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Photoexcited molecular trajectories on potential energy surfaces (PESs) prior to thermalization are intimately connected to the photochemical reaction outcome. The excited-state trajectories of a diplatinum complex featuring photo-activated metal–metal σ-bond formation and associated Pt−Pt stretching motions were detected in real time using femtosecond wide-angle X-ray solution scattering. The observed motions correspond well with coherent vibrational wavepacket motions detected by femtosecond optical transient absorption. Two key coordinates for intersystem crossing have been identified, the Pt−Pt bond length and the orientation of the ligands coordinated with the platinum centers, along which the excited-state trajectories can be projected onto the calculated PESs of the excited states. This investigation has gleaned novel insight into electronic transitions occurring on the time scales of vibrational motions measured in real time, revealing ultrafast nonadiabatic or non-equilibrium processes along excited-state trajectories involving multiple excited-state PESs.

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph2 P)C6 H4 )2 GeIV Cl2 ]PtII Cl2 and [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtIII Cl3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtI Cl with quantum yields of 1.7 % and 3.2 % for the GeIV -PtII and GeIII -PtIII isomers, respectively. Conversion of the GeIV -PtII isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the GeIII -PtIII isomer point to a ligand arene-Cl. charge-transfer complex as an intermediate.

The electronic structure and photophysical properties of two phosphorescent iridium(III) cyclometalated complexes is presented. The molecules were synthesized by cyclometalating the ligand 1,8-naphthalenebenzimidizole (NBI), to an iridium(III) metal center. Two NBI ligands were covalently attached along with a 1,10-phenanthroline (phen) ligand producing the [Ir(NBI)2(phen)](PF6) complex and three NBI ligands were used to prepare the corresponding tris-cyclometalate fac-Ir(NBI)3. The optical properties of these new Ir(III) molecules were investigated using density functional theory calculations, photoluminescence spectroscopy, and transient absorption spectroscopy. The molecules at the heart of this study were found to contain long-lived ligand-localized triplet excited states on the NBI species, featuring energies suitable for bimolecular photochemical reactions. Both iridium(III) chromophores possess excellent light absorptivity in the visible region of the spectrum with high photoluminescence quantum efficiencies approaching 30%.

Invited for this month's cover are the research groups of Prof. Rony S. Khnayzer at Lebanese American University and Prof. Felix (Phil) N. Castellano at North Carolina State University. The cover picture illustrates the absorption of visible light by a ruthenium bathophenanthroline MLCT chromophore followed by a sequence of electron transfer steps that ultimately leads to the efficient production of hydrogen gas from water. Read the full text of the article at 10.1002/cplu.201600227.

The electronic structure and photophysical properties of a luminescent IrIII bis-cyclometalated complex covalently attached to one 4-piperidinyl-1,8-naphthalimide (PNI) chromophore through a coordinated 1,10-phenanthroline, [Ir(ppy)2(phen-PNI)](PF6), is presented. This bichromophore represents a new class of visible light-harvesting IrIII complexes that exhibit markedly enhanced room-temperature excited-state lifetimes (τ = 8.8 ms) as a result of intervening ligand-centered triplet states present on the pendant naphthalimide chromophore. In this IrIII complex, the intense singlet fluorescence of the pendant PNI chromophore is nearly quantitatively quenched and was found to sensitize the IrIII metal/ligand-to-ligand charge-transfer (MLLCT) excited state. The excited state ultimately returns to the PNI chromophore as a long-lived excited triplet that disposes of its energy by equilibrating with the photoluminescent IrIII MLLCT excited state. Evidence of the excited-state equilibrium is provided through static and dynamic photoluminescence spectroscopy, transient absorption spectroscopy, and time-dependent density functional theory calculations.

The solvatochromic properties of [Pt(mesBIAN)(tda)] are studied in traditional molecular solvents and ionic liquids and duly compared along established empirical solvent parameter scales. The charge-transfer absorption band of [Pt(mesBIAN)(tda)] is determined to be primarily dependent upon solvent acidity and dipolarity. Notably, ionic liquids do not obey the same well-behaved trend as molecular solvents, highlighting the complexity and domain (nano)segregation inherent to ionic liquids.

A series of cyclometalated RuII coordination compounds of the general structural formula [Ru(bpy)2(C∧N)]PF6 {C∧N = 2-phenylpyridine (1), 2-(2,4-difluorophenyl)pyridine (2), 2-(4-methoxyphenyl)-5-methylpyridine (3), benzo[h]quinoline (4); bpy = 2,2′-bipyridine} have been synthesized, structurally and electrochemically characterized, and examined by using a battery of spectroscopic techniques. The combination of static and dynamic photoluminescence at room temperature and 77 K, resonance Raman spectroscopy, cyclic voltammetry, spectroelectrochemistry, and ultrafast transient absorption spectroscopy reveal that – although the nature of the cyclometalating ligand substantially affects the oxidation potential at the metal center – the lowest-energy metal-to-ligand charge-transfer excited state always retains pure Rubpy character across this series of molecules, and the cyclometalating subunit plays the role of ancillary ligand.

A diimine ligand tethered to anthracene in the 9-position, 4′-(9-anthrylethyl)-4-methyl-2,2′-bipyridine (bpy-An), was dimerized through cycloaddition photochemistry. The resultant head-to-tail photodimer (bpy-PD) was used as a bridging ligand in the preparation of a new dinuclear RuII complex, [Ru(dmb)2(bpy-PD)Ru(dmb)2]4+ (dmb = 4,4′dimethyl-2,2′-bipyridine). The corresponding mononuclear species containing anthracene ([Ru(dmb)2(bpy-An)]2+ was also synthesized and serves as a model compound in this study. UV photolysis (λ

Measurements of DNA dynamics are typically limited to the nanosecond timescale because of the nanosecond decay times of commonly used fluorophores such as ethidium bromide and acridine derivatives. We show that the time-resolved anisotropy measurements can be extended to the submicrosecond timescale using metal-ligand complexes. The ruthenium complex [Ru(2,2′,-bipyridine)2(dipyrido[3,2-a : 2′,3′-c]phenazine)]2+, or [Ru(bpy)2(dppz)]2+, was found to display high anisotropy near 0.2, at −60°C in 100% glycerol, when excited in its long-wavelength absorption bands. The decay time of [Ru(bpy)2(dppz)]2+ when bound to DNA is over 100 ns, allowing intensity to be measured to over 400 ns. Other Ru complexes display still longer lifetimes to 750 ns when bound to DNA. This class of fluorophores should enable measurement of DNA dynamics over a wide range of times (from 1 ns to several μs), which were previously inaccessible using time-resolved fluorescence. © 1995 John Wiley & Sons, Inc.

Electron and energy transfer processes from CuI MLCT excited states are reviewed. New results demonstrate clearly that these excited states undergo oxidative electron transfer quenching and energy transfer processes. The yields and dynamics of these processes have been spectroscopically quantified. Interfacial electron transfer from CuI MLCT excited states to wide band gap semiconductors has been observed. When utilized in photoelectrochemical cells, this interfacial electron transfer process provides a means for the conversion of light directly into electrical power.

Resonance energy transfer from tris(2,2′-bipyridyl)ruthenium (II) ([Ru(bpy)3]2+) to nile blue A is demonstrated in aqueous solution in the presence of sodium dodecyl sulfate (SDS). At SDS concentrations below the critical micelle concentration, aggregates that permit energy transfer between these dyes at optically dilute (10 μM) concentrations with nearly 100% efficiency are formed. The disparity between the lifetimes of the donor and acceptor results in the lengthening of the photoluminescence lifetime of the sensitized emission observed from nile blue A. Time-resolved luminescence measurements confirm that the long-lived components of the emission originate from sensitized acceptor emission.

We developed a water-soluble luminescent probe for dissolved oxygen. This probe is based on (Ru[dpp(SO(3)Na)(2)](3))Cl(2), which is a sulfonated analogue of the well-known oxygen probe (Ru[dpp](3))Cl(2). The compound dpp is 4,7-diphenyl-1,10-phenanthroline and dpp(SO(3)Na)(2) is a disulfonated derivative of the same ligand. In aqueous solution in the absence of oxygen (Ru[dpp(SO(3)Na)(2)](3))Cl(2) displays a lifetime of 3.7 μs that decreases to 930 ns on equilibrium with air and 227 ns on equilibrium with 100% oxygen. The Stern–Volmer quenching constant is 11330 M(−1). This high oxygen-quenching constant means that the photoluminescence of Ru(dpp[SO(3)Na](2))(3)Cl(2) is 10% quenched at an oxygen concentration of 8.8 × 10(−6) M, or equilibration with 5.4 torr of oxygen. The oxygen probe dissolved in water displays minimal interactions with lipid vesicles composed of dipalmityl-l-α-phosphatidyl glycerol but does appear to interact with human serum albumin. The absorption maximum near 480 nm, long lifetime and large Stokes’ shift allow this probe to be used with simple instrumentation based on a light-emitting diode light source, allowing low-cost oxygen sensing in aqueous solutions. To the best of our knowledge this is the first practical water-soluble oxygen sensor.