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The origin of energetic disorder in organic semiconductors and its impact on opto-electronic properties remains a topic of intense controversy. Particularly the disorder at electron donor-acceptor interfaces for organic photovoltaics is pivotal to understand as it is expected to affect photo-carrier generation, recombination and consequently device efficiency parameters. In this work we evaluate the temperature dependence of the line-shape of the photoluminescence (PL) and electroluminescence (EL) spectra of small molecule:fullerene blend devices, with the ambition to disentangle dynamic and static disorder contributions. The EL emission spectra are dominated by charge-transfer (CT) state emission and are confirmed to be of Gaussian character and almost completely voltage independent. More importantly, a strong line-width narrowing is persistently observed upon cooling, down to a certain material specific low temperature, below which the line-width remains constant. It is consequently clear that the main portion of the line-width measured at operating conditions of room temperature or higher, is originating from thermally activated, or dynamic, disorder. The observed temperature dependence of the high-energy emission tail can be fully described by taking into account high and low frequency molecular vibrational modes, without having to rely on static disorder. The presence of low frequency molecular modes with large Huang-Rhys factors results in a Gaussian line-shape, which is additionally broadened at high temperature by thermal population of high frequency intra-molecular modes. We therefore cast strong doubts regarding the commonly used assumption that single temperature optical measurements of absorption or emission tails are able to provide meaningful information regarding the shape of a static density of states tail. K. T. acknowledges the German Research Foundation (DFG) through project 382633022 (RECOLPER) and the Experimental Physics VI chair of Prof. Vladimir Dyakonov at Wurzburg University. J. B. acknowledges the DFG project VA 1035/5-1 (Photogen) and the Sachsische Aufbaubank through project no. 100325708 (Infrakart). The authors also acknowledge discussion on the topic with Robert Street, Thomas Kirchartz, Frank Ortmann and Carsten Deibel. Tvingstedt, K (corresponding author), Julius Maximilian Univ Wurzburg, Expt Phys 6, D-97074 Wurzburg, Germany. ktvingstedt@physik.uni-wuerzburg.de

Optical pump-probe spectroscopy is a crucial tool to investigate the excited state behaviour of materials and is especially useful to investigate the photoexcitation dynamics of bulk heterojunctions as found in organic solar cells. Most common techniques for such investigations involve pulses with an energy density in the range of several tens of J cm(-2), emitted with kHz repetition rate. Such pulse energy can entail non-linear processes due to the formation of high carrier concentrations and can furthermore severely damage the sample material. Here we introduce a softer approach with pulses of nJ cm(-2) energy density and a photon flux which is more than three orders of magnitude lower than in regular techniques. We show the capability of our low-cost and easy to make set-up by investigating two prototypical donor-acceptor polymers, C-PCPDTBT and its silicon variant Si-PCPDTBT. Given the high pulse repetition rate in the MHz regime, we are readily able to monitor sample changes of 10(-5) and find exciton lifetimes of 108 and 150 ps for C- and Si-PCPDTBT respectively.

A mononuclear hexa-coordinated iron carbonyl complex [Fe(mu-bdt)(CO)(2)(PTA)(2)](1) (bdt = 1,2-benzenedithiolate; PTA = 1,3,5-triaza-7-phosphaadamantane) with two bulky phosphine ligands in the trans position was synthesized and characterized by X-ray structural analysis coulometry data, FTIR, electrochemistry and electronic structure calculations. The complex undergoes a facilitated two-electron reduction 1/1(2-) and shows an inverted one-electron reduction for 1/1(-) at higher potentials. Electrochemical investigations of 1 are compared to the closely related [Fe(bdt)(CO)(2)(PMe3)(2)] compound. A mechanistic suggestion for the hydrogen evolution reaction upon proton reduction from acid media is derived. The stability of 1 in both weak and strong acids is monitored by cyclic voltammetry.

In this paper, we investigate the synthetic tailoring of the spectral response and intramolecular charge transfer (ICT) of beta-enaminones through bandgap modulation. Two donor/acceptor substituted beta-enaminones, namely, 3-(4-methoxyphenylamino)-2-cyclohexen-1-one (OACO) and 3-(4nitrophenylamino)- 2-cyclohexen-1-one (NACO) have been synthesized along with their unsubstituted counterpart, 3-(phenylamino)-2-cyclohexen-1-one (PACO). Steady state as well as time resolved spectroscopic techniques with picosecond resolution are used to record their spectral responses. Substitution of the donor group (-OCH3) mildly enhances the charge transfer from the phenyl ring to the enaminone moiety, while substitution of the acceptor group (-NO2) jeopardizes the charge transfer through mutual electron withdrawing effects of PNA and enaminone moieties. Combined experimental and quantum chemical investigations reveal that the ground state photophysics of OACO and NACO in water are controlled by both microscopic and macroscopic solvation with dominant contribution from the former. Time dependent density functional theory (TDDFT) calculations predict that the HOMO to [LUMO+1] transition gives rise to the absorption spectra of OACO in water, while the absorption by the enaminone moiety of NACO arises as a result of a HOMO to LUMO transition. A crossing between the first (S-1) and the second excited (S-2) states takes place in the microclusters of PACO, OACO and NACO with water. The intersystem crossing (ISC) has been found to be the major reason for low quantum yields in these molecules. The band gap modulation through waxing and waning of the conjugation strength is expected to throw light on many ICT-driven processes and provides means of tuning the properties depending on it.

The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core–shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady state absorption study suggests the exciton delocalization from CdSe QDs in the presence of the thiols. However similar features were not observed in the presence of a ZnS shell over a CdSe core, instead a broadening in the excitonic peak was observed with both APT and ADPT but not with AAT. This exciton delocalization and broadening in the excitonic peak was also confirmed by ultrafast transient absorption studies. Steady state and time resolved emission studies show hole transfer from photo-excited QDs and CSQDs to the thiols. A signature of hot hole extraction was observed in transient absorption studies which was confirmed by fluorescence upconversion studies. Both hot and thermalized hole transfer rates from CdSe QDs and CdSe/ZnS CSQDs to the thiols were determined using the fluorescence up-conversion technique. Experiments with different ZnS shell thicknesses have been carried out which suggest that hole transfer is possible till 2.5 monolayer of the ZnS shell. To the best of our knowledge we are reporting for the first time the extraction of hot holes from CdSe/ZnS type I CSQDs by a molecular adsorbate.

The spectroscopic characterisation of a series of [Ru(LL)(CN)(4)](2-) complexes, where LL = 1,10-phenanthroline (phen) and its methyl- and phenyl-substituted derivatives and several deuteriated isotopologues are reported. The optical and vibrational properties of these complexes are compared with that of the series of 2,2'-bipyridine (bipy) derivatives and analogous [Ru(LL)(3)](2+) complexes. It has been demonstrated that substitution at the 4,4' positions of bipy and 4,7-positions of phen by electron donating (CH3) and withdrawing (C6H5, COO-) groups induces a pronounced blue and red shift, respectively, in the lowest energy (MLCT)-M-1 absorption band of [Ru(LL)(CN)(4)](2-). The energy of the emission originating from the (MLCT)-M-3 excited state is found to be dependant on the nature of the vibrational modes of the aromatic rings and the electron donating and/or withdrawing properties of the substituents. Single-mode Franck-Condon analysis indicates that methyl substitution leads to a significant increase in the Huang-Rhys factor (S-M), while phenyl substitution results in a decrease in S-M for both series (bipy and phen) of complexes. The rate of non-radiative (k(nr)) and radiative decay (k(ph)) to the ground state and the parameters of thermally activated deactivation pathways (A(4th), Delta E-4th and A(dd), Delta E-dd) were estimated from the temperature dependence of luminescence quantum yields and lifetimes. It has been demonstrated that the non-radiative decay rate and the temperature dependent decay processes are more efficient for bipy complexes than for phen derivatives due to the rigidity of the latter ligand.

The X-ray crystal structure of the N2 isomers of the Ru(bipy)2 complexes of Hphpztr (1) and Hpztr (2), (bipy = 2,2'-bipyridine, Hphpztr = 2-(5'-phenyl-4'H-[1,2,4]triazol-3'-yl)pyrazine and Hpztr = 2-(4'H-[1,2,4]triazol-3'-yl)pyrazine) are reported. The molecular structure obtained for 2 demonstrates an interesting structural aspect in the sharing of a single proton between two molecular units. The isolation of the Δ and Λ stereoisomers of 1 and [Ru(phen)2(pztr)]+ (phen = 1,10-phenanthroline) (3) by semipreparative HPLC is also reported. The compounds obtained are characterised by electronic spectroscopy and particular attention is paid to the photophysical properties of Δ and Λ isomers of 1 and 3, in chiral enantiopure and racemic solvents.

The synthesis, purification and characterisation of two coordination isomers of ruthenium(II) and osmium (II) complexes containing the ligand 3-(pyrazin-2'-yl)-5-(pyridin-2"-yl)-1,2,4-triazole (Hppt) are described. The X-ray and molecular structure of the complex [Ru(bipy)(2) (ppt)] PF6.CH3OH (1a) is reported, where the Ru( bipy)(2)-centre is bound to the ppt(-) ligand via the pyridine nitrogen and the N1 atom of the triazole ring. H-1 NMR spectroscopic measurements confirm that in the second isomer (1b) the Ru( bipy)(2)-moiety is bound via the N2 atom of the triazole ring and the pyrazine ring. Partially deuteriated metal complexes are utilised to facilitate interpretation of H-1 NMR spectra. The redox and electronic properties indicate that there are significant differences in the electronic properties of the two coordination isomers obtained. The acid-base properties of the compounds are also reported and show that the pK(a) of the 1,2,4-triazole ring varies systematically depending on the nature of the non-coordinating substituent. Analysis of these data indicates a significant electronic interaction between the pyridyl/pyrazyl rings and the 1,2,4-triazole ring in the coordinated ppt(-) ligand.

Bisamino(diphosphonite), p-C6H4{N{P(OC6H4C3H5-o)(2)}(2)}(2) (1), was prepared by reacting p-C6H4{N(PCl2)(2)}(2) with four equivalents of o-allylphenol in 85% yield. Compound 1 on treatment with [M(CO)(4)(HNC5H10)(2)] (M = Mo or W) gave cis-[{M(CO)(4)}(2){p-C6H4{N(P(OC6H4C3H5-o)(2))(2)}(2)}] (2, M = Mo; 3, M = W). The reaction of 1 with [Fe(eta(5)-C5H5)(CO)(2)](2) yielded the complex [{Fe(eta(5)-C5H5)(mu-CO)}(2){p-C6H4{N(P-(OC6H4C3H5-o)(2))(2)}(2)}] (4). Treatment of 1 with Fe(CO)(5) furnished a mononuclear complex, [{Fe(CO)(3)}(2)-{p-C6H4{N{P(OC6H4C3H5-o)(2)}(2)}(2)}] (5). The ruthenium(II) complex, [{(eta(6)-p-cymene)Ru(mu-Cl)(3)RuCl}(2){p-C6H4-{N(P(OC6H4C3H5-o)(2))(2)}(2)}] (6), was obtained on treatment of ligand 1 with [(eta(6)-p-cymene)Ru(Cl)(2)](2). The reaction between 1 and [Rh(COD) Cl](2) (COD = 1,5-cyclooctadiene) in dichloromethane resulted in the formation of a dinuclear complex [{RhCl}(2){p-C6H4{N(P(OC6H4C3H5-o)(2))(2)}(2)}] (7), in which the allyl double bond of one of the phenoxy groups coordinates to the metal center. When ligand 1 was reacted with two equivalents of [Pd(COD)Cl-2], a dinuclear complex [{PdCl2}(2)-{p-C6H4{N(P(OC6H4C3H5-o)(2))(2)}(2)}] (8) was obtained. With copper(I) halides, ligand 1 afforded tetranuclear complexes, [{(Cu(mu-X)(NCCH3))(2)}(2)-{p-C6H4{N(P(OC6H4C3H5-o)(2))(2)}(2)}] (9, X = Cl; 10, X = Br; 11, X = I). Reaction of 1 with four equivalents of [AuCl(SMe2)] produced a tetranuclear complex, [(AuCl)(4){p-C6H4{N{P(OC6H4C3H5-o)(2)}(2)}(2)}] (12). Complex 8 shows excellent catalytic activity in the Suzuki-Miyaura cross-coupling reaction under microwave conditions and complex 7 catalyzes hydroformylation of styrenes with good TONs.

Crystallographically characterised 3,6-bis(2'-pyridyl) pyridazine (L) forms complexes with {(acac)(2)Ru} or {(bpy)(2)Ru2+} via one pyridyl-N/pyridazyl-N chelate site in mononuclear Ru-II complexes (acac)(2)Ru(L), 1, and [(bpy)(2)Ru(L)] (ClO4)(2), [3] (ClO4)(2). Coordination of a second metal complex fragment is accompanied by deprotonation at the pyridazyl-C-5 carbon {L --> (L-H+)} to yield cyclometallated, asymmetrically bridged dinuclear complexes [(acac)(2)Ru-III (mu-L-H+) Ru-III (acac)(2)] (ClO4), [2] (ClO4), and [(bpy)(2)Ru-II (mu- L-H+) Ru-II (bpy)(2)] (ClO4)(3), [4] (ClO4)(3). The different electronic characteristics of the co-ligands, sigma donating acac(-) and pi accepting bpy, cause a wide variation in metal redox potentials which facilitates the isolation of the diruthenium(III) formin [2] (ClO4) with antiferromagnetically coupled Ru-III centres (J = 11.5 cm(-1)) and of a luminescent diruthenium(II) species in [4] (ClO4)(3). The electrogenerated mixed-valent (RuRuIII)-Ru-II states 2 and [4](4+) with comproportionation constants K-c > 10(8) are assumed to be localised with the Ru-III ion bonded via the negatively charged pyridyl-N/pyridazyl-C-5 chelate site of the bridging (L-H+)(-) ligand. In spectroelectrochemical experiments they show similar intervalence charge transfer bands of moderate intensity around 1300 nm and comparable g anisotropies (g(1)-g(3) approximate to 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the pi acceptor ligated system [4](4+), signifying stabilised metal d orbitals.

The tppz-bridged diruthenium complex [{(L)ClRuII}(2)(mu-tppz)](ClO4)(2), [1](ClO4), {tppz=2,3,5,6-tetrakis(2-pyridyl)-pyrazine, L=2,2'-dipyridylamine} and its mononuclear counterpart [(L)ClRuII(tppz)]ClO4, [2](ClO4) have been synthesized. The 380 mV separation between successive Ru-II/Ru-III couples in [1](2+) leads to a comproportionation constant (K-c) of 2.7x10(6). Consequently, the (RuRuIII)-Ru-II species [1](3+) exhibits a rather narrow intervalence charge transfer band at 1700 run, suggesting a class III mixed-valence state, the electronic coupling constant (V-ab) is calculated at 2940 cm(-1). Complex [1](3+) displays a rhombic EPR spectrum at 4 K (g(1)=3.390, g(2)=2.278, g(3)=1.697), characteristic of ruthenium(III) in a distorted octahedral environment. Both complexes show two successive tppz-based reduction processes [(tppz)(0/-1) and (tppz)(-1/-2)]. The one-electron reduced species [1](+) is a tppz radical anion species with an intense low-energy band at 1105 nm and an axial EPR signal at 4 K (g(1)=2.008, g(2)=g3=1.994). [1](2+) and [2](+) exhibit moderately strong emissions at 740 nm and 668 nm, respectively, in EtOH-MeOH glass at 77 K.

The first synthesis and electrochemistry of metalloporphyrins containing a bound PF3 axial ligand has been achieved. The investigated compounds are [Ru(por)(PF3)] where por is the dianion of 5,10,15,20-tetraphenyl-, -tetra(p-bromophenyl)-, -tetra(p-methoxyphenyl)-, 2,7,12,17-tetraethyl-3,8,13,18-tetramethyl- or 2,3,7,8,12,13,17,18-octaethyl-porphyrin. Each [Ru(por)(PF3)] species was investigated with respect to its spectroscopic and electrochemical properties and the resulting data compared with those for [Ru(por)(CO)] having the same porphyrin ring. A number of similarities exist between the carbonyl and PF3 derivatives in methylene chloride but major differences can be observed in other non-aqueous solutions. The first reduction of each complex is reversible in tetrahydrofuran (thf) and leads to a porphyrin π-anion radical rather than a ruthenium(I) species as identified by UV/VIS spectroelectrochemistry. Each investigated complex also undergoes two reversible oxidations in dichloromethane, the first of which leads to a porphyrin π-cation radical. The [Ru(por)(PF3)] derivatives appear to be more stable than the [Ru(por)(CO)] analogues in thf or CH2Cl2, but an electrochemically initiated conversion of [RuII(por)(PF3)(py)] into [RuIII(por)(py)2]+ can be readily accomplished in pyridine (py) or CH2Cl2–pyridine mixtures. This type of reaction has never been seen upon oxidation of a ruthenium(II) porphyrin and was monitored by cyclic voltammetry and UV/VIS spectroelectrochemistry.

Natural systems have marvelously utilized copper complexes featuring sulfur-coordinating ligands, known as blue copper proteins, as efficient electron-transfer mediators in biological processes. Copper complexes with sulfur-coordinating ligands have been attempted as redox mediators in dye-sensitized solar cells (DSCs), the performance of which is not yet satisfactory and still remains less well explored. Herein, we report the application of new copper complexes bearing a tetradentate polythioether ligand, [(S-4)Cu](2+/+) (1(2+/+), S-4 = 1,4,8,11-tetrathiocyclotetradecane), as a redox mediator in DSCs in comparison with its N-4-tetradentate counterpart [(N-4)Cu](2+/+) (2(2+/+), N-4 = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Impressively, the changes of coordination atoms from N to S positively shift the formal redox potential of the copper complexes by 600 mV, leading to a remarkably high photovoltage approaching 1.0 V. This is one of the highest photovoltage values reported thus far for DSCs based on copper redox mediators.

Two new dyes based on a dinuclear rhenium complex and (E)-3-(5-(4-(bis(2,4-dibutoxy-[1,1-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (namely D35) have been investigated as sensitizers for dye sensitized solar cells (DSSCs). Two different pyridazine ligands have been used, namely 4-pyridazine-carboxylic acid for dye 2 ([Re-2(-H)(-D35)(CO)(6)(-pyridazine-4-COOH)]) and 4-pyridazinyl-butanoic acid for dye 3 ([Re-2(-H)(-D35)(CO)(6)(-pyridazine-4-C3H6-COOH)]). The performances of these new dyes have been compared with those of the dye containing the bare 4-diphenylaminobenzoic acid, namely TPA, as the ancillary ligand (dye 1). Compared to dye 1, dyes 2 and 3 show an impressive tenfold increase in the absorption intensity in the range of 487-493 nm on TiO2 films, with great improvement of the light harvesting. Cyclic voltammetry experiments, performed on derivatives containing the methyl ester of the pyridazine ligands, show narrow electrochemical band gaps in the range of 1.36-1.84 eV. Solar cells with each dye have been prepared, using both iodide/triiodide and cobalt redox couples as the electrolytes, platinum or carbon as the counter electrodes, and TiO2 or SnO2 as the metal oxide photoelectrodes, respectively. The best DSSC results have been obtained using dye 3, with an overall solar-to-electric conversion efficiency of 3.5%, which greatly overcomes the previous result of 1.0% obtained for dye 1 in a not-optimized setup of the device. The performances of dye 3 are due to the presence of D35 ligand, which further suppresses the recombination of the injected electron with the electrolyte and with the oxidized state of the dye.

Aromatic amines are aquatic contaminants for which phototransformation in surface waters can be induced by excited triplet states of dissolved organic matter ((DOM)-D-3*). The first reaction step is assumed to consist of a one-electron oxidation process of the amine to produce its radical cation. In this paper, we present laser flash photolysis investigations aimed at characterizing the photoinduced, aqueous phase one-electron oxidation of 4-(dimethylamino) benzonitrile (DMABN) as a representative of this contaminant class. The production of the radical cation of DMABN (DMABN(center dot+)) after direct photoexcitation of DMABN at 266 nm was confirmed in accord with previous experimental results. Moreover, DMABN(center dot+) was shown to be produced from the reactions of several excited triplet photosensitizers (carbonyl compounds) with DMABN. Second-order rate constants for the quenching of the excited triplet states by DMABN were determined to fall in the range of 3 x 10(7)-5 x 10(9) M-1 s(-1), and their variation was interpreted in terms of electron transfer theory using a Rehm-Weller relationship. The decay kinetics of DMABN(-+) in the presence of oxygen was dominated by a second-order component attributed to its reaction with the superoxide radical anion (O-2(center dot-)). The first-order rate constant for the transformation of DMABN(center dot+) leading to photodegradation of DMABN was estimated not to exceed approximate to 5 x 10(3) s(-1).

A series of eight Ru(II) heteroleptic complexes incorporating an ancillary [2,2′]bipyridine functionalised at the [4,4′] positions with one (M-type) or two (B-type) thienylenevinylenes (nTVs, n = 2 or 4) is reported. Three types of substitutions have been used for nTVs: hexylthioether, hexyloxy and hexyl. The characterisation of the half-sandwich intermediates and final complexes is provided. In particular, the half-sandwich complexes in the M-type series are obtained as a racemate, whereas the heteroleptic complexes consist of two regioisomers. Finally, these complexes have been tested as dyes in dye-sensitized solar cells (DSSCs). Counterintuitively, better performances were obtained for M-type complexes with shorter 2TV moieties. The best performing dye was the Ru(II) complex mono-functionalized with a 2TV moiety having an hexylthioether substitution (M2S), which achieved a maximum power efficiency of 2.77% under full sun illumination (AM1.5G standard conditions). The structure–performance relationship in DSSCs is discussed based on photovoltaic and electrochemical data and DFT-calculations.