Robert J. Crutchley

Photosensitized singlet oxygen and its applications

The study of singlet molecular oxygen production and reactivity has emerged as a rich and diverse area with implications in fields ranging from polymer science to cancer therapy. In this review, we address the photophysical properties of singlet oxygen and of the photosensitizers used in its generation. Photosensitizers based on organic molecules and coordination compounds are examined and compared. Recent advances in the photosensitized production of singlet oxygen and its uses in photochemistry and photobiology are highlighted, with particular focus on its role in wastewater treatment, fine chemical synthesis, and photodynamic therapy (PDT). Future directions in photosensitizer development and singlet oxygen applications are also explored. # 2002 Elsevier Science B.V. All rights reserved.

Intervalence Charge Transfer and Electron Exchange Studies of Dinuclear Ruthenium Complexes

Publisher Summary This chapter discusses the theory of mixed-valence systems and theory of electron exchange. In the case of strong coupling, for which it is no longer appropriate to use perturbation theory, the interaction of states is so great that bonding and antibonding potential energy curves result. Because the ground state is delocalized between metal ions, it is not strictly appropriate to describe the intervalence transition band of a class III complex as a metal-to-metal charge transfer transition. The metal-to-metal charge transfer (MMCT) designation is used for the sake of simplicity. The dependence of intervalence transition energy on the activation barrier to thermal electron transfer allows the solvent dependence of intervalence transitions to be understood in terms of relationships developed for the Marcus Theory of electron transfer. The Hush model is the preferred method of analysis of mixed valence complexes for the experimentalist because of its readily understandable derivation, its overlap with the Marcus theory of electron transfer, and the facility of its application. However, it is applicable only to weakly coupled class II complexes. A quantitative theory that is applicable to all mixed valence complexes is desirable.

Modulation of electronic couplings within Ru2-polyyne frameworks.

Dimers of [Ru(2)(Xap)(4)] bridged by 1,3,5-hexatriyn-diyl (Xap are 2-anilinopyridinate and its aniline substituted derivatives), [Ru(2)(Xap)(4)](2)(μ-C(6)) (1), were prepared. Compounds 1 reacted with 1 equiv of tetracyanoethene (TCNE) to yield the cyclo-addition/insertion products [Ru(2)(Xap)(4)](2){μ-C≡CC(C(CN)(2))-C(C(CN)(2))C≡C} (2) and 1 equiv of Co(2)(dppm)(CO)(6) to yield the η(2)-Co(2) adducts to the middle C≡C bond, [Ru(2)(Xap)(4)](2)(μ-C(6))(Co(2)(dppm)(CO)(4)) (3). Voltammetric and spectroelectrochemical studies revealed that (i) two Ru(2) termini in 1 are sufficiently coupled with the monoanion (1(-)) as a Robin-Day class II/III mixed valence species; (ii) the coupling between two Ru(2) is still significant but somewhat weakened in 3; and (iii) the coupling between two Ru(2) is completely removed by the insertion of TCNE in 2. The attenuation of electronic couplings in 2 and 3 was further explored with both the X-ray diffraction study of representative compounds and spin-unrestricted DFT calculations.

Phenylcyanamide ligands and their metal complexes

Abstract This review examines the various synthetic routes to phenylcyanamide ligands, and their physical characterization by electronic, NMR and IR spectroscopies, crystallography and theoretical methods. While the coordination chemistry of phenylcyanamide ligands is largely unexplored, a significant number of mononuclear coordination complexes of ruthenium, copper and nickel group ions have been synthesized. Topics to be covered are UV–vis, NMR and IR spectroscopy, linkage isomerism and crystallography, and finally cyclic voltammetry. Studies of the remarkable ability of the 1,4-dicyanamidobenzene dianion bridging ligand to mediate antiferromagnetic or resonance exchange in dinuclear ruthenium complexes will be reviewed.

Diruthenium–Polyyn-diyl–Diruthenium Wires: Electronic Coupling in the Long Distance Regime

Reported herein is a series of Ru2(Xap)4 capped polyyn-diyl compounds, where Xap is either 2-anilinopyridinate (ap) or its aniline substituted derivatives. Symmetric [Ru2(Xap)4](μ-C4k)[Ru2(Xap)4] (compounds 4ka (X = 3-isobutoxy) and 4kc (X = 3,5-dimethoxy) with k = 2, 3, 4, and 5) was obtained from the Glaser coupling reaction of Ru2(Xap)4(C2kH). Unsymmetric [Ru2(Xap)4](μ-C(4k+2))[Ru2(ap)4] (compounds 4k+2b with k = 2, 3, and 4) were prepared from the Glaser coupling reaction between Ru2(Xap)4(C(2k+2)H) and Ru2(ap)4(C2kH). X-ray diffraction study of compound 12c revealed both the sigmoidal topology of the polyyn-diyl bridge and the fine structural detail about the Ru2 cores. Cyclic and differential pulse voltammetric (CV and DPV) measurements and spectroelectrochemical studies revealed that (i) the reduced monoanions [Ru2-C2m-Ru2](-1) (m = 4-8) belong to the Robin-Day class II mixed valent ions and (ii) the electronic coupling between Ru2 termini depends on the length of the polyyn-diyl bridge with an attenuation constant (γ) between 0.12 and 0.15 Å(-1). In addition, spin-unrestricted DFT calculations provide insight about the nature of orbitals that mediate the long distance electronic coupling.

(1,3-Bis(2′-pyridylimino)isoindolinato)nickel(II) complexes of phenylcyanamido ligands: crystal structure, electronic absorption spectroscopy and solvent adduct studies

Abstract Complexes of the formula Ni(L)X, where L=1,3-bis(2′-pyridylimino)isoindolinato and X=Cl, Br, N3, NCS, 2-Clpcyd, 4-Clpcyd, 2,3-Cl2pcyd,2,6-Cl2pcyd, 2,4,5-Cl3pcyd and 2,3,5,6-Cl4pcyd, have been synthesized and characterized by elemental analysis, and IR, 1H NMR and UVVis spectroscopies. A crystal structure determination of Ni(L)(2-Clpcyd) showed nickel in a distorted square planar coordination sphere of nitrogen donor atoms in which the phenylcyanamido ligand is coordinated to Ni(II) via the terminal nitrogen. The solvent coordination equilibria of Ni(L)(pcyd) complexes was also investigated and the results suggest that both electronic and steric factors play important roles in determining the stability of the solvated complex.

Water-Based Oxygen-Sensor Films

The luminescent cyclometalated iridium complex [Ir(fppy)(2)(t-Bu-iCN)(2)]CF(3)SO(3), 1 (fppy = 4-(2-pyridyl)benzaldehyde, and t-Bu-iCN = tert-butyl isocyanide), was synthesized and characterized by X-ray crystallography and (1)H NMR, absorption, and emission spectroscopies. Complex 1 was quantitatively bound to the water-soluble amine-functionalized polymer Silamine D208-EDA by reductive amination, to produce 2. The quantum yield of emission and excited state lifetime of 2 (varphi(em) = 0.23 and tau = 20.6 mus) are comparable to that of the model complex [Ir(tpy)(2)(t-Bu-iCN)(2)]CF(3)SO(3), 3 (tpy = 2-(p- tolyl) pyridine) with varphi(em) = 0.28 and tau = 35.6 mus. Aqueous blends of 2 with Silamine and colloidal microcrystalline cellulose (MC) were used to prepare oxygen-sensor films. Oxygen sensitivities of these films were determined as a function of Silamine:MC ratio and obeyed Stern-Volmer kinetics. The optimum oxygen-sensor film composition was 2 in 1:1 Silamine:MC, which had an oxygen sensitivity of 0.502 over an atmospheric pressure range of 0.007-45 psi. Temperature sensitivity (percentage loss of intensity per degrees C) of this film was determined to be -1.1 and -1.4% degrees C(-1) at vacuum and 1 bar atmospheric pressure, respectively. These results were compared to those of films incorporating dispersions of 1 and 3. Luminescence microscopy of 9:1, 1:1, and 1:5 Silamine:MC films of 2 show that the charged iridium complex in 2 associates with the surface of MC and lifetime measurements of these films show an increase in lifetime with increasing MC fraction. The optimum quenching sensitivity observed for the 1:1 Silamine:MC film suggests that the diffusion of oxygen must decrease with increasing fraction of MC and thereby decrease oxygen sensitivity. These novel materials offer an environmentally friendly alternative to the preparation of oxygen-sensor films.

Solvent trapped valency in the [bis(pentaammineruthenium)-(μ-1,4-dicyanamidobenzene)] trication

Abstract Cyclic voltammetry measurements show an unprecedented solvent dependence of metal-metal coupling for the symmetric mixed valence [3,2] complex, [{(NH3)5Ru}2(μ-dicyd)]3+, where dicyd2− is the 1,4-dicyanamidobenzene dianion. The comproportionation constant was determined to be Kc=10 and 68 400 in aqueous and acetonitrile solution, respectively. The intervalence absorption band was deconvoluted from the low energy Ru(III)-cyanamide LMCT band by curve fitting analysis which gave for the [3,2] complex assuming a gaussian IT band, Eop=8190 cm−1, Δ ν 1 2 =4090 cm−1 and ϵmax=2590 M−1 cm−1 in aqueous solution and in acetonitrile solution Eop=6910 cm−1, Δ ν 1 2 =2640 cm−1 and ϵmax=19 400 M−1 cm−1. It is suggested that donor-acceptor interactions between the solvent and ammine protons weakens the Ru(III)-cyanamide π bond. Because the interaction between Ru(III) and the cyanamide group is crucial to superexchange, metal-metal coupling is also weakened. The acceptor properties of water may also play a role.

Fc-Fc Electronic Interaction through Equatorial Pathways of a Diruthenium Core

Diruthenium compounds bearing one (3) and two (4) ferrocene carboxylate ligands were prepared and characterized, and the electronic coupling between two equatorially adjacent Fc centers in compound 4 is significant, but weaker than those between Fc centers placed on the opposite axial sites.

The Dependence of Ligand to Metal Charge Transfer Oscillator Strength on the Nature of the Ruthenium (III)-Cyanamide Bond: Outersphere Perturbations

Abstract The extent of electronic coupling between donor and acceptor wave-functions can play a dominant role in determining the rate of electron transfer. This is particularly true for biological electron transfer systems in which the redox sites are far apart or linked by a bridging ligand. In this study, we have investigated the extent to which electronic coupling between Ru(III) and an an — ionic phenylcyanamide ligand as measured by the b1* ← b1 LMCT oscillator strength is affected by the nature of the outer coordination sphere. The LMCT oscillator strength was found to decrease with increasing solvent donor number. We suggest that the trend in oscillator strength can largely be rationalized in terms of the magnitude of the π overlap between Ru(III) and cyanamide anion group. When the cyanamide anion group is incorporated into the bridging ligand of a Ru(III, II) mixed—valence complex, the oscillator strength of the resulting LMCT band will be a probe of the extent to which the acceptor wavefunction ...