Photophysics and electron transfer in poly(3-octylthiophene) alternating with Ru(II)- and Os(II)-bipyridine complexes

Soluble reduced graphene oxide sheets grafted with polypyridylruthenium-derivatized polystyrene brushes as light harvesting antenna for photovoltaic applications

Soluble graphene nanosheets, prepared by grafting polystyrene-based polymer chains from the surface of reduced graphene oxide (RGO), have been functionalized with pendant Ru(II) polypyridine chromophores. N-Hydroxysuccinimide (NHS) derivatized p-vinylbenzoic acid polymer chains were grown from methyl bromoisobutyrate initiation sites on the surface of RGO by atom transfer radical polymerization (ATRP). Deprotection of the resulting NHS polystyrene chains followed by amide coupling with the amine-derivatized Ru(II) polypyridyl complex [Ru(4-CH2NH2-4'-CH3-bpy)(bpy)2](2+) (4-CH2NH2-4'-CH3-bpy = 4-aminomethyl-4'-methyl 2,2'-bipyridine and bpy = 2,2'-bipyridine) afforded the covalently linked RGO-metallopolymer. The hybrid graphene-polymer assembly has been fully characterized with clear evidence for covalent attachment of the metallopolymer brushes to the graphene substrate. On the basis of thermal gravimetric analysis, one polymer strand is grafted to the surface of RGO for every hundred graphene carbons. The covalently linked polymer brushes feature controlled chain lengths of ∼30 repeat units with a small polydispersity index (PDI, ∼ 1.2). Photovoltaic cells based on the derivatized polymers and graphene-polymer assemblies were evaluated. The graphene-polymer assembly in the configuration, ITO/PEDOT:PSS/RGO-PSRu/PC60BM/Al, exhibited enhanced photocurrent and power conversion efficiencies (∼5 fold) relative to devices with the configuration, ITO/PEDOT:PSS/PSRu/PC60BM/Al.

1-(4-Meth-oxy-phen-yl)-2-[4-(tri-fluoro-meth-yl)phen-yl]-1H-phenanthro[9,10-d]imidazole

In the title compound, C29H19F3N2O, a phenanthroline-fused imidazole tetra-cyclic system, the fused benzene rings deviate slightly from the central ring and make dihedral angles with this ring of 3.47 (8) and 3.05 (8)°. The tri-fluoro-methyl-phenyl ring is roughly coplanar with the phenanthroline-fused imidazole tetra-cyclic system [dihedral angle = 11.02 (6)°], while the meth-oxy-phenyl ring is almost perpendicular [dihedral angle = 87.65 (6)°]. There are intra-molecular C-H ⋯π inter-actions involving the meth-oxy-phenyl ring and the central phenanthroline ring, as well as an inter-molecular C-H⋯π inter-action involving the phenanthroline ring. In addition, there is an inter-molecular π-π inter-action involving the central phenanthroline ring and the tri-fluoro-methyl-phenyl ring [centroid-centroid distance = 3.685 (2) Å], as well as C-H⋯N inter-actions linking the mol-ecules into dimers.

Oxidative quenching within photosensitizer-acceptor dyads based on bis(bidentate) phosphine-connected osmium(II) bipyridyl light absorbers and reactive metal sites

For the first time oxidative quenching of OsP₂N₄ chromophores by reactive Pt^II or Pd^II sites containing cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) is directly observed despite the presence of a saturated cyclobutane backbone “bridge”. This dramatic effect is measured as a sudden temperature-dependent onset of a reduction in phosphorescence lifetime in [Os(bpy)₂(dppcb)MCl₂](SbF₆)₂ (M = Pt, 1; Pd, 2). The appearance of this additional energy release is not detectable in [Os(bpy)₂(dppcbO₂)](PF₆)₂ (3), where dppcbO₂ is cis, trans, cis-1,2-bis(diphenylphosphinoyl)-3,4-bis(diphenylphosphino)cyclobutane. Obviously, the square-planar metal centers in 1 and 2 are responsible for this effect. In line with these observations, the emission quantum yields at room temperature for 1 and 2 are drastically reduced compared with 3. Since this luminescence quenching implies strong intramolecular interaction between the Os^II excited states and the acceptor sites and depends on the metal⋯metal distances, also the single crystal X-ray structures of 1–3 are given.

1-(3,5-Dimethyl-phen-yl)-2-(4-fluoro-phen-yl)-1H-phenanthro[9,10-d]imidazole

In the title compound, C₂₉H₂₁FN₂, the phenanthro tricyclic ring system is essentially planar with a maximum deviation of 0.030 (2) Å and makes dihedral angles between of 77.96 (6) and 37.18 (7)° with the dimethyl­phenyl and fluoro­phenyl rings, respectively. The crystal packing features weak C—H⋯π inter­actions involving the dimethyl­phenyl and other phenyl rings.

Light-harvesting cross-linked polymers for efficient heterogeneous photocatalysis

Nonporous, phosphorescent cross-linked polymers (Ru-CP and Ir-CP) were synthesized via Pd-catalyzed Sonogashira cross-coupling reactions between tetra(p-ethynylphenyl)methane and dibrominated Ru(bpy)(3)(2+) or Ir(ppy)(2)(bpy)(+), respectively. The resultant particulate cross-linked polymer (CP) materials have very high catalyst loadings (76.3 wt % for Ru-CP and 71.6 wt % for Ir-CP), and are nonporous with negligibly small surface areas (2.9 m(2)/g for Ru-CP and 2.7 m(2)/g for Ir-CP). Despite their nonporous nature, the insoluble CP materials serve as highly active and recyclable heterogeneous photocatalysts for a range of organic transformations such as aza-Henry reaction, aerobic amine coupling, and dehalogenation of benzyl bromoacetate. An efficient light-harvesting mechanism, which involves collection of photons by exciting the (3)MLCT states of the phosphors and migration of the excited states to the particle surface, is proposed to account for the very high catalytic activities of these nonporous CPs. Steady-state and time-resolved emission data, as well as the reduced catalytic activity of Os(bpy)(3)(2+)-doped Ru-CPs supports efficient excited state migration for the CP frameworks. This work uncovers a new strategy in designing highly efficient photocatalysts based on light-harvesting cross-linked polymers.

Conjugation length dependent ground and excited state electronic behavior in oligothienyl ru complexes

Photoexcitation of a bis(bipyridyl) Ru(II) complex bearing a phosphinopentathiophene ligand results in formation of a transient species with a lifetime of 2.2 micros. The transient is attributed to the product of an intramolecular charge transfer from the pentathiophene ligand. EPR and UV/vis spectroelectrochemistry show that the HOMO is pentathienyl-based, while corresponding complexes with shorter conjugation length ligands have a metal-based HOMO and do not exhibit long-lived transients.

Spectroscopic and Redox Properties of Novel d6-Complexes Engineered from All Z-Ethenylthiophene-bipyridine Ligands

A series of quasilinear dinuclear complexes incorporating ruthenium(II)- and osmium(II)-tris(2,2'-bipyridine) units has been prepared in which the individual metal-containing moieties are separated by 3,4-dibutyl-2,5-diethenylthiophene spacers and end-capped by 3,4-dibutyl-2-ethenylthiophene subunits; related ruthenium(II) and osmium(II) mononuclear complexes have also been prepared where one bpy unit is likewise end-capped by 3,4-dibutyl-2-ethenylthiophene subunits [bpy = 2,2'-bipyridine]. Overall, mononuclear species, labeled here Ru and Os, and dinuclear species, RuRu, OsOs, and RuOs, have been prepared and investigated. Their electrochemical behavior has been studied in CH3CN solvent and reveals ethenylthiophene-centered oxidations (irreversible steps at > +1.37 V vs SCE), metal-centered oxidations (reversible steps at +1.30 V vs SCE for Ru(II/III) and +0.82 V vs SCE for Os(II/III)), and successive reduction steps localized at the substituted bpy subunits. The spectroscopic studies performed for the complexes in CH3CN solvent provided optical absorption spectra associated with transitions of ligand-centered nature (LC, from the bpy and ethenylthiophene subunits) and metal-to-ligand charge-transfer nature (MLCT), with the former dominating in the visible region (400-600 nm). While the constituent ethenylthiophene-bpy ligands are strong fluorophores (fluorescence efficiency in CH2Cl2 solvent, phi em = 0.49 and 0.39, for the monomer and the dimer, respectively), only weak luminescence is observed for each complex in acetonitrile at room temperature. In particular, (i) the complexes Ru and RuRu do not emit appreciably, and (ii) the complexes Os, OsOs, and RuOs exhibit triplet emission of 3Os --> L CT character, with phi em in the range from 10-3 to 10-4. These features are rationalized on the basis of the role of nonemissive triplet energy levels, 3Th, centered on the ethenylthiophene spacer. These levels appear to lie lower in energy than the 3Ru --> L CT triplet levels, and in turn higher in energy than the 3Os --> L CT triplet levels, along the sequence 3Ru --> L CT > 3Th > 3Os --> L CT.

Photophysical Properties of Ruthenium(II) Tris(2,2‘-bipyridine) Complexes Bearing Conjugated Thiophene Appendages

A small series of ruthenium(II) tris(2,2'-bipyridine) complexes has been synthesized in which ethynylated thiophene residues are attached to one of the 2,2'-bipyridine ligands. The photophysical properties depend on the conjugation length of the thiophene-based ligand, and in each case, dual emission is observed. The two emitting states reside in thermal equilibrium at ambient temperature and can be resolved by emission spectral curve-fitting routines. This allows the properties of the two states to be evaluated in both fluid butyronitrile solution and a transparent KBr disk. It is concluded that both emitting states are of metal-to-ligand charge-transfer (MLCT) character, and despite the presence of conjugated thiophene residues, there is no indication for a low-lying pi,pi*-triplet state that promotes nonradiative decay of the excited-state manifold. A key feature of these systems is that the conjugation length imposed by the thiophene-based ligand helps to control the rate constants for both radiative and nonradiative decay from the two MLCT triplet states.

Photoelectrochemistry of Conducting Polymers Modified with Electron-Acceptor Moieties

The photoelectrochemical behavior of two polymers of the polythiophene series containing electron-acceptor groups in the main chain was studied and compared to that of the nonmodified polymer, poly(2,2'-bithiophene), PBT. The acceptor groups were 2,2'-bipyridine and biphenyl, which are electron-deficient as compared to the bithiophene unit. All three polymers demonstrated a pronounced photovoltaic effect, which for PBT was consistent with data reported earlier. The introduction of the electron-acceptor moieties was found to significantly enhance the magnitude of the steady-state photocurrent as well as to drastically alter the dependencies of the photocurrent on the polymer film thickness and the external bias. These observations indicated that the mechanism of photocurrent generation in the modified polymers differs from that in nonmodified polymer and involves the electron transfer to the electron-acceptor moieties in the polymer main chain. The values of the external quantum efficiency were estimated in a liquid-cell arrangement to be 0.27 and 0.19% for modified and nonmodified polymers, respectively.

Binuclear wirelike dimers based on ruthenium(II)-bipyridine units linked by ethynylene-oligothiophene-ethynylene bridges

The syntheses, structural characteristics, electrochemical behavior, ground-state spectra, photophysical properties, and transient absorption (TA) spectra in CH(3)CN solvent are reported for binuclear [(bpy)(2)Ru(bpy-E(T)(n)()E-bpy)Ru(bpy)(2)](4+) complexes, Ru(bpyT(n)bpy)Ru, where the Ru-based units are connected by alternating 3,4-dibutylthiophene (DBT')/thiophene (T') fragments linked via ethynyl groups (E) to bpy ligands at the 5-position (bpy is 2,2'-bipyridine). The ligand bpyT(3)bpy represents a module containing DBT'/T'/DBT' subunits, and bpyT(5)bpy accounts for a DBT'/T'/DBT'/T'/DBT' pattern. The syntheses and electrochemical and spectroscopic (emission and TA) properties in CH(2)Cl(2) solvent of the bpyT(n)()bpy ligands are likewise reported. The behavior of the Ru(bpyT(n)bpy)Ru dimers has been compared to that of the bpyT(n)bpy ligands and to that of a related mononuclear complex, [(bpy)(2)Ru(bpy-E-DBT')](2+), Ru(bpyDBT'). For the dimeric complexes, the electrochemical results show that the first reduction step takes place at the bpy ligand(s) bearing an ethynylene group, the first oxidation step is thiophene-centered, and further oxidation involves the metal centers, which are only weakly interacting. The photophysical and TA results for the Ru(bpyT(n)bpy)Ru dimers account for the presence of low-lying oligothiophene-centered (3)pi,pi levels, while higher-lying metal-ligand charge transfer ((3)MLCT) levels are thermally accessible only for the case of Ru(bpyT(3)bpy)Ru; the possible role of charge separation (CS) levels (from oxidation at the thiophene bridge and reduction at one of the coordinated bpy's) is also discussed.

Energy Transfer in Hybrids Based on a Thiophene-Substituted Ethynylbipyridine Dimer Decorated with Re(I), Ru(II), and Os(II) Units

The preparation, structural features, electrochemical behavior, and optical properties (at room temperature and at 77 K) are reported for a series of thiophene-containing hybrids based on the bent conjugated backbone of a rigid ditopic ligand, the dimeric moiety 3,4-dibutyl-2,5-bis{5'-[(3,4-dibutylthien-2-ylethynyl)-2,2'-bipyridin-5-yl]ethynyl}thiophene (TBTBT). Within the dimer, the diethynyl-2,2'-bipyridine units (bpy, the coordination sites) alternate with three 3,4-dibuthylthiophene units and coordination of the [Re(CO)3Cl], [Ru(bpy)2]2+, and [Os(bpy)2]2+ centers results in the mononuclear species RuTBTBT and OsTBTBT and the binuclear species RuTBTBTRu, OsTBTBTOs, RuTBTBTOs, and ReTBTBTOs. At room temperature, the emitting states obtained by photoexcitation are of 3MLCT nature, and vibronic analysis of the emission spectra indicates that they are largely delocalized over the TBTBT ligand. In the binuclear species, the intermetal separation is ca. 17 A, and for RuTBTBTOs, an efficient Ru --> Os excitation transfer takes place, resulting solely in an Os-based emission. The process is ascribed to double-electron transfer (Dexter), as mediated by the TBTBT ligand; a similar conclusion holds for the case of ReTBTBTOs. For RuTBTBTOs, the process is discussed in some detail also with regard to the possibility of disentangling the constituent hole and electron-transfer events.

Oligothiophene Bipyridine Alternate Copolymers and Their Ruthenium Metalated Analogues: In Situ ESR and UV−Vis Investigations of Metal−Chain Interactions

In situ electron spin resonance (ESR) and UV-vis spectro-electrochemical studies have been performed on two copolymers consisting of alternating subunits of regioregular head to tail (HT) coupled 3-octylthiophene tetramer and 2,2'-bipyridine subunits (P4) or 3-octylthiophene hexamer subunits of the same regioregularity and 2,2'-bipyridine subunits (P6). Both P4 and P6 have been investigated in their metal-free form as well as in the ruthenium(II) metalated form (P4-Ru and P6-Ru). P4 and P6 in the p-doped state exhibit a clear ESR signal characteristic of the presence of polarons in the oligothienylene subunits. In the case of P4, no recombination of polarons into bipolarons is observed, whereas the recombination process takes place in P6. The formation of bipolarons is well-rationalized in terms of the conjugation length, and it seems clear that the higher length of the oligothiophene subunit in P6( )()stabilizes bipolarons(.)() The same effect, is induced by the coordination of -Ru(bpy)(2)(2+) to the bipyridine unit in the metalated form of both polymers, which results in an increase of the conjugation length. Important information is gained from the analysis of the ESR spectra of both nonmetalated and metalated in the oxidized (p-doped) and reduced (n-doped) forms. In the p-doped state both nonmetalated and metalated polymers reveal the presence of a narrow ESR line characteristic of the mobile spin carriers in the polymer matrix. The oxidation of the metal center occurs at higher potentials and leads to an irreversible destruction of the system. To the contrary, in the reduced (n-doped) state the ESR lines of the nonmetalated and metalated polymers markedly differ. A significant line broadening with simultaneous change of the g-value is caused by spin-orbit coupling phenomenon induced by the presence of the coordinating metal. Finally, the observation of a clear polaronic band in the UV-vis spectrum of p-doped P4 and its strong dependence on the applied potential can be clearly correlated with the potential induced changes in the ESR spin density. The same applies to P4-Ru, where the changes in the polaronic and bipolaronic bands can also be correlated with the ESR spin density changes.

Oligomeric ligands incorporating multiple 5,5'-diethynyl-2,2'-bipyridine moieties bridged and end-capped by 3,4-dibutylthiophene units

In this work, we detail the synthesis and photophysical properties of a series of soluble polybipyridine ligands comprising one to five bipyridine units sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units. The dual Sonogashira coupling reaction of 5,5'-dibromo-2,2'-bipyridine with TMS- and (CH3)2C(OH)-protected acetylene allows the synthesis of a dissymmetrically functionalized building block which was selectively deprotected at either the TMS or 2-hydroxyprop-2-yl site. Various combinations allow the interconnection of the terminal alkyne to 3,4-dibutyl-2,5-diiodothiophene or 3,4-dibutyl-2-iodothiophene leading to bipyridine frameworks bearing two acetylene-protected groups or one acetylenethiophene/one acetylene-protected function. It is possible therefore to construct dimeric to pentameric bipyridine ligands where the chelating subunit is bridged by a 3,4-dibutyl-2,5-diethynylthiophene spacer and end-capped by a 3,4-dibutyl-2-ethynylthiophene stopper. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions. Spectroscopic data for the new oligomers are discussed in terms of the extent of pi-electron conjugation. Upon increasing the number of pi-electrons from 24 to 104, there is a progressive lowering in the energy of absorption and fluorescence transitions, while the emission quantum yields remain essentially constant. The LUMO levels of these large molecules, estimated by cyclic voltammetry, lie in the range -3.06 to -3.18 eV.

Reversible Molecular Switching of Ruthenium Bis(bipyridyl) Groups Bonded to Oligothiophenes: Effect on Electrochemical and Spectroscopic Properties

We report the preparation of complexes in which ruthenium(II) bis(bipyridyl) groups are coordinated to oligothiophenes via a diphenylphosphine linker and a thienyl sulfur (P,S bonding) to give [Ru(bpy)(2)PT(3)-P,S](PF(6))(2) (bpy = 2,2'-bipyridyl, PT(3) = 3'-(diphenylphosphino)-2,2':5',2' '-terthiophene), [Ru(bpy)(2)PMeT(3)-P,S](PF(6))(2) (PMeT(3) = 3'-(diphenylphosphino)-5-methyl-2,2':5',2' '-terthiophene), [Ru(bpy)(2)PMe(2)T(3)-P,S](PF(6))(2) (PMe(2)T(3) = 5,5' '-dimethyl-3'-(diphenylphosphino)-2,2':5',2' '-terthiophene), and [Ru(bpy)(2)PDo(2)T(5)-P,S](PF(6))(2) (PDo(2)T(5) = 3,3' '' '-didodecyl-3' '-diphenylphosphino-2,2':5',2' ':5' ',2' '':5' '',2' '' '-pentathiophene). These complexes react with base, resulting in the complexes [Ru(bpy)(2)PT(3)-P,C]PF(6), [Ru(bpy)(2)PMeT(3)-P,C]PF(6), [Ru(bpy)(2)PMe(2)T(3)-P,C]PF(6), and [Ru(bpy)(2)PDo(2)T(5)-P,C]PF(6), where the thienyl carbon is bonded to ruthenium (P,C bonding). The P,C complexes revert back to the P,S bonding mode by reaction with acid; therefore, metal-thienyl bonding is reversibly switchable. The effect of interaction of the metal groups in the different bonding modes with the thienyl backbone is reflected by changes in alignment of the thienyl rings in the solid-state structures of the complexes, the redox potentials, and the pi --> pi transitions in solution. Methyl substituents attached to the terthiophene groups allow observation of the effect of these substituents on the conformational and electronic properties and aid in assignments of the electrochemical data. The PT(n)() ligands bound in P,S and P,C bonding modes also alter the electrochemical and spectroscopic properties of the ruthenium bis(bipyridyl) group. Both bonding modes result in quenching of the oligothiophene luminescence. Weak, short-lived Ru --> bipyridyl MLCT-based luminescence is observed for [Ru(bpy)(2)PDo(2)T(5)-P,S](PF(6))(2), [Ru(bpy)(2)PT(3)-P,C]PF(6), [Ru(bpy)(2)PMeT(3)-P,C]PF(6), and [Ru(bpy)(2)PMe(2)T(3)-P,C]PF(6), and no emission is observed for the alternate bonding mode of each complex.

Exciton-like energy collection in an oligothiophene wire end-capped by Ru- and Os-polypyridine chromophores

Ru(II)- and Os(II)-polypyridine termini are linked by a quinquethiophene bridge (the inter-metal separation is ca. 1.9 nm) wherein excitation energy flows into the luminescent Os-based unit by way of a conductive level.

Ruthenium bis-terpyridine complexes connected to an oligothiophene unit for dry dye-sensitised solar cells

The preparation of a series of new heteroleptic ruthenium complexes containing a 4'-phosphonic acid terpyridine and a terpyridine substituted in 4' position by a bithiophene or tert-thiophene are described. The UV-Vis absorption and emission spectra along the redox potentials of these complexes are reported. These new complexes were also tested as sensitizers in dry dye-sensitised solar cell using regioregular polyoctylthiophene as a solid hole conductor. It has been shown that the complexes substituted with thiophene chain exhibit poor photovoltaic efficiency most probably due to low electron injection efficiency. This latter property can be rationalised by the fact that the LUMO orbitals in these complexes are localised in the terpyridine substituted by the thiophene chain and not in the terpyridine phosphonic which is bonded to the TiO2 photoanode.

Synthesis and electronic properties of series of oligothiophene-[1,10]phenanthrolines

Organic semiconductors containing metal binding sites within their molecular backbones are of a general interest in organic materials chemistry. In this paper, we describe a straightforward synthetic procedure, which gives access to a series of 2-(oligothienyl)-[1,10]phenanthrolines (nT-phen), 2,9-bis(oligothienyl)-[1,10]phenanthrolines (nT-phen-nT) and 2,2'-(oligothienyl)bis-[1,10]phenanthrolines (phen-nT-phen). By a Negishi-type cross coupling of 2-iodo-[1,10]phenanthroline or 2,9-diiodo-[1,10]phenanthroline with in situ generated alpha-zinc derivatives of different mono-, ter-, and quinquethiophenes we were able to synthesize the corresponding oligothienyl-phenanthrolines in medium to excellent yields. Furthermore, characterization of the optical properties of the new materials indicated that the two subunits, oligothiophene and phenanthroline, are in pi-conjugation. Characterization of the redox properties revealed additional evidence for the role of [1,10]phenanthroline as a pi-bridging unit in the nT-phen-nT series.

A New Class of Near-Infrared Electrochromic Oxamide-Based Dinuclear Ruthenium Complexes

We report the synthesis of a new class of symmetric and unsymmetric oxamide-based dinuclear ruthenium complexes. These complexes were characterized by NMR, ESI-MS, and electrochemical methods. Spectroelectrochemical analysis of the complexes showed broad absorptions in the NIR region for the mixed-valence state of the complexes. The introduction of a chiral group into the bridging ligand produced an optically active complex that was studied using circular dichroism. [structure: see text]

Mononuclear and Binuclear Wirelike Ruthenium(II) Complexes with Oligo-diethynyl-thiophene Bridged Back-to-Back Terpyridine Ligands: Synthesis and Electrochemical and Photophysical Properties

The syntheses, structural features, electrochemical behavior, absorption spectra, and photophysical properties of five mononuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)](2+), RuT(n), and five binuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)Ru(terpy)](4+), RuT(n)Ru, are reported, where n varies from 1 to 5 so that the metal-metal distance is estimated to be 42 A for the largest binuclear complex, RuT(5)Ru (terpy is 2,2':6',2"-terpyridine and DEDBT is 2,5-diethynyl-3,4-dibutylthiophene). The metal-centered oxidation potentials for the mononuclear and binuclear species are slightly more positive than for the reference [Ru(terpy)(2)](2+) complex, owing to the withdrawing nature of the back-to-back terpyridine ligands incorporating the repeat diethynyl-thiophene units. Comparison of the reduction potentials for the mononuclear and binuclear complexes reveals that the reduction steps are localized either at the terpy fragments of the T(n) ligands or at the terpy peripheral ligands. The spectroscopic results (absorption spectra at room temperature, luminescence spectra and lifetimes at room temperature and at 77 K) in acetonitrile solvent are consistent with the establishment of electronic delocalization within the oligomeric diethynyl-thiophene fragments (DEDBT(n)) of the T(n) ligands; however, the results also indicate that the terpy units of these ligands and the DEDBT(n)fragments are not strongly coupled. Both at room temperature and at 77 K, the (3)metal-to-ligand charge-transfer luminescence of RuT(n) and RuT(n)Ru complexes is strongly depressed in the larger species with respect to what happens for n < or = 2 (where the luminescence quantum yield is phi approximately 10(-4)); this is discussed in terms of the possible intervention of triplet levels localized at the oligothiophene DEDBT(n)(fragments.

Photophysical properties of closely-coupled, binuclear ruthenium(ii) bis(2,2′:6′,2″-terpyridine) complexes

The photophysical properties of closely-coupled, binuclear complexes formed by connecting two ruthenium(II) bis(2,2':6',2''-terpyridine) complexes via an alkynylene group are compared to those of the parent complex. The dimers exhibit red-shifted emission maxima and prolonged triplet lifetimes in deoxygenated solution. Triplet quantum yields are much less than unity and the dimers generate singlet molecular oxygen with low quantum efficiency. Temperature dependence emission studies indicate coupling to higher-energy triplet states while cyclic voltammetry shows that the metal centres are only very weakly coupled but that extensive electron delocalization occurs upon one-electron reduction. The radiative rate constants derived for these dimers are relatively low, because the lowest-energy metal-to-ligand, charge-transfer states possess increased triplet character. In contrast, the rate constants for nonradiative decay of the lowest-energy triplet states are kept low by extended electron delocalization over the polytopic ligand. The poor triplet yields are a consequence of partitioning at the second triplet level.

Synthesis and solution characterization of [Ru(bpy)2]2+ modified polyazines

A series of [Ru(bpy)(2)](2+) complexes linked by a controlled number of azine units (one to seven) were synthesized and studied in the solution phase. Polymers and dimer model compounds were examined by cyclic voltammetry and IR, NMR, and visible-NIR spectroscopies. The NMR spectra and the cyclic voltammograms indicated that the Ru(2+) sites influenced the main chain properties at least 15 A from the metal site. The first oxidation in each material was assigned to a ligand-centered process, but DFT calculations suggested that the Ru(2+) has an important influence. The first oxidized state of the polymers has a spectroscopic band that is consistent with an intervalence transfer (IT) transition, but this absorption is not seen in the dimer model compounds. Thus, the IT feature is assigned to a ligand-ligand transition that spans several repeat units in the polymer.

A concise modular synthesis of 2,5-diethynyl-3,4-dibutyl-thiophene-bridged back-to-back terpyridine ligands

The efficient synthesis of soluble and rigid terpyridine-based ditopic ligands bearing an increasing number of 2,5-diethynyl-3,4-dibutylthiophene (DEDBT) modules has demonstrated the advantages of a single convergent strategy based on a double coupling in a final step of monoterpyridine building blocks carrying the adequate number of thiophene modules with a diiodo-substituted thiophene subunit. This protocol enjoys the advantages of both efficiency and versatility and requires pivotal intermediates, which were produced by a step-by-step implementation of monoterpyridine fragments with a key thiophene intermediate carrying an iodo function, a propargylic-protecting group, and two butyl-solubilizing fragments. One set of experimental conditions is required to produce all the intermediates and the final ligands. Oxidative dimerization of monosubstituted terpyridine skeletons bearing one or two thiophene substituents and a terminal alkyne function, in the presence of cupric salts and oxygen, afforded the homotopic ligands with a central dithienylbutadiyne spacer. Optical properties for the new oligomers have been investigated and are discussed in terms of effective conjugation length and pi-electron conjugation. Upon increasing the number of interspersed DEDBT units, a significant lowering in energy of absorption and fluorescence transitions as well as of the quantum yields is observed.