Published: October 21, 2011 r2011 American Chemical Society 11309 dx.doi.org/10.1021/ic2006343 | Inorg. Chem. 2011, 50, 11309–11322 ARTICLE pubs.acs.org/IC New Heteroleptic Bis-Phenanthroline Copper(I) Complexes with Dipyridophenazine or Imidazole Fused Phenanthroline Ligands: Spectral, Electrochemical, and Quantum Chemical Studies Yann Pellegrin, † Martina Sandroni, † Errol Blart, † Aur  elien Planchat, † Michel Evain,* ,§ Narayan C. Bera, ‡ Megumi Kayanuma, ‡ Michel Sliwa,* ,|| Mateusz Rebarz, || Olivier Poizat, || Chantal Daniel,* ,‡ and Fabrice Odobel* ,† † CEISAM, Universit  e de Nantes, CNRS, 2 rue de la Houssini  ere, 44322 Nantes Cedex 3, France ‡ Laboratoire de Chimie Quantique, Institut de Chimie, UMR 7177 CNRS-Universit  e de Strasbourg, 4 rue Blaise Pascal, CS 90032, F-67081 Strasbourg Cedex, France § IMN, Universit  e de Nantes, CNRS, 2 rue de la Houssini  ere, 44322 Nantes Cedex 3, France ) Laboratoire de Spectrochimie Infrarouge et Raman, UMR 8516 CNRS-Universit  e Lille 1 Sciences et Technologies, 59655 Villeneuve d’Ascq Cedex, France b S Supporting Information ’ INTRODUCTION Copper(I)diimine complexes ([Cu I (diimine) 2 ] + ), where the diimine ligand is α-substituted by bulky groups, have attracted much attention since the discovery of their lumines- cence properties in solution and in the solid state. 15 They share with rutheniumpolypyridine complexes several appealing fea- tures for solar energy conversion, in particular the existence of a metal to ligand charge transfer transition (MLCT) around 460 nm, which could be formally described as [Cu II (imine • )- (imine)] + . 36 Importantly, the presence of sterically challenging groups in the α position of the coordinating nitrogen atoms is mandatory to observe photoluminescence, since they prevent the flattening distortion of the complex from the Cu I preferred tetrahedral geometry to the formal Cu II square planar arrange- ment, leading to a very efficient quenching of the excited state. However, the rather low molar extinction coefficient of the MLCT absorption band and the ligand scrambling around Cu(I), pre- venting the isolation of a stable [Cu I (imine A )(imine B )] + hetero- leptic complex, has put a dramatic curb on the development of Received: March 28, 2011 ABSTRACT: Two new sterically challenged diimine ligands L 1 (2,9-dimesityl- 2-(4 0 -bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L 2 (3,6-di- n- butyl-11-bromodipyrido[3,2-a:2 0 ,3 0 -c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L 1 is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L 2 is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L 1 , L 2 , and complementary matching ligands (2,9-R 2 -1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L 2 , bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L 1 . For example, a luminescence quantum yield of about 3  10 4 is obtained with a decay time of about 50 ns for C2 ([Cu I (nBu-phen)(L 1 )] + ) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu I (Mes-phen)(L 2 )] + ). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L 1 and L 2 are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)phenanthroline complexes.