands and the previously extensively studied phenanthroline-based Cu(I) complexes.