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Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in the electronic circular dichroism. The fast dimerisation event leads to a >500 mV shift of the oxidation potential, affording a large area of bistability, where the chiroptical signal only depends on the redox history.

A series of diketopyrrolopyrrole (DPP) dyes with a terminal phosphonic acid group for attachment to metal oxide surfaces were synthesised and the effect of side chain modification on their properties investigated. The organic photosensitisers feature strong visible light absorption (λ = 400 to 575 nm) and electrochemical and fluorescence studies revealed that the excited state of all dyes provides sufficient driving force for electron injection into the TiO2 conduction band. The performance of the DPP chromophores attached to TiO2 nanoparticles for photocatalytic H2 evolution with co-immobilised molecular Co and Ni catalysts was subsequently studied, resulting in solar fuel generation with a dye-sensitised semiconductor nanoparticle system suspended in water without precious metal components. The performance of the DPP dyes in photocatalysis did not only depend on electronic parameters, but also on properties of the side chain such as polarity, steric hinderance and hydrophobicity as well as the specific experimental conditions and the nature of the sacrificial electron donor. In an aqueous pH 4.5 ascorbic acid solution with a phosphonated DuBois-type Ni catalyst, a DPP-based turnover number (TONDPP) of up to 205 was obtained during UV-free simulated solar light irradiation (100 mW cm−2, AM 1.5G, λ > 420 nm) after 1 day. DPP-sensitised TiO2 nanoparticles were also successfully used in combination with a hydrogenase or platinum instead of the synthetic H2 evolution catalysts and the platinum-based system achieved a TONDPP of up to 2660, which significantly outperforms an analogous system using a phosphonated Ru tris(bipyridine) dye (TONRu = 431). Finally, transient absorption spectroscopy was performed to study interfacial recombination and dye regeneration kinetics revealing that the different performances of the DPP dyes are most likely dictated by the different regeneration efficiencies of the oxidised chromophores.

Four novel π-conjugated chromophores with an azobenzene core (1-4) have been synthesized exploiting Pd-catalysed cross-coupling reactions between ethynyl-bearing azobenzene cores and suitably-designed peripheral groups. While in molecules 2 and 3 the azobenzene core is equipped, respectively, with ethynyl and 1,3-butadiyne spacers terminated with a substituted aniline, molecule 4 is an homologue of derivative 2 in which the terminal moieties are replaced by meso-substituted Zn-porphyrins. X-Ray crystallographic studies of substituted azobenzene 2 reveal a nearly planar arrangement of the four phenyl rings and the trans configuration of the NN central unit. The UV-Vis absorption spectrum of molecule 1 in cyclohexane (CHX) is very similar to that of unsubstituted azobenzenes; upon irradiation at the maximum of the intense π-π absorption feature (360 nm), 1 undergoes trans → cis photoisomerization reaching a photostationary state. The process is fully reversible both photochemically and thermally (ca. 120 min in the dark). The UV-Vis electronic absorption features of 2-4 are dramatically different compared to those of 1, but the photochemical process can still be traced and exhibits full reversibility in CHX. Also in the case of compound 4, where the photoreactive azobenzene excited states might be quenched by the low-lying porphyrin electronic levels, the photoreaction does occur. Extensive STM investigations of self-assembled monolayers (SAMs) of 2 and 3 at the solid/liquid interface were performed by means of scanning tunneling microscopy (STM) on highly oriented pyrolytic graphite (HOPG). It is evidenced that only the trans isomer can be physisorbed on the surface whereas the cis form, either produced under illumination in situ or prepared by irradiation of the solution prior to deposition (ex-situ), is never observed on the surface. The smallest azobenzene 1 and the bisporphyrin system 4 did not physisorb onto the surface because of the very small size and the bulky 3,5-di(tert-butyl) phenyl groups hindering flat adsorption on HOPG, respectively. © 2009 The Royal Society of Chemistry.

A numerical method is presented to estimate the influence of a nearby substrate on the polarization energy and outer sphere reorganization energy (λo) for intermolecular hole transfer for a series of dye molecules. The calculation considers the net charge distribution of the oxidised molecule (determined from quantum chemical calculation of the highest occupied molecular orbital of the neutral molecule within the frozen orbital approximation) encapsulated within a conformal cavity, by the molecules total electron density. An analytical point charge approximation was used at longer range. The molecular cavity was either surrounded by a single polarizable continuum, or, to simulate a nearby substrate, embedded at different positions relative to the interface between two semi-infinite slabs with different dielectric constants. The calculated λo values in the single dielectric medium were linearly related to the outer-sphere reorganisation energy calculated from DFT with a polarizable continuum model, validating the approach. In the two phase system, variations in λo was sensitive to the position of the substrate relative to the molecule and differences in the Pekar factor (1/εo - 1/εr) for the media. For dye molecules in ACN positioned touching a TiO2 substrate λo was typically about 20% lower than in pure ACN depending on the molecular configuration. Our approach can be adapted to systems of more than two media.

Unwanted photoinduced responses are well-known adverse effects of most promazine drugs, including levomepromazine (LPZ, Levoprome((R)) or Nozinan((R))). This drug is indicated in psychiatry primarily for the treatment of schizophrenia and other schizoaffective disorders. Levomepromazine's particular sedative properties make it especially fit for use in psychiatric intensive care. Nevertheless, it is photolabile under UV-A and UV-B light in aerobic conditions resulting in the formation of its sulfoxide. The LPZ photochemistry in acetonitrile (MeCN) is completely different from that in methanol (MeOH) and phosphate buffer solutions (PBS, pH = 7.4). The major photoproduct in PBS and MeOH under aerobic conditions is levomepromazine sulfoxide (LPZSO), although the amount is considerably higher in the aqueous environment. The corresponding main photoproduct in MeCN could not be characterized. The destruction quantum yields of LPZ in PBS, MeOH and MeCN are 0.13, 0.02 and, This work has been supported in part by NIH-MBRS grant SO6GM08216 to UPR-Humacao and the UPRH-FOPI Program (CGR). Financial support by the Spanish Government (Ramon y Cajal contract to VLV) is gratefully acknowledged. We especially thank the High Performance Computing Facility at UPR Rio Piedras for assistance with the theoretical calculations and Elizabeth Hodges for the revision of the manuscript.

The one-pot double Diels-Alder reactions of 3,4-di(methylene)tetrahydrothiophene-1,1-dioxide using temperature as the only chemocontrol element are described. Zn-dust promoted the 1,4-debromination of 3,4-bis(bromomethyl)-2,5-dihydrothiophene-1,1-dioxide in 5-nonanone, under MW conditions, followed by a Diels-Alder reaction, an SO2 extrusion step and a second Diels-Alder reaction. This approach was applied successfully in double [4 + 2] cycloadditions using the same or two different dienophiles to afford the corresponding Diels-Alder products in excellent yields. An elegant and practical method for [4 + 2] functionalisation/[4 + 2] derivatization of C-60 was achieved in a one-pot manner via the formation of a new reactive C-66 dienic intermediate. Rsc Advances

[EN] The influence of ring size on the photobehaviour of condensed 1,4-naphthoquinone systems, such as pyrano-and furano-derivatives (1 and 2, respectively) has been investigated. The absorption spectra for both families of naphthoquinones reveal clear differences; in the case of 2 they extend to longer wavelengths. A solvatochromic red shift in polar solvents is consistent with the pi,pi* character of the S-0 -> S-1 electronic transition in all cases. Theoretical (B3LYP) analysis of the HOMO and LUMO Kohn-Sham molecular orbitals of the S-0 state indicates that they are pi and pi* in nature, consistent with the experimental observation. A systematic study on the efficiency of singlet oxygen generation by these 1,4-naphthoquinones is presented, and values larger than 0.7 were found in every case. In accordance with these results, laser flash photolysis of deoxygenated acetonitrile solutions led to the formation of detectable triplet transient species with absorptions at 390 and 450 nm (1) and at 370 nm (2), with phi(ISC) close to 1. Additionally, the calculated energies for the T-1 states relative to the S-0 states at UB3LYP/6-311++G** are ca. 47 kcal mol(-1) for 1 and 43 kcal mol(-1) for 2. A comparison of the geometrical parameters for the S-0 and T-1 states reveals a marked difference with respect to the arrangement of the exocyclic phenyl ring whilst a comparison of electronic parameters revealed the change from a quinone structure to a di-dehydroquinone diradical structure., This research was supported by Spanish Government MICINN (CTQ2009-13699 and PHB2008-0104-PC) and by the Brazilian agencies: CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior), CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico), FAPERJ (Fundacao de Amparo a pesquisa do Estado do Rio de Janeiro) and FAPERJ-PRONEX grant number 110.574/2010.

peer-reviewed The range of salts used as supporting electrolytes in electrochemical studies of redox proteins and enzymes varies widely, with the choice of an electrolyte relying on the assumption that the electrolyte used does not affect the electrochemical properties of the proteins and enzymes under investigation. Examination of the electrochemical properties of the redox protein cytochrome c (cyt c) at a 4,4'-bipyridyl modified gold electrode demonstrates that both the redox potential (E-o') and the faradaic current are influenced by the nature of the electrolyte used, in a manner explained primarily by Hofmeister effects. The faradaic peak currents display an atypical trend on switching from kosmotropic to chaotropic anions, with a maximum current observed in the presence of Cl-. For a series of cations, the peak current increased in the sequence: Li+ (0.34 mu A) Br- (0.35 mu A) > ClO4- (0.35 mu A) > SCN- (0.31 mu A) > F- (0.30 mu A). E-o' decreased by a total of 24 mV across the series F- > Cl- > Br- > ClO4- > SCN- whereas no specific ion effect on E-o' was observed for cations. Factorisation of E-o' into its enthalpic and entropic components showed that while no specific trends were observed, large changes in Delta H-o' and Delta S-o' occurred with individual ions. The effect of anions on the faradaic peak current can be qualitatively explained by considering Collins' empirical rule of 'matching water affinities'. The effect of cations cannot be explained by this rule. However, both anion and cation effects can be understood by taking into account the cooperative action of electrostatic and ion dispersion forces. The results demonstrate that the choice of a supporting electrolyte in electrochemical investigations of redox proteins is important and emphasize that care needs to be taken in the determination and comparison of E-o', Delta H-o' and Delta S-o' in different solutions. ACCEPTED peer-reviewed

Triplet-mediated pyrimidine (Pyr) dimerisation is a key process in photochemical damage to DNA. It may occur in the presence of a photosensitiser, provided that a number of requirements are fulfilled, such as favourable intersystem crossing quantum yield and high triplet energy. The attention has been mainly focused on cyclobutane pyrimidine dimers, as they are by far the most relevant Pyr photoproducts obtained by sensitisation. The present perspective deals with the involved chemistry, not only in DNA but also in its simple building blocks. It also includes the photophysical characterisation of the Pyr triplet excited states, as well as a brief discussion of the theoretical aspects., Financial support from the Spanish Government (CTQ2009-13699, CTQ2009-14196, JAE Doc fellowship for M. C. C. and Ramon y Cajal contract for V. L.-V.) and EU (CM0603) is gratefully acknowledged.

The tetraruthenium polyoxometalate water oxidation catalyst 1 performs very fast hole scavenging from photogenerated Ru(III) polypyridine complexes, both in homogeneous solution and at a sensitized nanocrystalline TiO(2) surface.

The catalytic effect of tetraphenylporphyrin on the oxygen reduction with ferrocene in 1,2-dichloroethane can be finely tuned by varying the molar ratio of the acid to the catalyst present in the solution. The mechanism involves binding of molecular oxygen to the protonated free porphyrin base, in competition with ion pairing between the protonated base and the acid anion present.