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The synthesis, spectroelectrochemical and structural characteristics of highly electron-accepting diketopyrrrolopyrrole (DPP) molecules with adjoining pyridinium rings is reported, along with an assessment of their toxicity, which is apparently low. The compounds show reversible electrochemistry and in one subfamily a massive increase in molar extinction coefficient upon electrochemical reduction. [ABSTRACT FROM AUTHOR]

Donor-acceptor dyads and triads comprising core-substituted naphthalene diimide (NDI) chromophores and either phenothiazine or phenoxazine donors are described. Synthesis combined with electrochemical and spectroelectrochemical investigations facilitates characterisation of the various redox states of these molecules, confirming the ability to combine arrays of electron donating and accepting moieties into single species that retain the redox properties of these individual moieties. [ABSTRACT FROM AUTHOR]

A mixed‐addenda W/Mo hybrid polyoxometalate cluster – K6[P2W15Mo2O61(POC6H5)2] (1) was synthesised from the condensation of K10[P2W15Mo2O61] and PO3C6H7 under acidic conditions. Single‐crystal X‐ray diffraction confirmed the structure of the hybrid cluster and the presence of two Mo centres in the cap of the lacunary cluster. The electronic effects of metal substitution were studied by cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. Comparing 1 to its tungsten‐only analogue K6[P2W17O61(POC6H5)2] (2), a more positive potential for the first reduction process was induced by the substitution of W for Mo, consistent with a significant lowering of the cluster LUMO energy. [ABSTRACT FROM AUTHOR]

A series of symmetrically bis‐4‐methoxybenzyl (4MB) N‐substituted 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP) derivatives have been synthesized. The 4MB unit makes the DPP core soluble, and shows subtle modification of up to 0.2 eV in ground and excited states of the core when compared with related alkyl derivatives. Absorption and emission spectroscopy, as well as electrochemical and computational methods have been employed to prove the importance of the peripheral aryl units on the donor/ acceptor properties of the molecules. The 4MB products are highly fluorescent (quantum yields approaching 100 % in solution), with a unique distribution of frontier states shown by spectroelectrochemistry. The solid‐state fluorescence correlates with the X‐ray crystal structures of the compounds, a Stokes shift of approximately 80 nm is seen for two of the compounds. The frontier energy levels show that this subtle substitutional change could be of future use in molecular energy level tailoring in these, and related, materials for organic (opto)electronics. [ABSTRACT FROM AUTHOR]

Electron-transfer processes play a significant role in host-guest interactions and determine physicochemical phenomena emerging at the nanoscale that can be harnessed in electronic or optical devices, as well as biochemical and catalytic systems. A novel method for qualifying and quantifying the electronic doping of single walled carbon nanotubes (SWNTs) using electrochemistry has been developed that establishes a direct link between these experimental measurements and ab initio DFT calculations. Metallocenes such as cobaltocene and methylated ferrocene derivatives were encapsulated inside SWNTs (1.4 nm diameter) and cyclic voltammetry (CV) was performed on the resultant host-guest systems. The electron transfer between the guest molecules and the host SWNTs is measured as a function of shift in the redox potential ( E1/2) of CoII/CoI, CoIII/CoII and FeIII/FeII. Furthermore, the shift in E1/2 is inversely proportional to the nanotube diameter. To quantify the amount of electron transfer from the guest molecules to the SWNTs, a novel method using coulometry was developed, allowing the mapping of the density of states and the Fermi level of the SWNTs. Correlated with theoretical calculations, coulometry provides an accurate indication of n/p-doping of the SWNTs. [ABSTRACT FROM AUTHOR]

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. This excited state is quenched by oxygen, leading to the formation of singlet oxygen in dichloromethane, recorded by time-resolved near-infrared luminescence measurements. [ABSTRACT FROM AUTHOR]

Abstract: New CuII and NiII complexes of potentially tridentate N2O Schiff base ligands 1 and 2 have been synthesised and characterised. [Cu(2)(OH2)]+ possesses a square planar geometry in the solid state whereas [Ni(1)2] possesses a distorted octahedral geometry in which the amine donors of 1 coordinate weakly to the NiII centre. EPR spectroscopy demonstrates that the N2O2 coordination sphere of [Cu(2)(OH2)]+ is retained in CH2Cl2 solution. [Cu(2)(OH2)]+ exhibits a reversible one electron oxidation at E 1/2 =0.54V versus [Fc]+/[Fc], the product of which has been characterised by UV–Vis absorption and EPR spectroscopies. The spectroscopic signature of the oxidised product is consistent with the formation of a stable phenoxyl radical ligand bound to a CuII centre. [Ni(1)2] possesses a reversible metal-based oxidation process at E 1/2 =0.03V versus [Fc]+/[Fc] and a further oxidation, attributed to the generation of a phenoxyl radical centre, at =0.44V versus [Fc]+/[Fc]. UV–Vis absorption and EPR spectroscopic studies indicate that the lower potential process is a formal NiIII/II couple. In contrast, the pro-ligands 1H and 2H exhibit chemically irreversible oxidation processes at =0.42 and 0.40V versus Fc+/Fc, respectively, and do not support the formation of stable phenoxyl radical species. [Copyright &y& Elsevier]

The electronic effects of varying the nature of the carbonyl groups in a series of perylene-3,4,9,10-tetracarbonyl compounds have been investigated. The four carbonyl groups comprise of esters, imides and anhydrides and combinations thereof. The series has been extensively characterised by electrochemical methods and it is found that the combination of imide and anhydride groups enhances the electron accepting properties of the perylene core. In contrast, the perylene core is the most electron rich when each of the four peri -positions is functionalised with an ester group. In the case of tetra-esterified perylene a reversible oxidation process can also be observed. The nature of the carbonyl species provides a degree of redox potential tunability whilst maintaining similar optical properties of the chromophores. This suggests that careful selection of peri -substituents is important in the fabrication of optoelectronic devices incorporating 3,4,9,10-tetracarbonyl perylene species. Image 1 • Varying perylene-3,4,9,10-tetracarbonyl species affects their electron accepting ability. • Perylenes derivatised with combinations of with esters, imides and anhydrides are studied. • The nature of the carbonyl species provides a degree of redox potential tunability. • Spectroelectrochemical measurements determine the optical properties of the chromophores. [ABSTRACT FROM AUTHOR]

1,4-dimethoxypillar[5]arene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in [2]rotaxanes, suggesting that pillar[5]arenes can be employed as viable, yet unreported, electron donors. [ABSTRACT FROM AUTHOR]

The article presents a study which uses magnetic circular dichroism (MCD) spectroscopy to examine the magnetic properties of three interconvertible redox states of a single-molecule magnet (SMM). It explores the spectroelectrochemical characteristics of anionic, neutral, and cationic equivalents of a terbium double-decker complex under frozen dilute solutions at low temperature. Results demonstrate the effectiveness of MCD technique in understanding the magnetization properties of SSM compound.

A general route for synthesis of six structurally similar Pt(II) diimine thiolate/phenolates chromophores possessing bulky phenolate or thiolate ligands is reported. The Pt chromophores were characterized using an array of techniques including ¹H, 13C, and 195Pt NMR, absorption, emission, (spectro)electrochemistry, and EPR spectroscopy. Systematic variation of the electronic structure of the Pt(II) chromophores studied was achieved by (i) changing solvent polarity; (ii) substituting oxygen for sulfur in the donor ligand; (iii) alternating donor ligands from bis- to di-coordination; and (iv) changing the electron donating/withdrawing properties of the ligand(s). The lowest excited state in these new chromophores was assigned to a [charge-transfer-to-diimine] transition from the HOMO of mixed Pt/S (or Pt/O) character on the basis of absorption and emission spectroscopy, UV/vis (spectro)electrochemistry, and EPR spectroscopy. One of the chromophores, Pt(dpphen)(3,5-di-tert-butyl-catecholate) represents an example of a Pt-(II) diimine phenolate chromophore that possesses a reversible oxidation centered predominantly on the donor ligand. Results from EPR spectroscopy indicate participation of the Pt(II) orbitals in the HOMO. There is a dramatic difference in the photophysical properties of carborane complexes compared to other mixed-ligand Pt(II) compounds, which includes room-temperature emission and photostability. The charge-transfer character of the lowest excited state in this series of chromophores is maintained throughout. Moreover, the absorption and emission energies and the redox properties of the excited state can be significantly tuned. [ABSTRACT FROM AUTHOR]

Graphical abstract [Re(CO) 3 Cl(NN)] complexes have been functionalised with pendent pyridyl groups, designed for photocatalytic CO 2 binding and reduction. The complexes are investigated using time-resolved infrared spectroscopy in a series of solvents to unravel their interesting photopysical properties, with solvent dependant 3MLCT(phen), 3MLCT(phz) and 3IL ππ* excited states observed. In addition, the one electron reduced complexes are characterised using FTIR, UV/Visible and EPR spectroscopies which reveals a 'phz' localised electron with the potential to act as a CO 2 reducing agent. Abstract We report the synthesis, electrochemical, and photophysical properties of a series of rhenium complexes, [Re(CO) 3 Cl(NN)] (NN = dppp2, dppp3, and dppp2Br; dppp2 = pyrido[2′,3′:5,6]pyrazino[2,3- f ][1,10]phenanthroline, dppp3 = pyrido[3′,4′:5,6]pyrazino[2,3-f][1,10]phenanthroline, dppp2Br = 8-bromopyrido[2′,3′:5,6]pyrazino[2,3- f ][1,10]phenanthroline), which have potential for use as CO 2 photoreduction catalysts. The complexes are related to [Re(CO) 3 Cl(dppz)] (dppz = dipyrido[3,2- a :2′,3′- c ]phenazine) but have an additional nitrogen heteroatom in the distal phenazine (phz) aromatic ring of the dppz ligand which is known to promote potential photoinduced CO 2 binding and reduction in related complexes. We use Fourier transform infrared (FTIR), UV/Visible, electron paramagnetic resonance (EPR) and time-resolved infrared (TRIR) spectroscopies to investigate how the location of the additional nitrogen atom, and how the nature of the substituents affects the photophysical properties. In addition, the one electron reduced catalysts are generated following bulk electrochemical reduction and characterised in CH 2 Cl 2. TRIR experiments in d 6 -DMSO, CH 3 CN, CH 2 Cl 2 , THF and toluene reveal that excitation generates a 3MLCT(phz) (phz = phenazine) excited state in all compounds. In CH 3 CN and d 6 -DMSO (not for [Re(CO) 3 Cl(dppp2)]), we observe the concomitant formation of an 3IL ππ* (IL = intra ligand) excited state. For [Re(CO) 3 Cl(dppp2)] and [Re(CO) 3 Cl(dppp3)] in toluene, a mixture of 3MLCT(phen) (phen = phenanthroline) and 3MLCT(phz) states appear to form together, and decay at the same rate. Inclusion of an nitrogen atom in the phz moiety of the dppz ligand lowers the 'phz' localised lowest unoccupied molecular orbital (LUMO) energy potentially favouring population of the 3MLCT(phz) state. This effect is more pronounced for [Re(CO) 3 Cl(dppp3)] with a more positive reduction potential (E ½ = −1.16 vs Fc+/Fc in CH 2 Cl 2) compared to [Re(CO) 3 Cl(dppp2)] (E ½ = −1.20 V vs Fc+/Fc in CH 2 Cl 2). For [Re(CO) 3 Cl(dppp2Br)], lowering of the LUMO energy results in an even more positive potential (E ½ = −1.10 vs Fc+/Fc in CH 2 Cl 2) and this can be seen to affect the photophysics. We find the excited state lifetime for each complex increases with decreasing dielectric constant, where their lifetime in toluene is greater than 100 times longer than that observed in d 6 -DMSO. [ABSTRACT FROM AUTHOR]

F64Pc2Ln (1Ln, Ln = Tb or Lu) represent the first halogenated phthalocyanine double-decker lanthanide complexes, and 1Tb exhibits single-molecule magnet properties as revealed by solid-state magnetometry. The fluorine substituents of the phthalocyanine rings have a dramatic effect on the redox properties of the F64Pc2Ln complexes, namely, a stabilization of their reduced states. Electrochemical and spectroelectrochemical measurements demonstrate that the 1Tb-/2- and 1Tb2-/3- couples exhibit redox reversibility and that the 1Tb-, 1Tb2- and 1Tb3- species may be prepared by bulk electrolysis in acetone. Low-temperature MCD studies reveal for the first time magnetization hystereses for the super-reduced dianionic and trianionic states of Pc2Ln. [ABSTRACT FROM AUTHOR]