The donor-acceptor ligands 11-(4-diphenylaminophenyl)dipyrido[3,2-a:2',3'-c]phenazine (dppz-PhNPh2) and 11-(4-dimethylaminophenyl)dipyrido[3,2-a:2',3'-c]phenazine (dppz-PhNMe2), and their rhenium complexes, [Re(CO)3X] (X = Cl(-), py, 4-dimethylaminopyridine (dmap)), are reported. Crystal structures of the two ligands were obtained. The optical properties of the ligands and complexes are dominated by intraligand charge transfer (ILCT) transitions from the amine to the dppz moieties with λabs = 463 nm (ε = 13 100 M(-1) cm(-1)) for dppz-PhNMe2 and with λabs = 457 nm (ε = 16 900 M(-1) cm(-1)) for dppz-PhNPh2. This assignment is supported by CAM-B3LYP TD-DFT calculations. These ligands are strongly emissive in organic solvents and, consistent with the ILCT character, show strong solvatochromic behavior. Lippert-Mataga plots of the data are linear and yield Δμ values of 22 D for dppz-PhNPh2 and 20 D for dppz-PhNMe2. The rhenium(I) complexes are less emissive, and it is possible to measure resonance Raman spectra. These data show relative band intensities that are virtually unchanged from λexc = 351 to 532 nm, consistent with a single dominant transition in the visible region. Resonance Raman excitation profiles are solvent sensitive; these data are modeled using wavepacket theory yielding reorganization energies ranging from 1800 cm(-1) in toluene to 6900 cm(-1) in CH3CN. The excited state electronic absorption and infrared spectroscopy reveal the presence of dark excited states with nanosecond to microsecond lifetimes that are sensitive to the ancillary ligand on the rhenium. These dark states were assigned as phenazine-based (3)ILCT states by time-resolved infrared spectroscopy. Time-resolved infrared spectroscopy shows transient features in which Δν(CO) is approximately -7 cm(-1), consistent with a ligand-centered excited state. Evidence for two such states is seen in mid-infrared transient spectra.

A series of sulfur-substituted dppz-based ligands and their Re(I)(CO)(3)Cl complexes are reported. The sulfur-substituted ligands and complexes show interesting electronic properties atypical of dppz-type systems. Substitution of dppz with thiocyanate (SCN) groups results in behavior typical of an electron withdrawing group. However, substitution of dppz with the electron donating trithiocarbonate (S(2)CS) or deca-alkylthioether (Sdec) groups confer intraligand charge-transfer (ICT) from the S adduct to the phenazine lowest unoccupied molecular orbital (LUMO). Upon complexation of the substituted dppz ligand to Re(CO)(3)Cl this ICT red-shifts and increases in intensity. Analysis of these observations using density functional theory (DFT) calculations and resonance Raman spectroscopy reveals that these transitions are a mixture of metal-to-ligand charge-transfer (MLCT) and S --> phenazine ICT in nature. The synthesized compounds are also characterized using (1)H NMR spectroscopy, IR spectroscopy, and electrochemistry. Single-crystal X-ray analysis was performed on dppz(SCN)(2) (C(20)H(18)N(6)S(2) a = 8.780 A, b = 9.792 A, c = 10.400 A, alpha = 95.95 degrees , beta = 112.13 degrees , gamma = 95.38 degrees , triclinic, P1, Z = 2, R1 = 0.0306, wR2 = 0.0829.

A series of heteroleptic Cu(I) complexes containing 6,6'-dimesityl-2,2'-bipyridine and phenanthroline-, bipyridine-, and biquinoline-based ligands is studied. The HETPHEN strategy is utilized to synthesize the heteroleptic complexes, which are stable in solution. The X-ray crystal structures of the complexes are presented; the solid-state four-coordinate Cu(I) geometries are quantified by using the τ4 parameter. A feature of the crystal structures is the intramolecular π-stacking between the mesityl ring(s) and the diimine ligand; the phen-based complexes exhibit stacking between the phen ligand and one of the mesityl rings, creating a "Pac-Man" motif. On the other hand, the bpy-based complexes show different types of packing interaction, with both mesityl rings "clamping down" on the bpy based ligand to give π-stacking. Cyclic voltammetry is used to examine the redox chemistry of the complexes. The most positive potentials for the oxidation process are observed for the complexes with bulky substituents ortho to the coordination nitrogens atoms, i.e., 2,9-dimethyl-1,10-phenanthroline and 6,6'-dibromo-2,2'-bipyridine. The Cu(I) MLCT transitions of the complexes are investigated by resonance Raman spectroscopy in concert with TD-DFT calculations. The resonance Raman spectra of complexes containing substituted biquinolines are straightforward, in that vibrational bands of the biquinoline-based ligand are selectively enhanced over bpy(Mes)2 bands. This is consistent with the purple color of the complexes, due to the lower energy of the biquinoline-based LUMO compared to the bpy(Mes)2 LUMO. All the phen- and bpy-based complexes show enhancement of bpy(Mes)2 bands.