Bis(2,9-diphenyl-1,10-phenanthroline)copper(I): a copper complex with a long-lived charge-transfer excited state

Abstract

The title compound, [ C ~( d p p ) ~]+ (dpp = 2,9-diphenyl-I ,I 0-phenanthroline), exhibits long-lived emission at room temperature in solution, and, in contrast with copper(1) complexes of less bulky ligands, the emission persists in polar media; a water soluble derivative of [Cu(dpp),]+ is luminescent a t room temperature in aqueous solution and undergoes efficient redox photochemistry in the presence of electron acceptors.

Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution

“…These spectra are in agreement with those in the literature. 2,22,28 The excited state transient absorption spectra Transient absorption spectra were collected from very early times (<500 fs) through 2 ns after photoexcitation for [ 2 ] + Transient absorption spectra were measured in the spectral region of 450 -775 nm. In the acetonitrile solution, the entire transient spectrum exhibits a rise without any distinct features.…”

“…3,19,26 Despite the lack of any direct structural evidence, the exciplex formation hypothesis was supported by the correlation between accessibility of the cuprous center by the solvent and the luminescence lifetime, and was widely accepted. 3,19,[27][28][29] Recent contributions from our laboratory using laser-initiated time-resolved x-ray absorption spectroscopy (LITR-XAS) have confirmed the presence of additional coordination to the copper center by a solvent molecule (or counter ion) for photoexcited [Cu I (dmp) 2 ] + in both noncoordinating toluene 30 and strongly coordinating acetonitrile. 31 The interaction strength with the solvent molecule is much weaker in the former and stronger in the latter and is supported by the differentiation of the average copper to ligand distance in the thermally equilibrated 3 MLCT state.…”

Characterization and photocatalytic behavior of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes

“…69 The emission maxima in the solid state for the complexes containing the phenol groups, i.e., [Cuˑ(2) 2 ]PF 6 and [Cuˑ(4) 2 ]PF 6 , are blue-shifted relative to the dimethoxysubstituted Cu(I) phenanthroline complexes, i.e., [Cuˑ(1) 2 ]PF 6 and [Cuˑ(3) 2 ]PF 6 , as well as the emission maximum reported for the unsubstituted 2,9-diphenyl phenanthroline analog (675 nm). 8,67 This is most likely due to the electron-donating effect of the hydroxy group. The effect is somewhat modulated in the case of compound [Cuˑ(4) 2 ]PF 6 due to the electronreleasing ability of the added methyl groups.…”

“…8 We attribute these characteristics to the electron-donating ability of the hydroxy and methoxy groups to stabilize the excited-state orbitals. 67 The ability of phenolic moieties to undergo protonation/deprotonation is also well-known to red shift their emission relative to benzenoid species in solution.…”

“…7 Nevertheless, charge-transfer emission has been observed for bis-phenanthroline Cu(I) complexes in solutions of weakly coordinating solvents such as dichloromethane if the copper (I) metal center is sufficiently protected from Lewis base attack through the use of bulky phenanthroline ligands such as when phenyl groups are attached at the 2 and 9 positions. 8 The Cu(I) complexes in this study were all soluble in DCM, (the solvent used for the ATRA reactions); and room temperature MLCT emission spectra of all complexes were obtained as shown in Fig. 11.…”