Intramolecular Energy Transfer Mechanism Research Articles

Enhanced Triplet Sensitizing Ability of an Iridium Complex by Intramolecular Energy-Transfer Mechanism.

The photodynamic properties involving both intra- and intermolecular triplet energy transfers (ET) of a bichromophoric photosensitizer having a tris-cyclometalated Ir(III) tethered with a pyrene derivative are studied. Due to the triplet energy gap of the two chromophores, a reversible intramolecular triplet ET equilibrium is quickly established upon photoexcitation, with the triplet exciton mainly residing on the acceptor side in the photostationary state. By virtue of the very small decay rate of triplet pyrene, a considerably extended triplet lifetime (2 ms) is observed. Next, the intermolecular triplet-triplet ET properties are investigated. Using steady-state and time-resolved spectroscopy, the ET rate constants from the Ir complex and pyrene unit in the sensitizer to an external triplet acceptor (unattached, free pyrene derivative) in solution are found to be around 109 s-1 and 108 M -1 s-1, respectively. In spite of a lower ET rate constant, the tethered pyrene serves as the main intermolecular ET channel because of the large, favorable intramolecular ET equilibrium ( K ∼ 103). Importantly, this cascade ET process, from Ir complex to linked pyrene, and then to free pyrene, offers an overall improved ET efficiency than a direct ET from Ir complex to free pyrene, by virtue of the much smaller spontaneous decay rate compared to that of the metal complex. Finally, the more efficient ET ability is demonstrated experimentally by applying the molecule as sensitizer in a triplet-triplet annihilation upconversion. The bichromophoric sensitizer achieved upconverted emission intensity 5 times higher than a monochromophoric Ir-complex analogue.

Rare Earth-Indomethacinate Complexes with Heterocyclic Ligands: Synthesis and Photoluminescence Properties

In this work, synthesis, characterization and photophysical properties of trivalent rare earth complexes with a nonsteroidal anti-inflammatory drug [the indomethacinate (indo), presenting formulas RE(indo)3(H2O)x (x = 3, for Eu3+ and Gd+3, and x = 4 for Tb+3), RE(indo)3(bipy) and RE(indo)3(phen) (bipy: 2,2'-bipyridine, and phen: 1,10-phenanthroline)] were investigated. Based on photoluminescent results, the intramolecular energy transfer process from T1 triplet states of indo, phen and bipy ligands to the 5D0 emitting level of the Eu3+ ion in the coordination compounds is discussed. Accordingly, it is proposed two possible intramolecular energy transfer mechanisms between indomethacinate ligand and rare earth ions, which involve the participation of excited electronic states of the heterocyclic ligands as intermediate ones.

A highly selective fluorescent chemosensor for Cu2+ : synthesis and properties of a rhodamine B-containing diarylethene.

A diarylethene bearing a triazole-linked rhodamine B unit was synthesized. Its fluorescent emission was significantly enhanced in the presence of protons or Cu2+ due to transformation from the pirocyclic form to open-ring form. The fluorescence was quenched sequentially upon irradiation with 297nm light based on the intramolecular fluorescence resonance energy transfer mechanism. In an acetonitrile: water binary solvent (1: 1v/v), the compound showed significant fluorescent enhancement for Cu2+ compared with a wide range of tested metal ions with a fast response and a limit of detection of 2.86×10-8 molL-1 . Using Cu2+ and UV light as the chemical inputs, and fluorescence intensity at 597nm as the output, a logic gate was developed at the molecular level. Moreover, the compound can be used with a high accuracy to detect Cu2+ in a natural water sample.

Synthesis, photoluminescence features with intramolecular energy transfer and Judd–Ofelt analysis of highly efficient europium(III) complexes

The luminescent binary and ternary europium(III) complexes were prepared by employing ethyl-(3-fluorobenzoyl) acetate (m-EFBA) as primary ligand and neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy) as secondary ligands. The synthesized complexes Eu(m-EFBA)3·(H2O)2 (C1), Eu(m-EFBA)3·neo (C2), Eu(m-EFBA)3·batho (C3), Eu(m-EFBA)3·phen (C4), Eu(m-EFBA)3·bipy (C5) were characterized by the means of elemental analysis (C, H and N), nuclear magnetic resonance spectroscopy (1H-NMR), infrared spectroscopy (IR), thermogravimetric analysis (TG/DTG), UV–visible and photoluminescence (PL) spectroscopy. The photoluminescence spectra of complexes exhibit the characteristic emission band at 613 nm assigned to hypersensitive 5D0 → 7F2 transition, responsible for the red color emission of complexes. The higher photoluminescence intensity of ternary europium(III) complexes C2–C5 as compared to binary complex C1, suggest that ancillary ligands neo, batho, phen and bipy enhance the process of sensitization from ligand (m-EFBA) to europium(III) ion. The luminescence decay time and quantum efficiencies of the complexes were determined to estimate the efficiency of energy transfer from ligand to metal ion. In addition, the Judd–Ofelt intensity parameters (Ω2, Ω4) were calculated from the emission intensities of 5D0 → 7F2 and 5D0 → 7F4 transitions of europium(III) ion respectively. The intramolecular energy transfer mechanism of the complexes were also investigated and results indicate that the ligand (m-EFBA) and ancillary ligands effectively transfer the energy to that of Eu(III) ion.

Synthesis, NMR, photoluminescence studies and intramolecular energy transfer process of europium(III) complexes

Abstract The studies related to the synthesis and luminescence properties of five europium(III) complexes of the type [Eu(OFHD)L] where OFHD is deprotonated 1,1,1,5,5,6,6,6-octafluorohexane-2,4-dione and L is H 2 O ( C1 ), 2,2′-biquinoline ( C2 ), neocuproine ( C3 ), 1,10-phenanthroline ( C4 ) and 2,2′- bipyridyl ( C5 ) are reported in the present communication. The synthesized complexes were investigated by means of elemental analysis, IR, 1 H NMR, UV–vis spectroscopy and TGA techniques. The high fluorination in the complexes makes them best candidates of NMR shift reagents to resolve the spectra as revealed in 1 H NMR study. The excitation and emission spectra of complexes in solid state were investigated in detail. Further, on the basis of emission spectra, the CIE color coordinates (x and y), luminescence decay time (τ), radiative decay rate (A rad ), nonradiative rate (A nrad ), quantum efficiency (η) and Judd-Ofelt intensity parameter (Ω 2 ) were calculated and analyzed. The interaction of lowest triplet levels of ligands with the emitting levels of europium(III) ion is represented by proposed intramolecular energy transfer mechanism. The beauty of these complexes is that they can be used as NMR shift reagents and are of particular interest in the field of light emitting materials.

Synthesis and aggregation-induced emission enhancement of naphthalimide-rhodamine dye

Abstract A series of naphthalimide-rhodamine dye L1–4 with the different terminal structures were designed and synthesized. The rhodamine was used as bulky rigid substituent of naphthalimide to enhance the AIE property. All the naphthalimide-rhodamine dye exhibited the significant aggregation-induced emission enhancement. The strong fluorescence emissions in solid state were observed with emission peaks ranging from 549 to 608 nm. In high fW mixture solution, the fluorescence intensity enhanced with the increase of water content, which can be attributed to two types of aggregation-induced morphology. The AIE dye-doped silica nanoparticles (Si-NPs) were prepared and exhibited good solubility in pure water. In addition, dye L1 and L2 exhibited the selective recognition toward Hg2+ ions and were successfully applied to the bioimages in living cells. The intramolecular fluorescence resonance energy transfer mechanism from the naphthalimide moiety to the rhodamine moiety was investigated.

Investigations of luminescent behavior and intramolecular energy transfer mechanism of europium(III) complexes with fluorinated β-ketoester ligand

Abstract A fluorinated β-ketoester ligand, ethyl-(2-fluorobenzoyl) acetate (EFBA) has been employed to synthesized new europium binary and ternary complexes with ancillary ligands neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy) in high yield by the solution precipitation method. The ligand (EFBA) and the synthesized complexes Eu(EFBA) 3 ·(H 2 O) 2 (C1), Eu(EFBA) 3 ·neo (C2), Eu(EFBA) 3 ·batho (C3), Eu(EFBA) 3 ·phen (C4), Eu(EFBA) 3 ·bipy (C5) were characterized by elemental analysis, 1 H NMR, IR, UV–vis, thermal analysis (TG/DTG) and luminescence spectroscopy. The thermal analysis results show that the complex is stable up to 231 °C temperature which is sufficient for the normal working of OLEDs. The luminescence measurements indicate that π electron rich organic ligand ethyl-(2-fluorobenzoyl) acetate possessing high absorption coefficient acts as a suitable chromophoric moiety for the transfer of energy to the central Eu 3+ ion by the process of sensitization, this results in strong emissions band in red spectral region attributed to electric dipole 5 D 0 → 7 F 2 transition of europium ion. The luminescence intensity further enhanced by the introduction of N-containing ancillary ligands neocuproine, bathophenanthroline, 1,10-phenanthroline, and 2,2-bipyridyl in the ternary complexes C2–C5 because these ligands replace the solvent molecule in the coordination sphere and satisfy the coordination number around central europium ion. The sensitization process in europium complexes is investigated through the proposed energy transfer mechanism. The decay curves observations show the similar chemical environment around the europium ion in all the complexes.

FRET-based rhodamine–coumarin conjugate as a Fe3+ selective ratiometric fluorescent sensor in aqueous media

In this study, a novel ratiometric fluorescent sensor (HL) for Fe3+ based on the conjugation of rhodamine and coumarin has been designed and synthesized. The free sensor displays fluorescence emission at 475nm, on the addition of Fe3+ to an aqueous solution of HL, the sensor shows significant fluorescence enhancement at 550nm which should be attributed to an intramolecular fluorescence resonance energy transfer (FRET) mechanism from coumarin to Rhodamine 6G.

Synthesis, photoluminescent features and intramolecular energy transfer mechanism of europium (III) complexes with fluorinate β-diketone ligand and auxiliary ligands

Abstract A series of novel luminescent europium (III) complexes based on fluorinated β-diketone ligand 4,4-difluoro-1-phenyl-1,3-butanedione (DPBD) and auxiliary ligands 2,2-biquinoline (biq) or 1,10-phenanthroline (phen) or neocuproine (neo) or 2,2-bipyridyl (bipy) have been synthesized. The ligand DPBD with their complexes Eu(DPBD)3·(H2O)2 (C1), Eu(DPBD)3·biq (C2), Eu(DPBD)3·phen (C3), Eu(DPBD)3·neo (C4) and Eu(DPBD)3·bipy (C5) were confirmed by elemental analysis, infrared (IR) and proton nuclear magnetic resonance (NMR) spectroscopy. The crystalline nature, photoluminescence and thermal behavior were investigated by powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and TG/DTA-DSC respectively. The emission spectra of complexes showed the characteristics sharp bands in solid state corresponding to 5D0–7Fj (j = 0–3) transition of europium ion with 5D0–7F2 as the most intense transition. The emission spectra, energy transfer mechanism, luminescence decay time and relative quantum efficiency clearly reveals that these photophysical properties are greatly influenced by the π-conjugated system, stability of the complexes and the efficient energy transfer from DPBD ligand to emitting level of Eu3+ ion. The complex Eu(DPBD)3·bipy (C5) exhibited highest quantum efficiency, luminescence intensity bearing good CIE color coordinates (x = 0.64 and y = 0.34) matching the NTSC (National Television Standard Committee) standard values for the pure red color and longest lifetime which makes it a promising red-emitting component for display devices.

Theoretical analysis of excited states and energy transfer mechanism in conjugated dendrimers.

The excited states of the phenylene ethynylene dendrimer are investigated comprehensively by various electronic-structure methods. Several computational methods, including SCS-ADC(2), TDHF, TDDFT with different functionals (B3LYP, BH&HLYP, CAM-B3LYP), and DFT/MRCI, are applied in systematic calculations. The theoretical approach based on the one-electron transition density matrix is used to understand the electronic characters of excited states, particularly the contributions of local excitations and charge-transfer excitations within all interacting conjugated branches. Furthermore, the potential energy curves of low-lying electronic states as the functions of ethynylene bonds are constructed at different theoretical levels. This work provides us theoretical insights on the intramolecular excited-state energy transfer mechanism of the dendrimers at the state-of-the-art electronic-structure theories.

Eu(III) and Tb(III) Complexes with the Nonsteroidal Anti-Inflammatory Drug Carprofen: Synthesis, Crystal Structure, and Photophysical Properties

Two new lanthanide complexes with general formula [Ln2(carprofen)6(DMF)2] (Ln = Eu (1), Tb (2), DMF = N,N-dimethylformamide, carprofen = 6-chloro-α-methylcarbazole-2-acetic acid) have been synthesized by a hydrothermal method. Complex 1 was characterized by single-crystal X-ray diffraction (XRD), and it was found to crystallize in the monoclinic space group C2/c. The coordination of the ligand to the lanthanide ion has been investigated by Fourier-transform infrared (FTIR) spectra and ultraviolet-visible (UV-vis) absorption spectra. Complex 1 emits red light, but the antenna effect of the ligand is not effective, whereas complex 2 presents intense green emission with effective energy transfer from the ligand. The different performance of the two complexes is related to the energy matching between the excited states of the lanthanide ion and the triplet state of the ligand. The intramolecular energy transfer mechanisms are also discussed.

Heterodinuclear (Sm, Tb) lanthanide pivalates with heterocyclic N-donors: synthesis, structure, thermal behavior, and magnetic and photoluminescence properties.

Heterobimetallic complexes [SmTb(piv)6(phen)2] (1), [SmTb(piv)6(bath)2]·1.75EtOH (2a·1.75EtOH), [SmTb(piv)6(bath)2]·2EtOH (2b·2EtOH), and [SmTb(piv)6(bath)2]·EtOH (2b·EtOH), where piv is (CH3)3CCO2(-), phen is 1,10-phenanthroline, and bath is 4,7-diphenyl-1,10-phenanthroline, were synthesized and studied by X-ray diffraction. It was shown that complexes 2a·1.75EtOH and 2b·2EtOH have different molecular and crystal structures. Complexes 2a·1.75EtOH, 2b·2EtOH, and 2b·EtOH differ in the structural functions of μ2-piv anions. 2a·1.75EtOH contains two μ2-piv-κ(2)O,O' anions and two μ2-piv-κ(2)O,O,O' anions, whereas 2b·2EtOH and 2b·EtOH have four μ2-piv-κ(2)O,O' anions. According to the mass spectrometry data, the dimeric molecule [SmTb(piv)6] is the major metal-containing component of gas-phase complexes 1, 2a·1.75EtOH, and 2b·2EtOH. The characteristic features of the thermal behavior of these complexes were revealed, and their magnetic and photoluminescence (PL) properties were investigated. A unique feature of desolvated complexes 2a·1.75EtOH and 2b·2EtOH is melting at high temperatures before thermal decomposition. The magnetic properties of 1 and 2a·1.75EtOH are determined mainly by the Tb(3+) ions. The optical properties of these complexes and their homodinuclear analogs were analyzed by photoluminescence, excitation, phosphorescence, and scattering spectroscopy and by lifetime measurements at 77 K and 300 K. As the temperature decreases to 77 K, the PL intensity of Tb(3+) ions in 1 and 2a·1.75EtOH substantially increases by 40 and 100 times, respectively, compared to 300 K. The PL color evidently changes from red at 300 K to bright green at 77 K. Based on these results, the mechanism of intramolecular energy transfer between the ligand levels and Sm(3+) and Tb(3+) ions under UV radiation was proposed.

Photoluminescence studies of a Terbium(III) complex as a fluorescent probe for DNA detection

The photoluminescence properties of a Tb(III) complex of the form [Tb(phen)2Cl3·OH2] (phen=1,10-phenanthroline) in different solvents are presented. It shows the characteristic luminescence of the corresponding Ln3+ ion in the visible region. The emission intensity of this complex in coordinating solvent is higher than non-coordinating one. The suggested mechanism for the energy transfer between the ligand and Tb3+ ion is the intramolecular energy transfer mechanism. The interactions of the Tb(III) complex with fish salmon DNA are studied by fluorescence spectroscopy, circular dichroism study and viscosity measurements. The results of fluorescence titration reveal that DNA strongly quenches the intrinsic fluorescence of the complex through a static quenching procedure. The binding constant (Kb) of the above metal complex at 25°C is determined by the fluorescence titration method and it is found to be (8.06±0.01)×103M−1. The thermodynamic parameters (ΔH0>0, ΔS0>0 and ΔG0<0) indicate that the hydrophobic interactions play a major role in DNA–Tb complex association. The results support the claim that the title complex bonds to FS-DNA by a groove mode.

Synthesis, characteristic and intramolecular energy transfer mechanism of reactive terbium complex in white light emitting diode

A reactive Tb(III) complex with 2-aminobenzoic acid (2-ABAH) and acrylonitrile (AN) as ligands was synthesized. The structure of the complex was characterized by elemental analysis and Fourier transform infrared spectrometry (FT-IR). The results indicated that the ligands were coordinated with Tb(III) ion. Thermal gravity-derivative thermogravimetric (TG-DTG) analysis indicated that the complex kept stable up to 198 °C. Luminescence properties were investigated by UV-vis absorption spectra and fluorescence spectra. The results suggested that being excited at 361 nm, the complex exhibited characteristic emission of Tb(III) ion, revealing that the complex could be excited by 365 nm ultraviolet chip. The HOMO and LUMO, ΔE(HOMO–LUMO), molecular frontier orbital, and the singlet state and triplet energy state levels of the ligands were calculated at the B3LYP/6-31+G (d) level. The results indicated that intramolecular energy transfer mechanism followed Dexter exchange energy transfer theory. Both the calculation for excited state of ligand and energy transfer mechanism could provide the theoretical basis for the design of high luminescent materials of rare earth complexes with organic ligands.

The synthesis, photoluminescence and energy transfer mechanism of a reactive Eu(III)-complex intermediate of white light phosphor

A reactive Eu(III)-complex intermediate of white light phosphor was synthesized using benzoylactone, 1,10-phenanthroline and undecylenic acid as ligands. The structure of the complex was characterized by elemental analysis and FT-IR spectra. The luminescent properties were investigated by fluorescence spectra and UV–vis absorption spectra. The results indicate that the complex emitted the characteristic peaks of the Eu(III) ion when being excited at 367 nm, revealing that the complex can be excited by 365 nm of ultraviolet. The energy of the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as the singlet state and triplet state energy level of the ligands were calculated with the Gaussian03 program package. Intramolecular energy transfer mechanism was studied and an energy transfer diagram was sketched to illuminate the energy transfer process. The Eu(III)-copolymer was synthesized by the free radical copolymerization of the Eu(III)-complex and methyl methacrylate. XRD analysis indicates that the Eu(III)-complex in the copolymer was dispersed much more uniformly into the polymer matrix than that in the doped polymer. The photoluminescent properties of the Eu(III)-polymer suggest that the Eu(III)-complex is a good candidate of red light moiety in white light phosphor.

Simultaneous Intracellular β-d-Glucosidase and Phosphodiesterase I Activities Measurements Based on A Triple-Signaling Fluorescent Probe

Despite that considerable efforts have been devoted to the design of various fluorogenic enzyme substrates, they are single-enzyme assay approaches that cannot afford detection of multienzyme activity. In this study, we set out our first attempt to design a new probe that could measure intracellular β-D-glucosidase and phosphodiesterase I activities. Unlike the commonly used fluorogenic enzyme substrates that contain one recognition site and signaling reporter, the new probe molecule possesses two cleavage sites, specificly corresponding to β-D-glucosidase and phosphodiesterase I, and three fluorescent reporters, 7-β-D-glucopyranosyloxycoumarin, 7-hydroxycoumarin, and meso-tetraphenylporphyrin. On the basis of intramolecular photoinduced electron transfer and fluorescence resonance energy transfer mechanisms, interaction of the probe with the two enzymes, whether only one or both, produces different signal readouts with high sensitivity. Remarkably, the probe is chemically stable in complex biological fluids. Fluorescence outputs are not significantly affected by biologically related metal ions, anions, amino acids, and proteins. Furthermore, fluorescence microscopy confirmed that the probe is an excellent candidate for intracellular delivery and can be accumulated intensively in cells. We demonstrated the applicability for the simultaneous images of intracellular β-D-glucosidase and phosphodiesterase I activities using the different optical imaging modes.

Benzene ring impact on energy transfer system of Eu(TTA) 3DPBT

Eu(TTA) 3DPBT was found most likely to lead a special singlet photosensitization pathway by means of time-resolved luminescence spectroscopic studies. For further understanding of its intra-molecular energy transfer mechanism, another lanthanide complex Eu(TTA) 3BDDT was synthesized, using a related ligand BDDT, changing the D-p-A structure of DPBT to the D-A structure of BDDT. The luminescence characteristics of both complexes were investigated and compared. Results show that p bridge plays an important role in the energy transfer process. p bridge can change the charge separation strength by affecting the electron-density distribution over the diethylaniline and the dipyrazoletriazine moieties. Without the p bridge connection, the benzene ring, BDDT gets a smaller conjugated system, and the absorption peak in the UV-Vis spectrum of BDDT has a blue shift of 114 nm relative to that of DPBT. So the energy level of ligand BDDT and the central ion Eu(III) does not match well, and the energy transfer efficiency drop 33%.

Theoretical Investigation of the Mechanism and Dynamics of Intramolecular Coherent Resonance Energy Transfer in Soft Molecules: A Case Study of Dithia-anthracenophane

A computational study is conducted on dithia-anthracenophane (DTA), for which there is experimental evidence for coherent resonance energy transfer dynamics, and on dimethylanthracene (DMA), a molecule representing the energy donor and the acceptor in DTA. Electronic excitation energies are calculated by configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) methods and are compared to experimental ones. Electronic coupling constants are calculated between two DMAs embedded into the ground-state structure of DTA employing methods based on transition densities. The resulting values of electronic coupling provide a more consistent interpretation of experiments than those based on one-half the level spacing of DTA excitation energies. Solvation effects are studied based on the polarizable continuum model (PCM). Solvent-induced polarization and screening effects are shown to make opposite contributions, and the net electronic coupling is little different from the value in a vacuum. The likelihood of coherent population transfer is assessed on the basis of a recently developed theory of coherent resonance energy transfer. The time scale of bath is shown to have an important role in sustaining the quantum coherence. The combination of quantum chemical and dynamical data suggests that the electronic coupling in DTA is in the range of 50-100 cm(-1). The presence of oscillatory excitation population dynamics can be understood from the picture of polaronic excitation moderately dressed with dispersive vibrational modes. The effect of torsional modulation on the excitation energies of DTA and electronic coupling is examined on the basis of optimized structures with the torsional angle constrained. The result suggests that inelastic effect due to torsional motion cannot be disregarded in DTA.

Efficient Fluorescence Resonance Energy Transfer-Based Ratiometric Fluorescent Cellular Imaging Probe for Zn2+ Using a Rhodamine Spirolactam as a Trigger

This letter described the design and synthesis of a novel fluorescein-appended rhodamine spirolactam derivative and its preliminary application as a ratiometric fluorescent cellular imaging probe for Zn(2+). The ratiometric fluorescent signal change of the probe is based on an intramolecular fluorescence resonance energy transfer (FRET) mechanism modulated by a specific metal ion induced ring-opening process of the rhodamine spirolactam (acting as a trigger). In the new developed sensing system, the emission peaks of the two fluorophores are well-resolved, which can avoid the emission spectra overlap problem generally met by spectra-shift type probes and benefits for observation of fluorescence signal change at two different emission wavelengths with high resolution. It also benefits for a large range of emission ratios, thereby a high sensitivity for Zn(2+)detection. Under optimized experimental conditions, the probe exhibits a stable response for Zn(2+) over a concentration range from 2.0 x 10(-7) to 2.0 x 10(-5) M, with a detection limit of 4.0 x 10(-8) M. Most importantly, the novel probe has well solved the problem of serious interferences from other transition metal ions generally met by previously reported typical fluorescent probes for Zn(2+) with the di(2-picolyl)amine moiety as the receptor (in this case, the fluorescence response induced by Cd(2+)is even comparable to that of Zn(2+)) and shows a reversible and fast response toward Zn(2+). All these unique features make it particularly favorable for ratiometric cellular imaging investigations. It has been preliminarily used for ratiometric imaging of Zn(2+) in living cells with satisfying resolution.

Emission Enhancement through Dual Donor Sensitization: Modulation of Structural and Spectroscopic Properties in a Series of Europium Tetracyanoplatinates

The synthesis of three different europium tetracyanoplatinates all incorporating 2,2':6',2''-terpyridine (terpy) have been carried out in acetonitrile/water mixtures by reaction of Eu(3+) salts with terpy and potassium tetracyanoplatinate. The use of different Eu(3+) sources results in the isolation of Eu(C(15)H(11)N(3))(H(2)O)(2)(NO(3))(Pt(CN)(4)) x CH(3)CN (1), {Eu(C(15)H(11)N(3))(H(2)O)(3)}(2)(Pt(CN)(4))(3) x 2 H(2)O (2), or [Eu(C(15)H(11)N(3))(H(2)O)(2)(CH(3)COO)(2)](2)Pt(CN)(4) x 3 H(2)O (3) for the nitrate, triflate, or acetate salts, respectively. All three compounds have been prepared as colorless crystals, and single-crystal X-ray diffraction has been used to investigate their structural features. Crystallographic data (MoK alpha, lambda = 0.71073 A, T = 290 K): 1, monoclinic, space group P2(1)/c, a = 12.835(1), b = 15.239(1), c = 13.751(2) A, beta = 105.594(9) degrees, V = 2590.8(5) A(3), Z = 4; 2, triclinic, space group P1, a = 9.1802(8) A, b = 10.8008(9) A, c = 13.5437(9) A, alpha = 84.491(6) degrees, beta = 75.063(7) degrees, gamma = 79.055(7) degrees, V = 1272.4(2) A(3), Z = 1; 3, triclinic, space group P1, a = 12.110(3) A, b = 12.7273(11) A, c = 18.7054(16) A, alpha = 92.859(7) degrees, beta = 92.200(11) degrees, gamma = 118.057(10) degrees, V = 2534.8(7) A(3), Z = 2. Variation of the counteranions in these systems provides the opportunity to modify the structures and coordination environment of Eu(3+) for 1-3. Compounds 1 and 2 are both one-dimensional, polymeric compounds that contain Eu(3+) ions chelated by terpy and bridged by tetracyanoplatinate anions. 3 is a zero-dimensional complex salt in which Eu(3+) is coordinated by terpy, acetate, and water, but not tetracyanoplatinate. The structural differences result in varying sensitization phenomena for the three compounds. Compounds 1 and 2 display efficient donor-acceptor intramolecular energy transfer (IET) where dual donor species, terpyridine and tetracyanoplatinate, simultaneously enhance the acceptor Eu(3+) emission. In both compounds the donor species are directly coordinated to the acceptor ion, and hence a highly efficient dual-donor effect is exhibited for the IET mechanisms. In 3 where only the terpy ligand is directly coordinated to Eu(3+), the sensitization involves only one donor species. The Pt(CN)(4)(2-) unit in 3, which lacks direct bonding to Eu(3+), exhibits strong emission indicating the lack of cooperative enhancement of the lanthanide emission.