Bipyridyl Ligands Research Articles

Supramolecular assembly promotes the electrocatalytic reduction of carbon dioxide by Re(I) bipyridine catalysts at a lower overpotential.

The addition of methyl acetamidomethyl groups at the 4,4'-positions of a 2,2'-bipyridyl ligand is found to enhance the rate of a bimolecular reduction mechanism of CO2 by Re(I) fac-tricarbonyl chloride complexes. Electrochemical studies, spectroelectrochemical measurements, and molecular dynamics simulations indicate that these methyl acetamidomethyl groups promote the formation of a hydrogen-bonded dimer. This supramolecular complex catalyzes the reductive disproportionation of CO2 to CO and CO3(2-) at a lower overpotential (ca. 250 mV) than the corresponding single-site 2 e(-) reduction of CO2 to CO and H2O catalyzed by the corresponding model complex with a 4,4'-dimethyl-2,2'-bipyridyl ligand. These findings demonstrate that noncovalent self-assembly can modulate the catalytic properties of metal complexes by favoring alternate catalytic pathways.

A new polyoxometalate-based Mo/V coordinated crystalline hybrid and its catalytic activity in aerobic hydroxylation of benzene

A novel self-assembled polyoxometalate-based Mo/V coordinated crystalline organic–inorganic hybrid compound [Mo2V2O8(2,2′-bpy)6][HPMo10V2O40]·2H2O (bpy = bipyridyl) was hydrothermally synthesized by introducing polyoxometalate into a metal–organic unit containing metal nodes and 2,2′-bipyridyl ligands. The unit of the crystal consists of one Keggin-structure heteropolyoxoanion [HPMo10V2O40]4−, one tetranuclear organic–metal coordination cation [Mo2V2O8(2,2′-bpy)6]4+ and two water molecules. The crystalline hybrid presents heterogeneous catalytic performance and superior activity towards benzene hydroxylation with molecular oxygen as the oxidant and ascorbic acid as the sacrificial reducing agent, giving a phenol yield of 12.5% and a high TON (turnover number) of 41. The result indicates that the polyoxometalate-based crystalline organic–inorganic hybrid compound provides an efficient heterogeneous catalyst for the liquid-phase aerobic hydroxylation of benzene to phenol.

Pt(II) bipyridyl complexes bearing substituted fluorenyl motif on the bipyridyl and acetylide ligands: synthesis, photophysics, and reverse saturable absorption.

A series of Pt(II) diimine complexes bearing benzothiazolylfluorenyl (BTZ-F8), diphenylaminofluorenyl (NPh2-F8), or naphthalimidylfluorenyl (NI-F8) motifs on the bipyridyl or acetylide ligands (Pt-4-Pt-8), (i.e., {4,4'-bis[7-R1-F8-(≡)n-]bpy}Pt(7-R2-F8- ≡ -)2, where F8 = 9,9'-di(2-ethylhexyl)fluorene, bpy = 2,2'-bipyridine, Pt-4: R1 = R2 = BTZ, n = 0; Pt-5: R1 = BTZ, R2 = NI, n = 0; Pt-6: R1 = R2 = BTZ, n = 1; Pt-7: R1 = BTZ, R2 = NPh2, n = 1; Pt-8: R1 = NPh2, R2 = BTZ, n = 1) were synthesized. Their ground-state and excited-state properties and reverse saturable absorption performances were systematically investigated. The influence of these motifs on the photophysics of the complexes was investigated by spectroscopic methods and simulated by time-dependent density functional theory (TDDFT). The intense absorption bands below 410 nm for these complexes is assigned to predominantly (1)π,π* transitions localized on either the bipyridine or the acetylide ligands; while the broad low-energy absorption bands between 420 and 575 nm are attributed to essentially (1)MLCT (metal-to-ligand charge transfer)/(1)LLCT (ligand-to-ligand charge transfer) transitions, likely mixed with some (1)ILCT (intraligand charge transfer) transition for Pt-4-Pt-7, and predominantly (1)ILCT transition admixing with minor (1)MLCT/(1)LLCT characters for Pt-8. The different substituents on the acetylide and bipyridyl ligands, and the degrees of π-conjugation in the bipyridyl ligand influence both the (1)π,π* and charge transfer transitions pronouncedly. All complexes are emissive at room temperature. Upon excitation at their respective absorption band maxima, Pt-4, Pt-6, and Pt-8 exhibit acetylide ligand localized (1)π,π* fluorescence and (3)MLCT/(3)LLCT phosphorescence in CH2Cl2, while Pt-5 manifests (1)ILCT fluorescence and (3)ILCT phosphorescence. However, only (1)LLCT fluorescence was observed for Pt-7 at room temperature. The nanosecond transient absorption study was carried out for Pt-4-Pt-8 in CH3CN. Except for Pt-7 that contains NPh2 at the acetylide ligands, Pt-4-Pt-6 and Pt-8 all exhibit weak to moderate excited-state absorption in the visible spectral region. Reverse saturable absorption (RSA) of these complexes was demonstrated at 532 nm using 4.1 ns laser pulses in a 2 mm cuvette. The strength of RSA follows this trend: Pt-4 > Pt-5 > Pt-7 > Pt-6 > Pt-8. Incorporation of electron-donating substituent NPh2 on the bipyridyl ligand significantly decreases the RSA, while shorter π-conjugation in the bipyridyl ligand increases the RSA. Therefore, the substituent at either the acetylide ligands or the bipyridyl ligand could affect the singlet and triplet excited-state characteristics significantly, which strongly influences the RSA efficiency.

ChemInform Abstract: Anionic Bipyridyl Ligands for Applications in Metallasupramolecular Chemistry.

The facile synthesis of anionic bipyridyl ligands with dinuclear clathrochelate cores is described. These metalloligands can be obtained in high yields by the reactions of M(ClO4)(2)(H2O)(6) (M: Zn, Mn, or Co) with 4-pyridylboronic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-diformyl-4-tert-butylphenol oxime, followed by deprotonation. The ligands are interesting building blocks for metallasupramolecular chemistry, as evidenced by the formation of a Pt-based molecular square and four coordination polymers with 2D or 3D network structures. Competition experiments reveal that the utilization of anionic bipyridyl ligands can result in significantly more stable assemblies.

A homologous series of [Fe(H₂Bpz₂)₂(L)] spin-crossover complexes with annelated bipyridyl co-ligands.

Four new iron(II) complexes [Fe(H2Bpz2)2(L)] were prepared (pz = pyrazolyl), where L is dipyrido[3,2-f:2',3'-h]quinoxaline (dpq), dipyrido[3,2-a:2'3'-c]phenazine (dppz), dipyrido[3,2-a:2'3'-c]benzo[i]-phenazine (dppn), and dipyrido[3,2-a:2',3'-c](6,7,8,9-tetrahydro)phenazine (dppc). Crystal structures of [Fe(H2Bpz2)2(dpq)], [Fe(H2Bpz2)2(dppz)], and [Fe(H2Bpz2)2(dppn)] all reveal stacks of complex molecules formed through π-π stacking between interdigitated bipyridyl chelate ligands, often with additional intercalated toluene or uncoordinated bipyridyl ligand (dpq). Molecules of [Fe(H2Bpz2)2(dppc)] form a different stacking motif in the crystal, with weaker contacts between individual molecules. Many of the structures also contain channels of disordered solvent, running between the molecular stacks. Despite their different stacking motifs, all these compounds exhibit very gradual thermal spin-crossover (SCO) on cooling, which occur over different temperature ranges but are otherwise quite similar in form. Weak thermal hysteresis in one of these spin equilibria can be attributed to the effects of a change in bipyridyl ligand conformation in the molecular stacks around 150 K, which was observed crystallographically. These results demonstrate that strong mechanical coupling between molecules in a crystal is not sufficient to engineer cooperative SCO switching, if other regions of the lattice are less densely packed.

Thermally activated delayed fluorescence (TADF) and enhancing photoluminescence quantum yields of [Cu(I)(diimine)(diphosphine)](+) complexes-photophysical, structural, and computational studies.

The complexes [Cu(I)(POP)(dmbpy)][BF4] (1) and [Cu(I)(POP)(tmbpy)][BF4] (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl; tmbpy = 4,4',6,6'-tetramethyl-2,2'-bipyridyl; POP = bis[2-(diphenylphosphino)-phenyl]ether) have been studied in a wide temperature range by steady-state and time-resolved emission spectroscopy in fluid solution, frozen solution, and as solid powders. Emission quantum yields of up to 74% were observed for 2 in a rigid matrix (powder), substantially higher than for 1 of around 9% under the same conditions. Importantly, it was found that the emission of 2 at ambient temperature represents a thermally activated delayed fluorescence (TADF) which renders the compound to be a good candidate for singlet harvesting in OLEDs. The role of steric constraints within the complexes, in particular their influences on the emission quantum yields, were investigated by hybrid-DFT calculations for the excited triplet state of 1 and 2 while manipulating the torsion angle between the bipyridyl and POP ligands. Both complexes showed similar flexibility within a ±10° range of the torsion angle; however, 2 appeared limited to this range, whereas 1 could be further twisted with little energy demand. It is concluded that a restricted flexibility leads to a reduction of nonradiative deactivation and thus an increase of emission quantum yield.

Assembly, characterization, and electrochemical properties of immobilized metal bipyridyl complexes on silicon(111) surfaces.

Silicon(111) surfaces have been functionalized with mixed monolayers consisting of submonolayer coverages of immobilized 4-vinyl-2,2'-bipyridyl (1, vbpy) moieties, with the remaining atop sites of the silicon surface passivated by methyl groups. As the immobilized bipyridyl ligands bind transition metal ions, metal complexes can be assembled on the silicon surface. X-ray photoelectron spectroscopy (XPS) demonstrates that bipyridyl complexes of [Cp*Rh], [Cp*Ir], and [Ru(acac)2] were formed on the surface (Cp* is pentamethylcyclopentadienyl, acac is acetylacetonate). For the surface prepared with Ir, X-ray absorption spectroscopy at the Ir LIII edge showed an edge energy as well as post-edge features that were essentially identical with those observed on a powder sample of [Cp*Ir(bpy)Cl]Cl (bpy is 2,2'-bipyridyl). Charge-carrier lifetime measurements confirmed that the silicon surfaces retain their highly favorable photoelectronic properties upon assembly of the metal complexes. Electrochemical data for surfaces prepared on highly doped, n-type Si(111) electrodes showed that the assembled molecular complexes were redox active. However the stability of the molecular complexes on the surfaces was limited to several cycles of voltammetry.

Photoprocess of molecules encapsulated in porous solids X: Photosensitization of zeolite-Y encapsulated tris(2,2′-bipyridine– nickel-(II)ion by phenosafranine adsorbed onto the external surface of the nanoporous host

Tris-(2,2′-bipyridine)-nickel-(II) complex ion encapsulated by zeolite-Y host has been synthesized by ship-in-a-bottle method. Photosensitization of nickel(II) complex (Ni(bpy)\(_{\mathrm {3}}^{\mathrm {2+}})\) in the zeolite host by surface adsorbed phenosafranine dye was investigated by time-resolved fluorescence and absorption spectral measurements. Formation of nickel (II)-complex in the super cage of the host was ascertained by XRD, FTIR, solid-state NMR, diffuse reflectance UV-visible absorption spectroscopic techniques and ICP-OES measurements. Phenosafranine dye adsorbed on the external surface of zeolite-Y shows a decrease in fluorescence intensity with increased loading of the nickel(II) complex in zeolite-Y. Time-resolved emission studies show two excited state lifetimes for the photoexcited phenosafranine dye. Average fluorescence lifetimes of the dye in this case do not change with increase in the loading of the nickel(II) complex. However, relative contribution of short lifetime component increases when the amount of encapsulated nickel(II) complex is increased. The zeolite-Y host containing only bipyridyl ligand shows a marked decrease in fluorescence intensity. Fluorescence lifetimes of the dye however do not change with increased loading of bipyridyl while relative contribution of short lifetime component increases with an increase in the loading of bipyridyl in the host. This observation is interpreted to be due to electron transfer from the excited state of phenosafranine dye to the bipyridine. Picosecond pump-probe investigations confirm that the photoinduced electron transfer occurs from the surface-adsorbed phenosafranine in the excited state to the nickel(II) complex within zeolite-Y cavity and also to the Ni(bpy)\(_{\mathrm {3}}^{\mathrm {2+ }}\)complex in contact with the phenosafranine dye co-adsorbed on the external surface of the host. Tris-(2,2′-bipyridine)-nickel(II)complex ion encapsulated zeolite-Y host has been synthesized via a ship-in-a-bottle method. Metal complexes and dye adsorptions were characterized by various spectroscopic methods. Photo-induced electron transfer between the surfaces adsorbed organic dye to encapsulated metal complexes have been investigated by picoseconds transient absorption spectroscopy.

CdIIMOFs Constructed Using Succinate and Bipyridyl Ligands: Photoluminescence and Heterogeneous Catalytic Activity

Four <TEX>$Cd^{II}$</TEX> MOFs, <TEX>$[Cd_2({\mu}-succinate)_2(H_2O)_2</TEX><TEX>]</TEX><TEX>{\cdot}H_2O$</TEX> (1A), <TEX>$[Cd_2({\mu}-succinate)_2({\mu}-4,4^{\prime}-bpy)_2</TEX><TEX>]</TEX><TEX>{\cdot}H_2O$</TEX> (1B), <TEX>$[\{Cd_2({\mu}-succinate)_2\}({\mu}-bpa)_2\{Cd(H_2O)_2\}(NO_3)_2</TEX><TEX>]</TEX><TEX>{\cdot}H_2O$</TEX> (2), and <TEX>$[Cd({\mu}-succinate)({\mu}-bpp)_2</TEX><TEX>]</TEX><TEX>{\cdot}2H_2O$</TEX> (3), with various bipyridyl ligands (4,4'-bipyridine (4,4'-bpy), 1,2-bis(4-pyridyl)ethane (bpa), and 1,3-bis(4-pyridyl)propane (bpp)) were prepared, and their structures were determined using X-ray crystallography. The structures and dimensionalities of <TEX>$Cd^{II}$</TEX>-(succinate) compounds varied depending on the auxiliary ligands. Heterogeneous catalytic activity for transesterification reactions, photoluminescence and the thermal stabilities of these compounds were also examined.

Electronic structure and spectroscopy of the cycloheptatrienyl molybdenum halide complexes [MoBrL2(η-C7H7)]n+ (L2 = 2CO, n = 0; L2 = 2,2′-bipyridyl, n = 0 or 1)

DFT calculations at the B3LYP/Def2-SVP level have been conducted on the half-sandwich cycloheptatrienyl molybdenum complexes [Mo(CO)3(η-C7H7)]+, [1]+ and [MoBrL2(η-C7H7)]n+ (L2=2 CO, n=0, 2; L2=bpy, n=0, 3; L2=bpy, n=1, [3]+; bpy=2,2′-bipyridyl). In all cases, strong δ-bonding interactions operate between the e2 level of the C7H7 ring and metal dxy and dx2-y2 orbitals resulting in a metal-centred HOMO with substantial dz2 character in the 18-electron, closed shell systems. The experimental electronic UV–Vis spectra of [1]+, 2 and 3 are accurately reproduced by TD-DFT methods. For complexes 2 and 3, assignments made with the assistance of calculated spectra indicate that absorptions in the region 390–770nm originate from a series of MLCT (metal–ligand charge transfer) or ILCT (inter-ligand charge transfer) transitions in which carbonyl, C7H7 and 2,2′-bipyridyl ligands act as acceptor systems from the metal or mixed metal and bromide donor groups. The metal-centred, one-electron oxidation of 3 to 3[PF6] results in almost complete quenching of the visible region MLCT/ILCT absorptions of 3 and replacement with weak transitions probably arising from bromide to metal LMCT (ligand to metal charge transfer) processes.

Bis(2,2'-bipyridyl-κ(2) N,N')chloridonickel(II) nitrate trihydrate.

In the title hydrated salt, [NiCl(C10H8N2)2](NO3)·3H2O, the Ni2+ ion is coordinated by two 2,2′-bipyridyl (2,2′-bpy) ligands and a chloride ion in a trigonal–bipyramidal geometry. The chloride ion occupies an equatorial site and the dihedral angle between the 2,2′-bpy ring systems is 72.02 (6)°. In the crystal, the components are linked by C—H⋯O and O—H⋯O hydrogen bonds and aromatic π–π stacking inter­actions [shortest centroid–centroid separation = 3.635 (2) Å], generating a three-dimensional network.

Synthesis of bifunctional Ru complexes with 1,2-dithiolane and carboxylate-substituted ligands

An N3-type, Ru heteroleptic complex, AK1, having one bipyridyl ligand modified with COOH groups for tethering to TiO2 and a second bipyridyl ligand modified with two lipoic acid units for binding to platinum, was synthesized. The photophysical and spectroelectrochemical properties were studied in solution, on TiO2, in a dye-sensitized solar cell and on a Pt wire electrode. The results showed that AK1 can produce a photocurrent on TiO2. Furthermore, AK1 binds to Pt via the lipoic acid ligand but not via the carboxylic acid group, and can be electrochemically addressed by the Pt via the lipoic acid linkage.

Theoretical Study of Reductive Functionalization of Methyl Ligands of Group 9 Complexes Supported by Two Bipyridyl Ligands: A Key Step in Catalytic Hydrocarbon Functionalization

A density functional theory (DFT) study was performed to understand the factors that control the reactivity of bipyridine (bpy)-ligated Rh(III) methyl complexes toward nucleophiles to produce functionalized methane and Rh(I) complexes. The effect of the structure of the complex, the nucleophile, the identity of the ancillary ligand, the electronic properties of the bipyridine ligand, and the identity of the metal were considered. Many similarities were found between the reaction of Rh(III) methyl complexes supported by bipyridyl ligands and classic organic SN2 reactions, including a strong dependence of the reaction on the nucleophile identity and modifications to the complex that facilitate rhodium as a leaving group. Using these concepts, a comparison of reductive functionalization of Rh(III) alkyl complexes supported by porphyrin versus two bipyridyl ligands was made, and modifications that could lead to more active complexes were proposed.

Soft ligand stabilized gold nanoparticles: Incorporation of bipyridyls and two-dimensional assembly

HypothesisThe synthesis of gold nanoparticles (AuNPs) in organic solvents without addition of surfactant may be achieved without the use of strong capping agents in the presence of soft ligands from the starting materials. Through post synthesis surface modification with ligands having moderate or strong affinity, the soft ligands should be displaced, allowing for manipulation of the AuNP size, size distribution, as well as the interparticle spacing. ExperimentsSynthesis of gold nanoparticles was undertaken using the reducing agent 9-borabicyclo[3.3.1]nonane without addition of stabilizing ligands. Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the NPs. The interparticle spacing in 2D assemblies of the NPs was correlated with localized surface plasmon resonance (LSPR) shifts exhibited by the NPs in solution. FindingsSoft-ligand-stabilized AuNPs in a size range of 3–5nm were generated at a slow rate. The soft ligands were found to be chloride (Cl−) ions and triethylphosphine (Et3P). Bipyridyl and thiol ligands displaced the weakly adsorbed soft ligands. Thiolate-stabilized AuNPs formed long range 2-D assemblies with regular interparticle spacing (edge-to-edge). UV–vis spectroscopy analysis shows the thiolated AuNPs exhibited an exponential localized wavelength (λmax) decay dependence on the alkylthiolate chain length, indicating an increase in the interparticle spacing.

ChemInform Abstract: Substituted 2,2′‐Bipyridines by Nickel Catalysis: 4,4′‐Di‐tert‐butyl‐2,2′‐bipyridine.

A simple, ligand-free synthesis of the important bipyridyl ligand 4,4′-di-tert-butyl-2,2′-bipyridine is presented. 5,5′-Bis(trifluoromethyl)-2,2′-bipyridine is also synthesized by the same protocol. The syntheses efficiently couple the parent 2-chloropyridines by a nickel-catalyzed dimerization with manganese powder as the terminal reductant.

Anionic Bipyridyl Ligands for Applications in Metallasupramolecular Chemistry

The facile synthesis of anionic bipyridyl ligands with dinuclear clathrochelate cores is described. These metalloligands can be obtained in high yields by the reactions of M(ClO4 )2 (H2 O)6 (M: Zn, Mn, or Co) with 4-pyridylboronic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-diformyl-4-tert-butylphenol oxime, followed by deprotonation. The ligands are interesting building blocks for metallasupramolecular chemistry, as evidenced by the formation of a Pt-based molecular square and four coordination polymers with 2D or 3D network structures. Competition experiments reveal that the utilization of anionic bipyridyl ligands can result in significantly more stable assemblies.

Effects of the π-conjugation length of bipyridyl ligand on the photophysical properties of binuclear organotin(IV) complexes: Synthesis and characterization of dimethyltin(IV) complexes with bipyridyl

The dimethyltin(IV) complexes of rigid bipyridyl-based ligands, 4,4′-bipyridine (4,4′-bipy) and 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (4-bpdb), were prepared and characterized by 1H, 13C and 119Sn NMR, IR, and UV spectroscopies, single-crystal X-ray diffraction and elemental analysis. The prepared complexes were used as green and yellow-orange electroluminescence dopant materials to fabricate organic light-emitting diodes (OLEDs) with a general configuration of ITO/PEDOT:PSS(90nm)/PVK:PBD:tin-complexes (80nm)/Al(200nm). The effects of long and rigid bipyridyl-based ligands on the electroluminescence properties of the complexes were investigated. The maximum emission peaks showed that a good correlation exists between the π-conjugation length of bipyridyl ligands and emission wavelength. Replacing 4-bpdb with the long π-conjugation length, 4,4′-bipy, resulted in red shifts in both absorption and fluorescence spectra and moderately enhanced the photoluminescence intensity and the fluorescence quantum yield. Furthermore, complex of dimethyltin(IV) with 4-bpdb ligand was doped into a PVK:PBD blend as the host in two different concentrations. It was found that the high concentration of dopant caused a trap effect in the current voltage and led to a self-quenching of emission and reduced the efficiency of the device.

Anion-Controlled Dielectric Behavior of Homochiral Tryptophan-Based Metal–Organic Frameworks

Three homochiral metal-tryptophanate frameworks, {[Zn2(l-trp)2(bpe)2(H2O)2]·2H2O·2NO3}n (1a, l-Htrp = l-tryptophan, bpe = 1,2-bis(4-pyridyl)ethylene), {[Co(l-trp)(bpe)(H2O)]·H2O·NO3}n (1b), and {[Co(l-trp)(bpa)(H2O)]·H2O·NO3}n (2, bpa = 1,2-bis(4-pyridyl)ethane), were constructed from Zn2+ or Co2+ ions, bipyridyl ligands, and the amino acid l-tryptophan (l-Htrp), respectively. Compounds 1a, 1b, and 2 were characterized by single-crystal X-ray diffraction analysis. All of the compounds crystallize in the monoclinic space group P21 and form homochiral two-dimensional (2D) layers with rectangle-like (4,4) topologies. Anion-controlled dielectric, luminescence, and nonlinear-optic (NLO) properties were measured for these chiral metal–organic frameworks (MOFs) in the solid state. Emission spectra confirmed that compound 1a exhibited a green emission at 546 nm. Dielectric studies of 1a revealed that it had very low dielectric constant (κ = 2.53 at 1 MHz), thus verifying that it is a promising candidate for inter...

Molecular Orbital Engineering of a Panchromatic Cyclometalated Ru(II) Dye for p-Type Dye-Sensitized Solar Cells

We report a panchromatic cyclometalated Ru(II) complex, denoted as O18, which shows intense metal-to-ligand charge transfer transitions in the visible to near-IR region with the absorption tail extending to 800 nm. The panchromatic spectra response and enhanced molar extinction coefficient (ε = 1.9 × 104 M–1 cm–1 at 593 nm in solution) of O18 are attributed to the stabilization of the lowest unoccupied molecular orbital and the increased absorption cross section via rationally extending the π-conjugated system of 2,2′-bipyridyl (bpy) ligands. As a result, NiO solar cells sensitized with O18 show short-circuit currents up to 3.43 mA cm–2 and efficiencies up to 0.104%, which are the best among all cyclometalated-Ru(II)-sensitized p-type dye-sensitized solar cells. Femtosecond transient absorption spectroscopy reveals decreased geminate recombination across the O18–NiO interface by 1 order of magnitude compared to our previous report.

Homochiral Silver-Based Coordination Polymers Exhibiting Temperature-Dependent Photoluminescence Behavior

Homochiral coordination polymers based on zigzag or helical polymers are assembled from a semiflexible fluorescent bipyridyl ligand and linear coordinated Ag(I) ions; they exhibit unusual temperature-dependent photoluminescence behavior, including multistep changes in energy and intensity upon cooling.