Nature of Excited States of Ruthenium-Based Solar Cell Dyes in Solution: A Comprehensive Spectroscopic Study.

The photophysical properties of a number of ruthenium complexes of the general structure [Ru(L1)(L2)(NCS)2], related to the prominent solar cell dye [Ru(dcb)2(NCS)2] (dcb = 4,4'-dicarboxylato-2,2'-bipyridine) are investigated. For L1 = dcb and dmb (dmb = 4,4'-dimethyl-2,2'-bipyridine), several variations of L2 show very little difference in the lowest energy absorption peak. Resonance Raman and density functional theory calculations have been used to assign the corresponding transitions as {Ru(NCS)2} → dcb with significant contributions of the NCS ligands. Transient absorption, time-resolved infrared, and transient resonance Raman spectroscopic techniques were used to probe the photophysics of the complexes and relatively short-lived {Ru(NCS)2} → dcb/dpb (dpb = 4,4'-diphenylethenyl-2,2'-bipyridine) excited states were observed with the exception of [Ru(dcb)(dab)(NCS)2] (dab = 4,4'-dianthracenethenyl-2,2'-bipyridine), which showed a long-lived excited state assigned as ligand centered charge separated.

Re(I) complexes of substituted dppz: a computational and spectroscopic study.

A series of dipyrido[3,2-a:2',3'-c]phenazine (dppz)-based ligands with electron-withdrawing substituents and their [Re(CO)3(L)Cl] and [Re(CO)3(L)(py)]PF6 complexes have been studied using Raman, resonance Raman, and transient resonance Raman (TR(2)) and time-resolved infrared (TRIR) spectroscopic techinques in conjunction with computational chemistry as well as electrochemical studies, emission, and absorption of ground and excited states. DFT (B3LYP) frequency calculations show good agreement with nonresonant Raman spectra, which allowed these to be used to identify phenanthroline, phenazine, and delocalized modes. These band assignments were used to establish the nature of chromophores active in resonance Raman spectra, probed with wavelengths between 350.7 and 457.9 nm. X-ray crystallography of [Re(CO)3(dppzBr2)Cl] and [Re(CO)3(dppzBr)(py)]PF6 showed these crystallize in space groups triclinic P1 and monoclinic P2(1/n), respectively. Electrochemical studies showed that substituents have a strong effect on the phenazine MO, changing the reduction potential by 200 mV. Transient absorption studies showed that generally the [Re(CO)3(L)(py)]PF6 complexes had longer lifetimes than the corresponding [Re(CO)3(L)Cl] complexes; the probed state is likely to be (3)π → π* (phz) in nature. TR(2) spectra of the ligands provided a marker for the triplet π → π* state, and the TR(2) spectra of the complexes suggest an intraligand (IL) π,π* state for [Re(CO)3(L)(py)](+) complexes, and a potentially mixed IL/MLCT state for [Re(CO)3(L)Cl] complexes. TRIR spectroscopy is more definitive with THEXI state assignments, and analysis of the metal-carbonyl region (1800-2100 cm(-1)) on the picosecond and nanosecond time scales indicates the formation of MLCT(phen/phz) states for all [Re(CO)3(L)Cl] complexes, and IL π → π* (phen) states for all [Re(CO)3(L)(py)](+) complexes, with all but [Re(CO)3(dppzBr(CF3))(py)](+) showing some contribution from an MLCT(phen) state also.

Intraligand charge-transfer excited states in Re(I) complexes with donor-substituted dipyridophenazine ligands.

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.

Dual charge-transfer in rhenium(I) thioether substituted hexaazanaphthalene complexes.

The ligand 2,3,8,9,14,15-hexa(octyl-thioether)-5,6,11,12,17,18-hexaazatrinaphthalene (HATN-(SOct)6) and its mono-, bi-, and trinuclear Re(CO)3Cl complexes are reported. These are characterized by (1)H NMR spectroscopy and electrochemistry, and show broad, intense absorption across the visible wavelength region. Using time-dependent density functional theory (TD-DFT) calculations and resonance Raman spectroscopy these absorption bands are shown to be π → π*, MLCT, ILCT(sulfur → HATN), or mixed MLCT/ILCT in nature. Time-resolved infrared spectroscopy is used to probe structural changes and dynamics on short time scales and supports the assignment of a mixed MLCT/ILCT state in which both sulfur groups and one metal center act as electron donors to the HATN core.

Heteroleptic Cu(I) bis-diimine complexes of 6,6'-dimesityl-2,2'-bipyridine: a structural, theoretical and spectroscopic study.

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.

Synthesis, characterization, and photophysics of oxadiazole- and diphenylaniline-substituted Re(I) and Cu(I) complexes.

Transition-metal complexes of the types [Re(CO)(3)Cl(NN)], [Re(CO)(3)py(NN)](+), and [Cu(PPh(3))(2)(NN)](+), where NN = 4,4'-bis(5-phenyl-1,3,4-oxadiazol-2-yl)-2,2'-bipyridine (OX) and 4,4'-bis(N,N-diphenyl-4-[ethen-1-yl]-aniline)-2,2'-bipyridine (DPA), have been synthesized and characterized. Crystal structures for [Re(CO)(3)Cl(DPA)] and [Cu(PPh(3))(2)(OX)]BF(4) are presented. The crystal structure of the rhenium complex shows a trans arrangement of the ethylene groups, in agreement with density functional theory calculations. The structure of the copper complex displays the planar aromatic nature of the bpy-oxadiazole ligand. Density functional theory modeling of the complexes was supported by comparison of calculated and experimental normalized Raman spectra; the mean absolute deviations of the complexes were <10 cm(-1). The Franck-Condon state was investigated using UV-vis and resonance Raman spectroscopic as well as density functional theory computational techniques. It was shown that the lowest energy absorption peaks are metal to ligand charge transfer and ligand-centered charge transfer for the oxadiazole- and diphenylaniline-substituted bipyridine ligands, respectively. The lowest energy excited states were characterized using transient emission and absorption spectroscopic techniques in conjunction with density functional theory calculations. These showed that the DPA complexes had ligand-centered nonemissive "dark" states with lifetimes ranging from 300 to 2000 ns.

Complete family of mono-, bi-, and trinuclear Re(I)(CO)3Cl complexes of the bridging polypyridyl ligand 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinapthalene: syn/anti isomer separation, characterization, and photophysics.

The syn and anti isomers of the bi- and trinuclear Re(CO)(3)Cl complexes of 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinapthalene (HATN-Me(6)) are reported. The isomers are characterized by (1)H NMR spectroscopy and X-ray crystallography. The formation of the binuclear complex from the reaction of HATN-Me(6) with 2 equiv of Re(CO)(5)Cl in chloroform results in a 1:1 ratio of the syn and anti isomers. However, synthesis of the trinuclear complex from the reaction of HATN-Me(6) with 3 equiv of Re(CO)(5)Cl in chloroform produces only the anti isomer. syn-{(Re(CO)(3)Cl)(3)(µ-HATN-Me(6))} can be synthesized by reacting 1 equiv of Re(CO)(5)Cl with syn-{(Re(CO)(3)Cl)(2)(µ-HATN-Me(6))} in refluxing toluene. The product is isolated by subsequent chromatography. The X-ray crystal structures of syn-{(Re(CO)(3)Cl)(2)(µ-HATN-Me(6))} and anti-{(Re(CO)(3)Cl)(3)(µ-HATN-Me(6))} are presented both showing severe distortions of the HATN ligand unit and intermolecular π stacking. The complexes show intense absorptions in the visible region, comprising strong π → π* and metal-to-ligand charge-transfer (MLCT) transitions, which are modeled using time-dependent density functional theory (TD-DFT). The energy of the MLCT absorption decreases from mono- to bi- to trinuclear complexes. The first reduction potentials of the complexes become more positive upon binding of subsequent Re(CO)(3)Cl fragments, consistent with changes in the energy of the MLCT bands and lowering of the energy of relevant lowest unoccupied molecular orbitals, and this is supported by TD-DFT. The nature of the excited states of all of the complexes is also studied using both resonance Raman and picosecond time-resolved IR spectroscopy, where it is shown that MLCT excitation results in the oxidation of one rhenium center. The patterns of the shifts in the carbonyl bands upon excitation reveal that the MLCT state is localized on one rhenium center on the IR time scale.

Discovery of AL-GDa62 as a Potential Synthetic Lethal Lead for the Treatment of Gastric Cancer.

Diffuse gastric cancer and lobular breast cancer are aggressive malignancies that are frequently associated with inactivating mutations in the tumor suppressor gene CDH1. Synthetic lethal (SL) vulnerabilities arising from CDH1 dysfunction represent attractive targets for drug development. Recently, SLEC-11 (1) emerged as a SL lead in E-cadherin-deficient cells. Here, we describe our efforts to optimize 1. Overall, 63 analogues were synthesized and tested for their SL activity toward isogenic mammary epithelial CDH1-deficient cells (MCF10A-CDH1-/-). Among the 26 compounds with greater cytotoxicity, AL-GDa62 (3) was four-times more potent and more selective than 1 with an EC50 ratio of 1.6. Furthermore, 3 preferentially induced apoptosis in CDH1-/- cells, and Cdh1-/- mammary and gastric organoids were significantly more sensitive to 3 at low micromolar concentrations. Thermal proteome profiling of treated MCF10A-CDH1-/- cell protein lysates revealed that 3 specifically inhibits TCOF1, ARPC5, and UBC9. In vitro, 3 inhibited SUMOylation at low micromolar concentrations.

Effect of sulfur-based substituents on the electronic properties of Re(I) dppz complexes.

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.

Stretching the phenazine MO in dppz: the effect of phenyl and phenyl-ethynyl groups on the photophysics of Re(I) dppz complexes.

A series of dipyrido[3,2-a:2',3'-c]phenazine (dppz)-based ligands have been synthesised in which phenyl or phenyl-ethynyl linkers are terminated by (t)Bu or CN units. The corresponding [ReCl(CO)3(L)] complexes are also prepared. Electrochemistry shows the ligand which contains a phenyl-ethynyl linker and CN substituent is most easily reduced (by 15 mV relative to the other ligands). All complexes are reduced and oxidised at similar potentials. Electronic absorption spectra are consistent with stabilisation of the LUMO by the binding of the metal centre, as complex spectra are red-shifted relative to their ligand. In addition, those containing phenyl-ethynyl linkers show spectra red-shifted (by 650 cm(-1)) relative to their phenyl-linked analogues. Raman and resonance Raman spectroscopy combined with DFT and TD-DFT calculations are consistent with ligands showing π,π* transitions, and complexes showing metal-to-ligand charge-transfer (MLCT) transitions as the lowest energy absorption. Ligands emit from the π,π* excited state (λem ranging from 450 to 470 nm in CH2Cl2). The complexes show emission from both π,π* and MLCT states; the λem(MLCT) lies at 650-666 nm. Transient lifetimes in CH2Cl2 are decreased by the CN substituent, as this increases knr. Transient resonance Raman spectra (TR(2)) of ligands show spectral features associated with the LC state, and the strong similarities between these and complex spectra support an LC excited state at 355 nm for the complexes. Two-colour TR(3) spectra show only small differences to ground state spectra, the most obvious being a decrease in intensity of C[triple bond, length as m-dash]C bands. For [ReCl(CO)3()] and [ReCl(CO)3()] an increase in intensity of a 1575 cm(-1) band attributed to the dppz˙(-) species suggests that these complexes have significant MLCT state population between 20-60 ns after photoexcitation.