Scale-Up of Continuous Metallaphotoredox Catalyzed C-O Coupling to a 10 kg-Scale Using Small Footprint Photochemical Taylor Vortex Flow Reactors.

We report the development and optimization of a scalable flow process for metallaphotoredox (Ir/Ni) C-O coupling, a mild and efficient approach for forming alkyl-aryl ethers, a common motif in medicinal and process chemistry settings. Time-resolved infrared spectroscopy (TRIR) highlighted the amine as the major quencher of the photocatalyst triplet excited state, along with the formation of an Ir(II) species that, in the presence of the Ni cocatalyst, has its lifetime shortened, suggesting reductive quenching of Ir(III)*, followed by reoxidation facilitated by the Ni cocatalyst. TRIR and batch reaction screening was used to develop conditions transferrable to flow, and many processing benefits of performing the reaction in flow were then demonstrated using a simple to construct/operate, small-footprint FEP coil flow reactor, including short (<10 min) space times and reduced catalyst loadings (down to 0.

Wavelength dependent photoextrusion and tandem photo-extrusion reactions of ninhydrin bis-acetals for the synthesis of 8-ring lactones, benzocyclobutenes and orthoanhydrides.

Ninhydrin bis-acetals give access to 8-ring lactones, benzocyclo-butenes and spirocyclic orthoanhydrides through photoextrusion and tandem photoextrusion reactions. Syntheses of fimbricalyxlactone B, isoshihunine and numerous biologically-relevant heterocycles show the value of the methods, while TA-spectroscopy and TD-DFT studies provide mechanistic insights on their wavelength dependence.

Understanding the factors controlling the photo-oxidation of natural DNA by enantiomerically pure intercalating ruthenium polypyridyl complexes through TA/TRIR studies with polydeoxynucleotides and mixed sequence oligodeoxynucleotides.

Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)(dppz)] in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at 1700 cm for the guanine radical cation and a band centered at 515 nm in the TrA for the reduced ruthenium complex.

Generation of Microsecond Charge-Separated Excited States in Rhenium(I) Diimine Complexes: Driving Force Is the Dominant Factor in Controlling Lifetime.

A transition-metal-based donor-(linker)-acceptor system can produce long-lived charge transfer excited states using visible excitation wavelengths. The ground- and excited-state photophysical properties of a series of [ReCl(CO)(dppz-(linker)-TPA)] complexes, with varying donor and acceptor energies, have been systematically studied using spectroscopic techniques (both vibrational and electronic) supported by computational chemistry. The long-lived excited state is ILCT in nature for all complexes studied, characterized through transient absorption and emission, transient resonance Raman (TR), and time-resolved infrared (TRIR) spectroscopy and TDDFT calculations.

Monitoring the Formation and Reactivity of Organometallic Alkane and Fluoroalkane Complexes with Silanes and Xe Using Time-Resolved X-ray Absorption Fine Structure Spectroscopy.

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO), we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding.

Author Correction: Additive manufacture of complex 3D Au-containing nanocomposites by simultaneous two-photon polymerisation and photoreduction.

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Probing the Carbon-Hydrogen Activation of Alkanes Following Photolysis of Tp'Rh(CNR)(carbodiimide): A Computational and Time-Resolved Infrared Spectroscopic Study.

Carbon-hydrogen bond activation of alkanes by Tp'Rh(CNR) (Tp' = Tp = trispyrazolylborate or Tp* = tris(3,5-dimethylpyrazolyl)borate) were followed by time-resolved infrared spectroscopy (TRIR) in the υ(CNR) and υ(B-H) spectral regions on Tp*Rh(CNCHCMe), and their reaction mechanisms were modeled by density functional theory (DFT) on TpRh(CNMe). The major intermediate species were: κ-η-alkane complex (1); κ-η-alkane complex (2); and κ-alkyl hydride (3). Calculations predict that the barrier between 1 and 2 arises from a triplet-singlet crossing and intermediate 2 proceeds over the rate-determining C-H activation barrier to give the final product 3.

Additive manufacture of complex 3D Au-containing nanocomposites by simultaneous two-photon polymerisation and photoreduction.

The fabrication of complex three-dimensional gold-containing nanocomposite structures by simultaneous two-photon polymerisation and photoreduction is demonstrated. Increased salt delivers reduced feature sizes down to line widths as small as 78 nm, a level of structural intricacy that represents a significant advance in fabrication complexity. The development of a general methodology to efficiently mix pentaerythritol triacrylate (PETA) with gold chloride hydrate (HAuCl∙3HO) is reported, where the gold salt concentration is adjustable on demand from zero to 20 wt%.

Thionated naphthalene diimides: tuneable chromophores for applications in photoactive dyads.

Varying the degree of thionation of a series of naphthalene diimide (NDI) and naphthalic imide (NI) phenothiazine dyad systems affords a systematic approach for tuning the system's donor-acceptor energy gap. Each dyad was compared to model NDI/NI systems and fully characterised through single crystal X-ray diffraction, NMR, cyclic voltammetry, electron paramagnetic resonance (EPR), transient absorption spectroscopy (TA), time-resolved infra-red spectroscopy (TRIR) and DFT. The measurements reveal that thionation increases both electron affinity of the NDI/NI acceptor dyad component and accessibility of the singly or doubly reduced states.

Alteration of Intraligand Donor-Acceptor Interactions Through Torsional Connectivity in Substituted Re-dppz Complexes.

The ground- and excited-state properties of a series of [ReCl(CO)(dppz)] complexes with substituted donor groups were investigated. Alteration of donor-acceptor communication through modulation of torsional angle and the number and nature of the donor substituents allowed the effects on the photophysical properties to be characterized though both computational and spectroscopic techniques, including time-dependent density functional theory and resonance Raman and time-resolved infrared spectroscopy. The ground-state optical properties show significant variation as a result of donor group modulation, with an increased angle between the donor and acceptor blue-shifting and depleting the intensity of the lowest-energy transition, which is consistently intraligand charge transfer (ILCT) in nature.

Excited States of Triphenylamine-Substituted 2-Pyridyl-1,2,3-triazole Complexes.

A new 2-pyridyl-1,2,3-triazole (pytri) ligand, TPA-pytri, substituted with a triphenylamine (TPA) donor group on the 5 position of the pyridyl unit was synthesized and characterized. Dichloroplatinum(II), bis(phenylacetylide)platinum(II), bromotricarbonylrhenium(I), and bis(bipyridyl)ruthenium(II) complexes of this ligand were synthesized and compared to complexes of pytri ligands without the TPA substituent. The complexes of unsubstituted pytri ligands show metal-to-ligand charge-transfer (MLCT) absorption bands involving the pytri ligand in the near-UV region.

Photo-reduction of CO2 Using a Rhenium Complex Covalently Supported on a Graphene/TiO2 Composite.

One of the promising solutions for decreasing atmospheric CO2 is artificial photosynthesis, in which CO2 can be photoconverted into solar fuels. In this study, a rhenium complex Re(PyBn)(CO)3 Cl (PyBn=1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) was covalently grafted onto the surface of reduced graphene oxide (rGO). This was further combined with TiO2 to fabricate a novel catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl for CO2 photo-reduction.

Long-Lived Charge Transfer Excited States in HBC-Polypyridyl Complex Hybrids.

The synthesis of two bipyridine-hexa-peri-hexabenzocoronene (bpy-HBC) ligands functionalized with either (t)Bu or C12H25 and their Re(I) tricarbonyl chloride complexes are reported and their electronic properties investigated using spectroscopic and computational methods. The metal complexes show unusual properties, and we observed the formation of a long-lived excited state using time-resolved infrared spectroscopy. Depending on the solvent, this appears to be of the form Rebpy(•-)HBC(•+) or a bpy-centered π,π* state.

Can aliphatic anchoring groups be utilised with dyes for p-type dye sensitized solar cells?

A series of novel laterally anchoring tetrahydroquinoline derivatives have been synthesized and investigated for their use in NiO-based p-type dye-sensitized solar cells. The kinetics of charge injection and recombination at the NiO-dye interface for these dyes have been thoroughly investigated using picosecond transient absorption and time-resolved infrared measurements. It was revealed that despite the anchoring unit being electronically decoupled from the dye structure, charge injection occurred on a sub picosecond timescale.

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.

Comparison of rhenium-porphyrin dyads for CO photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy.

We report a study of the photocatalytic reduction of CO to CO by zinc porphyrins covalently linked to [Re(2,2'-bipyridine)(CO)L] moieties with visible light of wavelength >520 nm. contains an amide CHNHC(O) link from porphyrin to bipyridine (Bpy), contains an additional methoxybenzamide within the bridge CHNHC(O)CH(OMe)NHC(O), while has a saturated bridge CHNHC(O)CH; each dyad is studied with either L = Br or 3-picoline. The syntheses, spectroscopic characterisation and cyclic voltammetry of and are described.

Probing organometallic reactions by time-resolved infrared spectroscopy in solution and in the solid state using quantum cascade lasers.

The photochemistry and photophysics of metal carbonyl compounds (W(CO)6, Cp*Rh(CO)2 (Cp* = η(5)-C5Me5), and fac-[Re(CO)3(4,4'-bpy)2Br] [bpy = bipyridine]) have been examined on the nanosecond timescale using a time-resolved infrared spectrometer with an external cavity quantum cascade laser (QCL) as the infrared source. We show the photochemistry of W(CO)6 in alkane solution is easily monitored, and very sensitive measurements are possible with this approach, meaning it can monitor small transients with absorbance changes less than 10(-6) ΔOD. The C-H activation of Cp*Rh(CO)(C6H12) to form Cp*Rh(CO)(C6H11)H occurs within the first few tens of nanoseconds following photolysis, and we demonstrate that kinetics obtained following deconvolution are in excellent agreement with those measured using an ultrafast laser-based spectrometer.

Study of picosecond processes of an intercalated dipyridophenazine Cr(III) complex bound to defined sequence DNAs using transient absorption and time-resolved infrared methods.

Picosecond transient absorption (TA) and time-resolved infrared (TRIR) measurements of rac-[Cr(phen)2(dppz)](3+) () intercalated into double-stranded guanine-containing DNA reveal that the excited state is very rapidly quenched. As no evidence was found for the transient electron transfer products, it is proposed that the back electron transfer reaction must be even faster (<3 ps).

Carbon-hydrogen activation of cycloalkanes by cyclopentadienylcarbonylrhodium--a lifetime enigma.

Carbon-hydrogen bond activation reactions of four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) by the Cp'Rh(CO) fragments (Cp' = η(5)-C5H5 (Cp) or η(5)-C5Me5 (Cp*)) were modeled theoretically by combining density functional and coupled cluster theories, and their reaction rates were measured by fast time-resolved infrared spectroscopy. The reaction has two steps, starting with the formation of a σ-complex intermediate, followed by oxidative addition of the C-H bond by the rhodium. A range of σ-complex stabilities among the electronically unique C-H bonds in a cycloalkane were calculated and are related to the individual strengths of the C-H bond's interactions with the Rh fragment and the steric repulsion that is incurred upon forming the specific σ-complex.

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.

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.

Promoting charge-separation in p-type dye-sensitized solar cells using bodipy.

The viability of applying bodipy sensitisers to NiO-based p-type dye-sensitised solar cells (p-DSCs) has been successfully demonstrated. The triphenylamine donor-bodipy acceptor design promotes a long-lived charge-separated state which is difficult to achieve with NiO-based devices. The current was above 3 mA cm(-2) and the IPCE was 28%.

Photophysics and electrochemistry of a platinum-acetylide disubstituted perylenediimide.

The synthesis and photophysical study of a perylene diimide (PDI) functionalised with platinum acetylide units of the type, trans{-C≡C-Pt(PBu3)2-C≡C-Ph} and comparison with a phenylacetylide substituted model compound are reported. The model compound demonstrates typical perylene absorption and photoluminescence spectra characteristic of singlet excited state formation and decay. The Pt-substitution, however, appears to induce spin-orbit coupling into the chromophore and giving rise to a triplet excited state which was confirmed by transient absorption measurements.

Energy dispersive XAFS: characterization of electronically excited states of copper(I) complexes.

Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2](+) (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns.

Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: a detailed electrochemical, spectroscopic and computational study.

The dinuclear complex [{Ru(CN)(4)}(2)(μ-bppz)](4-) shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH(2)Cl(2). In CH(2)Cl(2) the separation between the successive Ru(II)/Ru(III) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state.