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The synthesis, structural and photophysical characterisation of four tricarbonyl rhenium(i) complexes bound to 1,10-phenanthroline and a tetrazolato ancillary ligand are reported. The complexes are differentiated by the nature (hydroxy or methoxy) and position (meta or para) of the substituent attached to the phenyl ring in conjugation to the tetrazole ring. The complexes exhibit phosphorescence emission from triplet charge transfer excited states, with the maxima around 600 nm, excited state lifetime decays in the 200-300 ns range, and quantum yield values of 4-6% in degassed acetonitrile solutions. The nature and position of the substituent does not significantly affect the photophysical properties, which remain unchanged even after deprotonation of the hydroxide group on the phenol ring. The interpretation of the photophysical data was further validated by resonance Raman spectroscopy and time-dependent density functional theory calculations. All the complexes are internalised within cells, albeit to variable degrees. As highlighted by a combination of flow cytometry and confocal microscopy, the species display diffuse cytoplasmic localisation except for the complex with the hydroxy functional group at the para position, which reveals lower accumulation in cells and more pronounced punctate staining. Overall, the complexes displayed low levels of cytotoxicity.

We present a simple and effective way of using metal and metal–ligand modifications to tune the electrochemical and optical properties of conducting polymers. To that end, a polyterthiophene functionalized with terpyridine moieties was synthesized and then the resulting film's surface or bulk was modified with different metal ions, namely Fe2+, Zn2+ and Cu2+ and terpyridine. The modification of the terpyridine functionalized polyterthiophene film by Fe2+ increased the absorptivity and electrochemical capacitance of the conducting polymer, and improved its conjugation. Further modification by Zn2+ and Cu2+ resulted in dramatically different spectroelectrochemical properties of the film. Moreover, the influence of the solvents (ACN and 1 : 1 ACN : H2O) in conjunction with the metal ion applied for the modification was found crucial for the electrochemical and optical properties of the films. Published version

Design of nanometer scale artificial light harvesting and charge separating proteins enables reengineering to overcome the limitations of natural selection for efficient systems that better meet human energetic needs., Natural selection in photosynthesis has engineered tetrapyrrole based, nanometer scale, light harvesting and energy capture in light-induced charge separation. By designing and creating nanometer scale artificial light harvesting and charge separating proteins, we have the opportunity to reengineer and overcome the limitations of natural selection to extend energy capture to new wavelengths and to tailor efficient systems that better meet human as opposed to cellular energetic needs. While tetrapyrrole cofactor incorporation in natural proteins is complex and often assisted by accessory proteins for cofactor transport and insertion, artificial protein functionalization relies on a practical understanding of the basic physical chemistry of protein and cofactors that drive nanometer scale self-assembly. Patterning and balancing of hydrophobic and hydrophilic tetrapyrrole substituents is critical to avoid natural or synthetic porphyrin and chlorin aggregation in aqueous media and speed cofactor partitioning into the non-polar core of a man-made water soluble protein designed according to elementary first principles of protein folding. This partitioning is followed by site-specific anchoring of tetrapyrroles to histidine ligands strategically placed for design control of rates and efficiencies of light energy and electron transfer while orienting at least one polar group towards the aqueous phase.

Complexes of the type [M(ppy)(big)], (where M = Pt(II) and Pd(II), ppy is 2-phenylpyridine and big is a 1,5-diarylbiguanide) have been prepared and characterised in solution and in the solid state. The big ligand possesses a DAD triple hydrogen bonding array that is designed to facilitate assembly of the complexes with complementary organic components. In DMF solution and in the solid state, the complexes are found to adopt a syn–syn conformer of the big ligand to allow hydrogen bonding of DMF molecules to pairs of NH donors. DFT calculations correctly predict this conformation, but only when DMF molecules are explicitly included in the calculation. The electronic spectral properties of the Pt(II) complexes are largely independent of the big ligand and are concentration independent in DMF solution, with TD-DFT calculations showing that the emission comes from the [Pt(ppy)] luminophore. In the presence of 1,8-naphthalimide and barbital derivatives, the big ligand adopts the alternate anti–anti conformer, which enables a triple hydrogen bonding motif. Notably, the two components adopt significantly non-planar orientations, a feature which will be important in their use as tectons for rational crystal engineering applications. Complexes of the type [Pd(ppy)(Hbig)]OAc, are also described, where the acetate anion is hydrogen bonded to the protonated Hbig ligand which adopts the anti–anti conformation.

A 2,2'-bipyridine-appended ferrocene rotor, 1,1'-di(5-yl-ethynyl-2,2'-bipyridine)ferrocene, can be switched from a folded/stacked (syn) conformation to an extended/unstacked (anti) conformation by the addition of [Cu(CH3CN)4](PF6) and 6,6'-dimesityl-2,2'-bipyridine. This extension and contraction process was completely reversible and could be triggered either chemically or electrochemically.

The purpose of this work is to investigate the origin of improved photovoltaic performance of a series of di-chromophoric carbazole-substituted porphyrin dyes employed as sensitizers in dye-sensitized solar cells. Five di-chromophoric zinc porphyrin dyes with the same porphyrin core, a carbazole unit attached in the meso-position through a phenylethenyl linkage, and substituents spanning a range of electron affinities, in an attempt to tune the electronic level of the carbazole unit, have been synthesized (CZPs). Density functional theory (DFT) calculations predicted the nature of the electronic transitions observed in the CZP systems, showing a large degree of orbital mixing. In contrast, UV-vis absorption, resonance Raman spectroscopy and differential pulse voltammetry investigations suggested negligible interaction between the porphyrin and carbazole chromophores. Carbazole substitution led to a moderate increase in photon absorption intensity within the ∼300 nm to 400 nm wavelength region, a smaller but broader Soret band absorption and slightly increased photon absorption intensity in the 550 nm to 650 nm Q band region. Despite the rather small changes in light harvesting and negligible changes in the HOMO/LUMO electronic levels, the photovoltaic performance of the new dyes is increased by as much as 30% compared to the single chromophore Zn porphyrin dye 5-(4-(2-cyano-2-carboxyethenyl)phenyl-15-phenyl-10,20-bis(2,4,6-trimethylphenyl)porphyrinato zinc(II) (ZP1), leading to over 6% power conversion efficiencies (PCEs). Both open circuit voltage (VOC) and short circuit current (JSC) have increased. The increased VOC is attributed to increased electron lifetimes due to a steric blocking effect. Analysis of the increased short circuit current (ΔJSC) showed that only less than 10% of ΔJSC originates from increased light absorption under simulated air mass 1.5 illumination, while the rest of the improvements are attributed to a steric effect enhancing the electron injection efficiency. These results suggest that developing non-conjugated multichromophoric dyes can lead to simultaneous increases in both the photocurrent and the photovoltage of dye-sensitized solar cells.

The synthesis of self-assembled metallosupramolecular architectures has been of steadily growing interest in recent years due to their diverse applications. Appending additional functionality to the ligands of these architectures has been limited as this often involves incorporation of coordinating groups that can potentially disrupt formation of the desired structure. Herein we report the use of the facile, functional group tolerant and high yielding CuAAC ‘click’ reaction to attach a variety of functional moieties to a tripyridyl ligand system. Despite the presence of the potentially coordinating 1,2,3-triazole rings, self-assembly of quadruply-stranded dipalladium(II) cage architectures in the presence of Pd(II) ions was almost universally observed for the functionalised “click” ligands. The only system which did not assemble into the expected cage featured a 2-(1,2,3-triazol-4-yl)pyridine binding pocket which sequestered the Pd(II) ions. Blocking this chelating pocket with an inert [Re(CO)3Cl] moiety restored the ability of the ligand to self-assemble into the desired quadruply-stranded dipalladium(II) cage, generating a heterometallic cage architecture. All ligands and cage architectures have been characterised using 1H, 13C and DOSY NMR, IR, UV-Vis and emission spectroscopies, mass spectrometry and in some cases by X-ray crystallography. Whilst the parent cage system is devoid of useful physical properties and displays a limited range of solubility, the CuAAC methodology provides a facile method to enhance the cage's properties. A variety of fluorescent, redox active and biologically relevant species have been appended to the external surface of these cages. These groups enabled the generation of a series of aqueous soluble, fluorescent and electrochemically active Pd2L4 cages in a modular fashion.

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.

1,5-Diarylbiguanides, where the aryl groups are phenyl (HL1), 3,5-dimethylphenyl (HL2), 3,5-dimethoxyphenyl (HL3), 4-t-butylphenyl (HL4) or 4-bromophenyl (HL5), have been prepared and characterised. HL3 and HL5 have been structurally characterised by X-ray crystallography, which shows them to adopt the expected tautomeric form for biguanides. They have extensive hydrogen-bonding interactions in the solid state, involving the biguanide NH groups supported by, in the case of HL3, the OCH3 aryl substituents or, in the case of HL5, Br···Br interactions. Reactions of HL1–HL4 with Ni(BF4)2 gives complexes of the type [Ni(HL)2](BF4)2, while reactions of HL1–HL4 with Ni(BF4)2 and triethylamine give neutral complexes of the type [Ni(L)2], where the biguanide ligand has been deprotonated at the N(ring) nitrogen. Both series of complexes were characterised in solution and the solid state. Cyclic voltammetry shows a largely irreversible Ni(II)/Ni(III) oxidation which becomes easier by ca. 70 mV upon ligand deprotonation, with more subtle variations resulting from the changes in aryl ring substituents. Infrared and 1H NMR spectroscopies both provide evidence for ligand deprotonation leading to the chelate ring becoming increasingly aromatised. X-ray crystallographic analyses of five of the complexes also show changes in bond lengths and angles within the chelate ring, consistent with increased electron delocalisation. A variety of hydrogen bonding motifs involving the complex ions, counterions and solvent molecules are found. The results of DFT calculations on both cationic and neutral complexes provide calculated structures consistent with the experimental ones and these, along with the results of vibrational spectroscopic studies, provide further evidence for increased aromatisation upon deprotonation. The potential for the complexes to act as tectons for the rational assembly of hydrogen bonded metallosupramolecules is discussed and the X-ray structure of such an assembly, between [Ni(L3)2] and 1,8-naphthalimide, is presented.

This critical review discusses the applicability of vibrational spectroscopic techniques, specifically Raman and mid-infrared, to the study of molecule-based electronics through a series of examples. We focus on a number of devices currently of interest, such as solar cells, organic light emitting diodes, molecular junctions, switches and transistors. Infrared and Raman spectroscopic techniques and their variations, the main focus of this article, can be used to investigate properties such as crystallinity, multiphasic distributions in three dimensions, as well as lifetimes, structures and energetics of excited-states on ultrashort to very long timescales (210 references).

A series of tetraphenylporphyrins appended at the β-pyrrolic position with an ethynylphenylene- or ethynylpyridine-substituent have been subjected to spectroscopic and density functional theory (DFT) analyses. The mean absolute deviation between corresponding experimental and DFT-derived vibrational spectra is up to 10.2 cm(-1), suggesting that the DFT B3LYP/6-31G(d) method provides an accurate model of the β-substituted porphyrin systems. The configuration interactions that give rise to prominent electronic absorptions have been calculated using time-dependant DFT (TD-DFT) and have been rationalized with reference to the energy and topology of DFT calculated molecular orbitals. As the electron withdrawing capacity of the β-substituent increases the LUMO orbital gains appreciable amplitude over the substituent moiety and is stabilised. This represents a departure from the assumptions underpinning the Gouterman four-orbital model, resulting in atypical electronic absorption spectra. This phenomenon is also manifested in the enhancement patterns of the resonance Raman spectra insofar as B-band excitation engenders an enhancement of substituent based modes. These observations demonstrate that the β-substituent exerts an appreciable electronic influence on the porphyrin π-electron system and provides a means of introducing charge-transfer character to prominent electronic transitions.

The resonance Raman spectra of the ground- and lowest excited-states for a series of binuclear copper(I) complexes with bridging ligands based on 2,3-di-(2-pyridyl)quinoxaline have been measured. Analyses of the ground-state resonance Raman spectra show strong enhancement of an inter-ring stretching mode and quinoxaline-based modes; consistent with the Frank–Condon state having bonding changes about the copper(I) centre and on the quinoxaline ring system. The electronic absorption data also suggest the initially formed MLCT-state is localised towards the quinoxaline ring system. The excited-state resonance Raman spectroscopy shows similar spectral features for complexes which have substituent changes at the pyridyl rings of the bridging ligand. They show spectra associated with the radical anion of the bridging ligand. This is consistent with the formation of an excited-state which is metal-to-ligand charge-transfer in nature and where the radical anion is localised on the quinoxaline ring system of the bridging ligand.

Binuclear complexes of the type [(bpy)2Ru(BL)Cu(PPh3)2]3+, where bpy = 2,2′-bipyridine, BL = 2,3-di-2-pyridylpyrazine (dpp), 2,3-di-2-pyridylquinoxaline (dpq), or 6,7-dimethyl-2,3-di-2-pyridylquinoxaline (dpqMe2), were readily formed by the reaction of [Cu(PPh3)4]+ with mononuclear complexes [Ru(bpy)2(BL)]2+. The binuclear complexes are stable in CH2Cl2 solution at concentrations above 10–3 mol dm–3 having equilibrium constants for formation in the range 1000–2500 dm3 mol–1. Single crystal structures for [(bpy)2Ru(dpp)Cu(PPh3)2]3+ and [(bpy)2Ru(dpqMe2)Cu(PPh3)2]3+ show distortions of the bridging ligand in the form of twisting and splaying of the ring systems. Electrochemical and UV/Visible data suggest the {Cu(PPh3)2}+ moiety has little affect in stabilising the BL π* orbital. Resonance Raman spectra show the bichromophoric nature of the visible absorptions of the heteroleptic complexes; both bpy and BL ligand vibrations are enhanced depending on the excitation wavelength. Observation of a Ru–N vibration suggests that the dominant transition in the visible region is Ru(dπ)→BL(π*) CT.

Several new ferrocene-functionalised porphyrins and a ruthenocene-functionalised porphyrin have been synthesized and studied using electrochemistry, electronic absorbance and resonance Raman spectroelectrochemical techniques. The porphyrin and ferrocene are observed to have limited effect on each other with the properties of the porphyrin dominating the spectroscopy of these molecules.

The electrochemical and spectral properties of copper(I) complexes with binaphthyridine ligands, bn and tbn (where bn = 2,2′-1,8-binaphthyridine, tbn = 3,3′-trimethylene-2,2′-1,8-binaphthyridine), have been studied. The complexes are [Cu(bn)2]+ 1, [Cu(tbn)2]+ 2, [Cu(bn)(PPh3)2]+ 3 and [Cu(tbn)(PPh3)2]+ 4. Reduction of 1–3 results in the formation of radical anion species involving the ligands. Reduction of 4 results in decomposition. For 3– strong near infrared absorptions (1000 nm) are observed suggesting a bn˙– radical anion species, in which the redox MO extends across the entire ligand. For 2– absorptions at 750 nm suggest a redox MO which is much less extensive and localised on a single naphthyridine unit of the tbn ligand. Reduction of 1 is complicated by the presence of two closely lying reduction waves. Application of a reducing potential resulted in spectral features similar to those observed for 3–. However, further reduction showed spectral features similar to those of 2–. The crystal structure of 3·BF4 was determined by single-crystal X-ray diffraction.

A number of mononuclear rhenium(I) complexes have been prepared and their physical properties and excited-state and spectroelectrochemical resonance-Raman spectra studied. These compounds have the general formula [Re(CO)3Cl(L)], where L can be 2,3-di(2-pyridyl)quinoxaline (dpq), 2-(2-pyridyl)quinoxaline (pq) or 5-methyl-2,3-di(2-pyridyl)quinoxaline (mdpq). The structure of [Re(CO)Cl(dpq)] was determined by single-crystal X-ray diffraction. The NMR data for complexes with dpq and mdpq suggest the unbound pyridyl is shielding protons on the bound pyridyl moiety. The resonance-Raman spectra of the reduced complexes show some polarisation of electron density towards the bound pyridyl ring. The excited states have very similar spectral features to those of the reduced complexes. This suggests that electrochemically prepared redox states model the metal-to-ligand charge-transfer state well, for these systems.

Copper(I) and rhenium(I) complexes with the ligand dipyrido[3,2,-a:2′,3′-c]phenazine (dppz) and a number of substituted analogues have been synthesized. Their spectroscopic and electrochemical properties have been studied. It is found that the lowest-energy transition for the complexes is metal-to-ligand charge transfer (MLCT) in nature. This has a low Iµ value. The resonance Raman spectra for the complexes show groups of bands that shift with substitution at the ligand and groups that remain unchanged in wavenumber. Electrochemical reduction of the complexes resulted in the formation of the ligand radical anion species for all but one system. This was confirmed by UV/VIS spectroelectrochemistry. Using resonance Raman spectroelectrochemistry marker bands have been identified for the radical anion species. The excited states of the complexes were studied by excited-state electronic absorption and time-resolved resonance Raman techniques. The former spectra are ambiguous as to the nature of the lowest excited state; however, the latter spectra confirm that this state is ligand-centred for complexes of dppz and its 11-methyl derivative. Complexes with the 11-nitro derivative appear to form excited states that are MLCT in nature.

The spectroscopy of electrochemically reduced ruthenium(II) complexes with 2,2′-biquinoline and 2,2′-binaphthyridine ligands have been investigated. These compounds are: [Ru(bn)(bpy)2][BF4]2 (where bn = 2,2′-bi-1,8-naphthyridine and bpy = 2,2′-bipyridyl); [Ru(dbn)(bpy)2][BF4]2 (where dbn = 3,3′-dimethylene-2,2′-bi-1,8-naphthyridine); [Ru(dbn)3][BF4]2; [Ru(dbq)(bpy)2][BF4]2 (where dbq = 3,3′-dimethylene-2,2′-biquinoline). Resonance Raman spectra of the parent species showed the bichromophoric nature of the visible absorptions of the heteroleptic complexes; both bpy and non-bpy ligand vibrations are enhanced depending on the excitation wavelength. Changes in the electronic absorption spectra for the complexes upon electrochemical reduction suggest the reducing electron is localised on the non-bpy ligand. For the complexes with the dimethylenebinaphthyridine ligand the second reduction also appears localised on the non-bpy ligand. Resonance Raman spectra of the reduced species confirm that the first and second reduction are based on the dbn ligand. Single crystal structures of [Ru(bn)(bpy)2][BF4]2 and [Ru(dbn)(bpy)2][BF4]2 have been determined and significant distortions of the ligands are apparent.

We report the first example of a conducting polymer with a merocyanine incorporated into the polymer backbone by electropolymerisation of a spiropyran moiety covalently linked between two alkoxythiophene units. Utilising the known metal coordination capabilities of merocyanines, introduction of cobalt ions into the electropolymerisation led to an enhancement of the conductivity, morphology and optical properties of the polymer films.

A bisporphyrin substituted bipyridine ligand and several metal derivatives are described.

The functionality of anhydrous milk fat (AMF) is determined from solid fat content (SFC) and triacylglycerol (TG) profiles, parameters traditionally measured using nuclear magnetic resonance and high pressure liquid chromatography respectively. Raman spectroscopy coupled with partial least squares (PLS) analysis has been assessed as an alternative method for SFC and TG class quantification. Sample temperature at which the Raman spectra were collected, method of spectral preprocessing and type of PLS analysis were all investigated and found to significantly affect the resulting calibrations (as parameterized by root mean square error of cross validation). Physically heterogeneous AMF samples held at 20 °C were shown to allow reliable SFC predictions on the basis of collected Raman spectra. In contrast to SFC calibrations, physically homogenous samples in a liquid form were ideal for TG class concentration predictions, however, not all TG classes could be reliably predicted.

The condensation of a dipyrromethane with ferrocene aldehyde leads to a single atropisomer of α,α-5,15-bis(ferrocenyl)-2,8,12,18-tetrabutyl-3,7,13,17-tetramethylporphyrin 1; electrochemistry of 1 and Ni-1 reveals two consecutive ferrocene-based one-electron oxidation waves, which are separated by 0.19 and 0.41 V, respectively.

A variety of new bis(oligo(oxyethylene)styryl)sexithiophenes have been prepared by chemical oxidation of ether-substituted styrylterthiophenes with FeCl3. In all cases dimers are formed in high yields, rather than the expected polymers. In addition, although three different regioisomers can potentially be formed from such an oxidation, the isolable products are shown to consist of only the head-to-head regioisomer. Theoretical calculations on alkoxystyrylterthiophenes show that this can be understood in terms of an uneven electron spin density distribution at the two alpha-positions available for polymerization. Electron density calculations on the resulting head-to-head alkoxystyrylsexithiophenes show that the spin density is concentrated in the core of the molecule rather than at the alpha-positions, a result that explains the absence of significant amounts of higher oligomers.

A number of mono- and bi-nuclear rhenium(I) complexes have been prepared and their physical properties, including the infrared spectra of the reduced complexes, have been studied. These compounds have the general formula [Re(CO)3Cl(L)] and [Cl(CO)3Re(μ-L)Re(CO)3Cl], where L can be 2,3-(2′,2″)-diquinolylquinoxaline, 6,7-dimethyl-2,3-(2′,2″)-diquinolylquinoxaline, 2,3-(2′,2″)-diquinolylbenzoquinoxaline, 6,7-dichloro-2,3-(2′,2″)-diquinolylquinoxaline, 2,3-(2′,2″)-diquinoxalylquinoxaline, 6,7-dimethyl-2,3-(2′,2″)-diquinoxalylquinoxaline, 2,3-(2′,2″)-diquinoxalylbenzoquinoxaline and 6,7-dichloro-2,3-(2′,2″)-diquinoxalylquinoxaline. The electrochemical studies show that the first reduction potential of the free ligands correlates with the reductions of the corresponding mono- and bi-nuclear complexes. The properties of the complexes have been modelled using semi-empirical methods. These show linear correlations between: (a) the energy of the MLCT transitions versus the difference in energy between the LUMO and the HOMO and (b) the change in carbonyl force constant with reduction vs. the wavefunction amplitude of the π* LUMO at the site of coordination. The experimental data and calculations point to significant alterations in the π* LUMO with substitution at the ligand and with the chelation of a second Re(I) center.

Raman spectroelectrochemical and X-ray crystallographic studies have been made for the binuclear copper(I) complex, [(Ph3P)2Cu(dpq)Cu(PPh3)2][BF4]2, where dpq is the bridging ligand 2,3-di(2-pyridyl)quinoxaline. The X-ray data show that the pyridine rings are twisted out of plane with respect to the quinoxaline ring which is itself non-planar. The UV/VIS spectra of the metal-to-ligand charge-transfer excited state and those of the electrochemically reduced complex are similar. The resonance-Raman spectrum of the latter species exhibits little change in the frequency of the pyridinylquinoxaline inter-ring C–C bond stretching mode, compared to the ground elecronic state. This suggests minimum change in the inter-ring C–C bond order in the electrochemically or charge-transfer generated radical anion. Semiempirical molecular-orbital calculations on both the neutral dpq and radical anion show two near-degenerate lowest unoccupied orbitals in the neutral species. One is strongly bonding across the inter-ring C–C bond while the other is almost non-bonding. The Raman data suggest that it is this latter orbital which is populated in the transient and electrochemical experiments.