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David R McMillin

Publications and source records attributed to David R McMillin.

9 recordsLinked to original sources
PubMed2006

Synthesis, electrochemistry and luminescence of [Pt{4'-(R)trpy}(CN)](+) (R = Ph, o-CH(3)C(6)H(4), o-ClC(6)H(4) or o-CF(3)C(6)H(4); trpy = 2,2':6',2''-terpyridine): crystal structure of [Pt{4'-(Ph)trpy}(CN)]BF(4) x CH(3)CN.

The synthesis and characterization of [Pt{4'-(R)trpy}(CN)]X (R = Ph, X = BF(4) or SbF(6); R = o-CH(3)C(6)H(4), X = SbF(6); R = o-ClC(6)H(4), X = SbF(6); or R = o-CF(3)C(6)H(4), X = SbF(6)) are described where trpy = 2,2':6',2''-terpyridine. Single crystals of [Pt{4'-(Ph)trpy}(CN)]BF(4).CH(3)CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4'-(Ph)trpy}(CN)]BF(4). An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9 degrees of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4'-(R)trpy}(CN)](+) cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E(1/2) values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4'-(Ph)trpy}(CN)](+) approximately [Pt{4'-(o-CH(3)C(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-ClC(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-CF(3)C(6)H(4))trpy}(CN)](+). All the [Pt(4'-(R)trpy}(CN)](+) cations are photoluminescent in dichloromethane. Emission by [Pt{4'-(Ph)trpy}(CN)](+) is from an excited state with largely (3)MLCT orbital parentage, but with some intraligand (3)pi-pi* character mixed-in (tau = 0.1 micros). In contrast, the other three cations display emission that appears exclusively intraligand (3)pi-pi* in origin (tau approximately 0.8 micros). Emission spectra have been recorded in a low concentration frozen DME {1 : 5 : 5 (v/v) DMF-MeOH-EtOH} glass. For the R = o-CH(3)C(6)H(4), o-ClC(6)H(4) and o-CF(3)C(6)H(4) cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4'-(Ph)trpy}(CN)](+) cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more "domed" pattern; this has been interpreted in terms of a higher percentage of intraligand (3)pi-pi* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric (3)pi-pi* and (3)MMLCT emission, respectively.

Journal Article↗
PubMed2005

One-dimensional supramolecular assemblies based on a Re2(III,III) synthon and their solid-state phosphorescence.

Reactions between Re2(DMBA)4(NO3)2 (1; DMBA is dimethylbenzamidinate) and a bidentate dianion, either tungstate (WO4(2-)) or terephthalte (1,4-(O2C)2C6H4(2-)), resulted in the one-dimensional coordination polymers [Re2(DMBA)4(mu-O,O'-WO4)](infinity) (2) and [Re2(DMBA)4(mu-O,O'-1,4-(O2C)2C6H4)](infinity) (3), respectively. Both polymers display phosphorescence from a 3(delta --> delta*) state, which is significantly blue shifted from the phosphorescence previously observed for Re2(DMBA)4Cl2 type compounds.

Journal Article↗
PubMed2005

Push-pull effects and emission from ternary complexes of platinum(II), substituted terpyridines, and the strong-field cyanide ion.

As part of an effort to develop new lumaphors involving late transition metal ions, this report describes the synthesis and characterization of the first platinum(II) derivatives containing 2,2':6',2''-terpyridine (trpy) and cyanide as co-ligands. According to existing models, including cyanide in the coordination sphere should raise the energies and minimize the influence of short-lived d-d excited states that otherwise compromise the excited-state lifetime. Both [Pt(trpy)(CN)]+ and the 4'-cyano-2,2':6',2''-terpyridine analogue [Pt(CN-T)(CN)]+ are emissive in dichloromethane solution, but the signals are weak. Part of the problem is that the d-pi* charge-transfer excited states also rise in energy, so that the emission actually originates from a (3)pi-pi* state with a relatively low radiative rate constant. However, another member of the series, the 4'-dimethylamino-2,2':6',2''-terpyridine (dma-T) derivative [Pt(dma-T)(CN)]+, proves to be a very promising platform with an emission quantum yield of phi= 0.26 and an excited-state lifetime of tau = 22 micros in room-temperature, deoxygenated dichloromethane solution. In the dma-T complex the electron-rich dimethylamino substituent provides the basis for an emissive, but largely ligand-based, charge-transfer excited state. The orbital parentage is such that the photoluminescence persists in donating solvents like dimethylformamide, which ordinarily quenches d-pi* excited states in complexes of this type.

Cyanides↗
PubMed2004

A luminescent Pt(II) complex with a terpyridine-like ligand involving a six-membered chelate ring.

The ligand 2-(8'-quinolinyl)-1,10-phenanthroline (1) was prepared in 79% yield by the Friedlander condensation of 8-amino-7-quinolinecarbaldehyde and 8-acetylquinoline. The complex [Pt(1)Cl]+ was prepared and compared with the isomeric 2-(2'-quinolinyl)-1,10-phenanthroline (2) complex. An X-ray analysis indicated that the six-membered chelate ring in the tridentate complex resulted in a relief of angle strain as well as some non-planarity in the bound ligand 1. The control system for photophysical studies is [Pt3Cl]+ where denotes 2-(2'-pyridyl)-1,10-phenanthroline. Relative to the complex of 3, in dichloromethane solution [Pt(1)Cl]+ exhibits noticeably higher energy charge-transfer absorption but slightly lower energy emission. The gap between the onset of absorption and emission is larger because the emission from [Pt(1)Cl]+ originates from a triplet excited state with substantial intra-ligand character. At room temperature in deoxygenated dichloromethane, [Pt(1)Cl]+ has an excited-state lifetime of 310 ns vs. 230 ns for [Pt(1)Cl]+. Within the series, [Pt(1)Cl]+ also exhibits the largest activation barrier for thermally induced quenching at 2730 cm(-1) in fluid dichloromethane solution. However, the barrier is only about 50% larger than that found for [Pt(1)Cl]+. There is reduced ring strain in [Pt(1)Cl]+, but inter-ligand steric interactions weaken the ligand field.

Crystallography, X-Ray↗
PubMed2003

New dicationic porphyrin ligands suited for intercalation into B-form DNA.

This paper describes the synthesis and characterization of a new series of sterically nondemanding, dicationic porphyrins that exhibit novel DNA-binding interactions. Cationic porphyrins continue to be the focus of a great deal of effort because of the promise they have for use in photodynamic, antiviral, and anticancer therapies. The systems explored here include 5,15-di(N-methylpyridinium-4-yl)porphyrin (H2D4), 5,15-di(N-methylpyridinium-3-yl)porphyrin (H2D3), and 5,15-di(N-methylpyridinium-2-yl)porphyrin (H2D2), as well as Zn(D4) and Zn(D3), the zinc(II)-containing derivatives of H2D4 and H2D3, respectively. Viscometry studies, in conjunction with various spectroscopic techniques, reveal the nature of the adducts formed with DNA. Irrespective of the base composition, H2D4 and H2D3 bind to DNA by intercalation. The zinc derivatives Zn(D4) and Zn(D3) are also intercalators; however, the binding constants are smaller because uptake requires the loss of an axial ligand. The decisive roles that steric factors and structural rigidity play in shaping the adducts with DNA become clear. Sequences that contain mainly adenine-thymine base pairs easily depart from the canonical B-form DNA structure and generally accommodate bulky porphyrins in external binding sites. However, with the H2D3 and H2D4 systems, the steric requirements are so minimal that intercalation becomes the preferred mode of binding, even in [poly(dA-dT)]2. The intercalated form of the H2D2 isomer is less stable, probably because of frontal strain associated with the (N-methyl)pyridinium-2-yl groups. A qualitative energy-level diagram is useful for assessing the forces that influence binding and could guide the design of new porphyrin ligands.

Algorithms↗
PubMed2002

A superior polypyridine ligand for platinum(II) lumaphors. Methyl substituents with a large stereoelectronic influence.

This research deals with the synthesis and characterization of a new series of platinum(II) polypyridine complexes that incorporate a relatively rigid and hydrophobic ligand. The parent complex Pt(php)Cl(+), where php denotes 2-(2'-pyridyl)-1,10-phenanthroline, resembles Pt(trpy)Cl(+), where trpy denotes 2,2':6',2''-terpyridine, but is photoluminescent in solution. Hence php derivatives should prove to be superior tags and/or spectroscopic probes for biological systems. A theoretical analysis reveals some of the advantages of php over trpy as a platform. Due to a ligand pi system with a relatively small HOMO-LUMO gap, the emission from Pt(php)Cl(+) exhibits significant vibrational structure and a mixed (3)pi-pi*/(3)d-pi* orbital parentage. In deoxygenated dichloromethane solution the php complex exhibits an emission quantum yield of 3.1 x 10(-3) and an excited-state lifetime of 0.23 micros at room temperature. However, methyl groups have an unusually strong stereoelectronic influence, particularly at the 5,6-positions of the phenanthroline moiety. The platinum(II) complex with 2-(2'-pyridyl)-3,5,6,8-tetramethyl-1,10-phenanthroline is the best emitter with an emission yield of 0.055 and a lifetime of 9.3 micros in dichloromethane. Strongly donating solvents like dimethylformamide are potent quenchers of the emission. The methods of characterization used include absorption and emission spectroscopies, electrochemistry, and, in the case of [Pt[2-(2'-pyridyl)-4,7-dimethyl-1,10-phenanthroline]Cl]O(3)SCF(3), X-ray crystallography. Another intriguing finding is that methyl substituents have preferred orientations with respect to the phenanthroline ligand.

Journal Article↗
PubMed2002

Synthesis and structural characterization of Cu(I) and Ni(II) complexes that contain the bis[2-(diphenylphosphino)phenyl]ether ligand. Novel emission properties for the Cu(I) species.

The pseudotetrahedral complexes [Cu(NN)(DPEphos)]BF(4), where DPEphos = bis[2-(diphenylphosphino)phenyl]ether and NN = 1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-di-n-butylphenanthroline (3), or two dimethylcyanamides (4), and NiCl(2)(DPEphos) (5) have been synthesized and structurally characterized by X-ray crystallography and their solution properties examined by use of a combination of cyclic voltammetry, NMR spectroscopy, and electronic absorption spectroscopy. Complexes 1-4 possess a reversible Cu(II)/Cu(I) couple at potentials upward of +1.2 V versus Ag/AgCl. Compounds 1-3 exhibit extraordinary photophysical properties. In room-temperature dichloromethane solution, the charge-transfer excited state of the dmp (dbp) derivative exhibits an emission quantum yield of 0.15 (0.16) and an excited-state lifetime of 14.3 mus (16.1 mus). Coordinating solvents quench the charge-transfer emission to a degree, but the photoexcited dmp complex 2 retains a lifetime of over a microsecond in acetone, methanol, and acetonitrile.

Journal Article↗
PubMed2002

Simple Cu(I) complexes with unprecedented excited-state lifetimes.

This report describes new, readily accessible copper(I) complexes that can exhibit unusually long-lived, high quantum yield emissions in fluid solution. The complexes are of the form [Cu(NN)(POP)]+ where NN denotes 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp) or 2,9-di-n-butyl-1,10-phenanthroline (dbp) and POP denotes bis[2-(diphenylphosphino)phenyl] ether. Modes of characterization include X-ray crystallography and cyclic voltammetry. The complexes each have a pseudotetrahedral coordination geometry and a Cu(II)/Cu(I) potential upward of +1.2 V vs Ag/AgCl. In room-temperature dichloromethane solution, charge-transfer excited states of the dmp and dbp derivatives exhibit respective emission quantum yields of 0.15 and 0.16 and corresponding excited-state lifetimes of 14.3 and 16.1 mus, respectively. Despite the fact that coordinating solvents usually quench charge-transfer emission from copper systems, the photoexcited dmp (dbp) complex retains a lifetime of 2.4 mus (5.4 mus) in methanol.

Journal Article↗