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Energy-transfer Process (energy-transfer + process)
Selected AbstractsMechanism of excitation and relaxation in Er,O-codoped GaAs for 1.5 ,m light-emitting devices with extremely stable wavelengthPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008Yasufumi Fujiwara Abstract Energy-transfer processes in Er,O-codoped GaAs (GaAs:Er,O) have been investigated by means of a pump and probe reflection technique. Time-resolved reflectivity exhibited a characteristic dip; a negative signal due to bandgap renormalization in less than 1 ps and then a gradual recovery. In the recovery process, there were two components, fast and slow. The fast recovery time (several ps) was inversely proportional to Er concentration. The analysis based on a rate equation indicated that it is due to the capture of electrons by charged traps. The slow recovery (30,60 ps) was well coincident with the time (54 ps) predicted theoretically in the framework of a multiphonon-assisted model. Optical excitation cross section of Er ions in GaAs:Er,O has also been studied in various samples and shown to depend strongly on Er concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Close Proximity Dibenzo[a,c]phenazine,Fullerene Dyad: Synthesis and Photoinduced Singlet Energy TransferEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2010Rajeev K. Dubey Abstract A dibenzo[a,c]phenazine,fullerene (DBPZ-C60) dyad in which two chromophores are linked in close proximity to each other has been synthesized and studied in detail by optical spectroscopy to explore a new energy donor,acceptor system. The dyad was prepared by Prato reaction between 11-formyldibenzo[a,c]phenazine and fullerene. 3,5-Di- tert -butylbenzyl group was introduced onto the fulleropyrrolidine unit to achieve adequate solubility of the dyad. A thorough study of the photophysical properties of the dyad and relevant reference compounds, performed by means of steady state and time resolved spectroscopic measurements, has revealed the presence of highly efficient (ca. 98,%) and extremely fast (ken = 5,×,1011 s,1) intramolecular photoinduced singlet,singlet energy-transfer process from singlet excited state of the DBPZ moiety to fullerene. In both polar and nonpolar environment transduction of singlet excited state energy governs the excited state deactivation, but the efficiency and rate of energy transfer were found to be higher in nonpolar solvents in comparison to polar. The DBPZ singlet excited state decays within 2 and 4.7 ps in toluene andbenzonitrile, respectively, via singlet,singlet energy transfer to produce a fullerene singlet excited state which decays with a life time of 1.5 ns to give a very long-lived fullerene triplet state as final populated excited state. [source] Energy- and Charge-Transfer Processes in a Perylene,BODIPY,Pyridine Tripartite ArrayEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2008Mohammed A. H. Alamiry Abstract A novel boron dipyrromethene (BODIPY) dye has been synthesized in which the F atoms, usually bound to the boron center, have been replaced with 1-ethynylperylene units and a 4-pyridine residue is attached at the meso -position. The perylene units function as photon collectors over the wavelength range from 350 to 480 nm. Despite an unfavorable spectral overlap integral, rapid energy transfer takes place from the singlet-excited state of the perylene unit to the adjacent BODIPY residue, which is itself strongly fluorescent. The mean energy-transfer time is 7,±,2 ps at room temperature. The dominant mechanism for the energy-transfer process is Dexter-type electron exchange, with Förster-type dipole,dipole interactions accounting for less than 10,% of the total transfer probability. There are no indications for light-induced electron transfer in this system, although there is evidence for a nonradiative decay channel not normally seen for F -type BODIPY dyes. This new escape route is further exposed by the application of high pressure. The meso -pyridine group is a passive bystander until protons are added to the system. Then, protonation of the pyridine N atom leads to complete extinction of fluorescence from the BODIPY dye and slight recovery of fluorescence from the perylene units. Quenching of BODIPY-based fluorescence is due to charge-transfer to the pyridinium unit whereas the re-appearance of perylene-based emission is caused by a reduction in the Förster overlap integral upon protonation. Other cations, most notably zinc(II) ions, bind to the pyridine N-atom and induce similar effects but the resultant conjugate is weakly fluorescent.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis and Characterization of Carbazole-Based Dendrimers with Porphyrin CoresEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Ting Hua Xu Abstract A series of novel dendritic carbazole-based porphyrins [T(Cz-Gn)Ps] have been synthesized by a combination of Ullmann coupling and Adler condensation reactions and their intramolecular energy-transfer properties have been studied by absorption and steady-state fluorescence spectroscopy. It has been found that the light-harvesting capabilities of T(Cz-Gn)Ps increase with increasing generation, but that the efficiency of the energy transfer decreases from T(Cz-G0)P to T(Cz-G2)P due to the Förster energy-transfer process. In addition, these dendritic macromolecules can emit intense red light with high fluorescence quantum yields and so may find applications in photonic devices. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] A Mechanically Interlocked [3]Rotaxane as a Light-Harvesting Antenna: Synthesis, Characterization, and Intramolecular Energy TransferCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Jie-Yu Wang Abstract Mimicking photosynthesis: The concept of light-harvesting by using a mechanically interlocked [3]rotaxane is developed through synthesis and characterization. Our results provide a new candidate for light-harvesting systems and also open up the possibility of creating intelligent or controllable energy-collecting machines (see figure). A mechanically interlocked light-harvesting system [3]rotaxane A has been synthesized in high yield through Cu(I)-catalyzed azide,alkyne cycloaddition; the hexyl-substituted truxene units are introduced into the wheels as donors and an oligo(para -phenylenevinylene) (OPV) unit into the axis as the acceptor. The structure and the purity of [3]rotaxane A were confirmed by 1H and 13C,NMR spectroscopy and ESI HRMS. The azide,alkyne cycloaddition is demonstrated to be an efficient stoppering method in the synthesis of the rotaxane containing dibenzo[24]crown-8 and dibenzyl ammonium units. Detailed steady-state UV/Vis absorption, photoluminescent, and time-resolved fluorescence spectroscopy were performed to investigate the photophysical properties of [3]rotaxane A and its reference compounds in solution and as thin films. Even in dilute solution, efficient energy transfer from the truxene-functionalized wheels to the OPV-based axis, through the dibenzo[24]crown-8 and dibenzyl ammonium interaction, is observed in [3]rotaxane A. The unique topology of [3]rotaxane A not only efficiently promotes the intramolecular energy-transfer process, but also prevents intermolecular aggregation in the solid state. The new antenna system opens up the possibility of controllable light-harvesting molecular machines or other optoelectronic devices on the nanometer scale. [source] Triplet MLCT Photosensitization of the Ring-Closing Reaction of Diarylethenes by Design and Synthesis of a Photochromic Rhenium(I) Complex of a Diarylethene-Containing 1,10-Phenanthroline LigandCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2006Chi-Chiu Ko Dr. Abstract Synthesis of the diarylethene-containing ligand L1 based on Suzuki cross-coupling reaction between thienyl boronic acid and the dibromophenanthroline ligand is reported. On coordination to the rhenium(I) tricarbonyl complex system, the photochromism of L1 could be photosensitized and consequently extended from intraligand excitation at ,,340 nm in the free ligand to metal-to-ligand charge-transfer (MLCT) excitation at ,,480 nm in the complex. The photochromic reactions were studied by 1H NMR, UV/Vis, and steady-state emission spectroscopy. Photosensitization was further probed by ultrafast transient absorption and time-resolved emission spectroscopy. The results provided direct evidence that the formation of the closed form by the MLCT-sensitized photochromic process was derived from the 3MLCT excited state. This supports the photosensitization mechanism, which involves an intramolecular energy-transfer process from the 3MLCT to the 3IL(L1) state that initiated the ring-closure reaction. The photophysical and electrochemical properties of the complex were also investigated. [source] Dynamic Chemical Devices: Photoinduced Electron Transfer and Its Ion-Triggered Switching in Nanomechanical Butterfly-Type Bis(porphyrin)terpyridines,CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006Myriam Linke-Schaetzel Dr. Abstract A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (,,,)-diamine substrates to the ZnII,porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the ,3 -terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs. Une série d'architectures moléculaires, présentant une forme de papillon, a été préparée avec de bons rendements en utilisant une méthodologie synthétique comprenant comme étape clé un double couplage de Stille. Ces architectures sont composées d'un squelette terpyridine (terpy), qui compose le torse du papillon, sur lequel deux ailes porphyriniques ont été greffées; la géométrie peut varier entre une conformation étendue en forme de W, et une conformation compacte en forme de U, dû à la complexation du torse terpy par un cation de taille et coordination adéquate. Les ailes porphyriniques se présentent soit comme bases libres ou, peuvent être métallées successivement avec différentes métaux, pouvant ainsi avoir différentes "couleurs". Des études de fluorescence non seulement stationnaire mais aussi résolues dans le temps sur les architectures HZn, ZnAu et Zn2Au, montrent que les propriétés électroniques sont très dépendantes de la géométrie adoptée. Dans la conformation W étendue, nous avons mis en évidence un processus de transfert d'énergie de la porphyrine base libre vers la porphyrine metalée avec du Zn. Dans la conformation U de Zn2Au la luminescence de l'aile donneuse, à cause de l'état excité singulet, est fortement éteinte, non seulement à cause de l'effet d'atome lourd, mais aussi à cause d'un processus de transfert d'électron vers l'état fondamental de l'aile metalée avec de l'or. De plus, par compléxation avec des (,,,)-diamines des atomes de ZnIIdans les tetrapyrroles porphyrinques, la conformation induite du système peut être profondément influencée. Pour le composé Zn2Zn, que nous avons pu obtenir en monocristaux, des expériences de diffraction en utilisant comme source lumineuse un synchrotron, ont fourni des données qui ont permis de résoudre la structure par des méthodes directes et de la raffiner pour montrer la conformation en U attendue. L'atome central de Zn a une coordination de six dont trois provenant du ligand ,3 -terpy, et les autres de deux anions acetates, un monodenté et l'autre semi-chelatizé. La structure est ligotée par des multiples liaisons hydrogène entre des ligands aqueux sur les atomes de Zn externes et les atomes d'oxygène des anions acetates. Le système présenté est un double effecteur qui montre une commutation opto-mechanique dirigée soit par des ions métalliques, soit par d'autres ligands de taille adaptée. En même temps, les processus de transfert d'énergie et d'électrons peuvent être commuté en laissant de la place pour améliorer le rapport "on/off" dans de futures architectures. Abstract in Romanian:O serie de arhitecturi moleculare având o form, de fluture au fost preparate cu randamente bune utilizând o metodologie sintetic, cuprinzând ca etap, cheie un dublu cuplaj Stille. Aceste architecturi sunt compuse dintr-un schelet terpiridinic (terpy) alc,tuind trupul fluturelui, la care au fost implementate dou, aripi porfirinice care sunt capabile sa varieze între o conforma,ie extins, în forma de liter, W ,i o conformai,ie compact, în form, de litera U, datorit, complexarii trupului terpy printr-un cation de talie ,i coordina,ie adecvat,. Aripile porfirinice se prezintã fie ca base libere sau, datorita unei metalari succesive cu diferite metale, pot avea diferite "culori". Studii de fluorescen,a atât sta,ionar, cât ,i rezolvat, în timp, asupra arhitecturilor HZn, ZnAu ,i Zn2Au, arat, c, proprit,,ile electronice sunt foarte dependente de geometria adoptat,. In conforma,ia W extins,, am putut pune în eviden,, un proces de transfer de energie dinspre baza liber, c,tre porfirina metalat, cu Zn. In conforma,ia U a Zn2Au luminescen,a aripei donoare, datorate st,rii singulet excitate, este puternic stins, nu numai datorit, efectului de atom greu, cât ,i a unui proces de transfer de electron c,tre starea fundamental, a aripei metalat, cu aur. Pe deasupra, complexând (,,,)-diamine c,tre atomii de ZnIIîntre tetrapirolii porfirinici, sunt induse profunde influen,e asupra conforma,iei sistemului. Pentru compusul Zn2Zn, care a putut fi crescut monocristalin, experimente de difrac,ie folosind ca surs, luminoas, un sincrotron au condus la un set de date care a permis ca structura sa fie elucidat, prin metode directe ,i rafinat,, ar,tând conforma,ia în U a,teptat,. Atomul central de Zn are o coordina,ie de sase unde pe lang, lignadul ,3 -terpy, atomul de Zn este coordinat de c,tre doi anioni acetat, unul monodentat, iar cel,lalt semi-chelatizant. Structura este br,zdat, de leg,turi de hidrogen care implic, liganzii apo,i situa,i pe centrii de Zn exteriori, ,i atomii de oxigen din ionii acetat. Sistemul prezentat este un dutblu efector, ar,tând comutare opto-mecanic,, datorat, fie lig,rii prin ioni metalici, fie prin al,i liganzi perfect croitori,i. In acel,i timp, atât procese de transfer de energie, cât ,i de electroni, pot fi perfect comutate, l,sând loc pentru imbun,t,,irea raportului "on/off" în arhitecturi viitoare. [source] Photophysical Processes in ,Supramolecular Balls' Formed by Lanthanide Chloride with 2,2,-BipyridineHELVETICA CHIMICA ACTA, Issue 11 2009Abstract The europium complex [EuCl2(bpy)2(H2O)2]Cl,1.25,C2H6O,0.37,H2O, where bpy is 2,2,-bipyridine, was synthesized and investigated with the aim to relate its molecular geometry and crystal packing to the efficiency of energy-transfer processes. The presence of H-bonds between noncoordinated Cl, ions and coordinated H2O molecules leads to the formation of discrete trimers assembled by a number of CH,,,Cl and stacking interactions into ,supramolecular balls' which contain Cl, ions and solvate molecules (H2O and EtOH). The additional stabilization of the complex is due to intramolecular N,,,C interactions between two bpy ligands that causes some shortening of the EuN bonds. Deciphering the luminescence properties of the Eu complex was performed under consideration of both the composition of the inner coordination sphere and the peculiarities of the crystal packing. The influence of the latter and the bpy orientation on the energy of the ligand,Eu charge-transfer state (LMCT) was established, and an additional excited state induced by the , -stacking interaction (SICT) was identified. [source] Dendrimeric Oligo(phenylenevinylene)-Extended Dithieno[3,2- b:2,,3,- d]phospholes,Synthesis, Self-Organization, and Optical PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2009Carlos Romero-Nieto Abstract A boost from the branches: Incorporation of the dithieno[3,2- b:2,,3,- d]phosphole system as a core in oligo(phenylenevinylene) dendrimers (an example is shown here) provides materials that exhibit energy-transfer features relaying incoming photons from the dendrons towards the core, which in turn shows enhanced emission intensity. The optical properties and self-assembly features of the dendrimers can be impacted by the terminal groups (-H, -CF3, or -NPh2) employed. To establish this system as a fluorescent core in ,-conjugated dendrimers, a series of oligo(phenylenevinylene) (OPV)-extended dithieno[3,2- b:2,,3,- d]phospholes has been prepared by means of a Wittig,Horner protocol with a dithienophosphole dialdehyde and appropriately functionalized phosphonates. The "zero-generation" model compounds have provided the general accessibility of OPV-functionalized dithienophospholes, and show varying emission colors covering the optical spectrum from green to red. Expansion of the synthetic strategy towards the corresponding first-generation dendrimers has provided materials that show intriguing self-organization features in case of the phenyl-terminated dendrimer, forming large one-dimensional microfibres, as well as desirable energy-transfer processes from the dendrons to the dithienophoshole core resulting in an enhanced emission intensity for the latter. The present study has revealed that the terminal end-groups of the OPV branches have significant impact on the optical features of the OPV dendrimers as a whole. [source] 2-Phenanthrenyl,DNA: Synthesis, Pairing, and Fluorescence PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2009Nikolay Abstract Three 2,-phenanthrenyl- C -deoxyribonucleosides with donor (phenNH2), acceptor (phenNO2), or no (phenH) substitution on the phenanthrenyl core were synthesized and incorporated into oligodeoxyribonucleotides. Duplexes containing either one or three consecutive phenR residues, which were located opposite each other, were formed. Within these residues, the phenR residues are expected to recognize each other through interstrand stacking interactions, in much the same way as described previously for biphenyl DNA. The thermal, thermodynamic, and fluorescence properties of such duplexes were determined by UV melting analysis and fluorescence spectroscopy. Depending on the nature of the substituent, the thermal stability of single-modified duplexes can vary between ,2.7 to +11.3,°C in Tm and that of triple-modified duplexes from +7.8 to +11.1,°C. Van,t Hoff analysis suggested that the observed higher thermodynamic stability in phenH- and phenNO2 -containing duplexes is of enthalpic origin. A single phenH or phenNO2 residue in a bulge position also stabilizes a corresponding duplex. If a phenNO2 residue is placed in a bulge position next to a base mismatch this can lead, in a sequence-dependent manner, to duplex destabilization. The phenNO2 residue was found to be a highly efficient (10,100-fold) quencher of phenH and phenNH2 fluorescence if placed in the opposite position to the fluorophores. When phenH and phenNH2 residues were placed opposite each other, efficient quenching of phenH and enhancement of phenNH2 fluorescence was found, which is an indicator for electron- or energy-transfer processes between the aromatic units. [source] Enhancement of Förster Energy Transfer within a Microspherical CavityCHEMPHYSCHEM, Issue 11 2005Hideki Fujiwara Dr. Abstract Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that Förster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra. [source] | ||||||||||