Controlling electron exchange in molecular assemblies

Benniston, Andrew C.; Harriman, Anthony

doi:10.1016/j.ccr.2007.10.006

Cited by 37 publications

(20 citation statements)

References 87 publications

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“…5 The current contribution provides an unusual example of such behavior facilitating energy-transfer in d/f systems, and to the best of our knowledge, this is the first demonstration of d-f energy transfer by such a stepwise method. Given the current interest in dual-emissive d/f complexes for applications from display devices to cellular imaging as described above, 1−3 understanding the energy-transfer process which controls their luminescence behavior is of considerable importance.…”

Section: Introductionmentioning

confidence: 66%

d→f Energy Transfer in Ir(III)/Eu(III) Dyads: Use of a Naphthyl Spacer as a Spatial and Energetic “Stepping Stone”

et al. 2013

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A series of luminescent complexes based on {Ir(phpy)2} (phpy = cyclometallating anion of 2-phenylpyridine) or {Ir(F2phpy)2} [F2phpy = cyclometallating anion of 2-(2′,4′-difluorophenyl)pyridine] units, with an additional 3-(2-pyridyl)-pyrazole (pypz) ligand, have been prepared; fluorination of the phenylpyridine ligands results in a blue-shift of the usual 3MLCT/3LC luminescence of the Ir unit from 477 to 455 nm. These complexes have pendant from the coordinated pyrazolyl ring an additional chelating 3-(2-pyridyl)-pyrazole unit, separated via a flexible chain containing a naphthalene-1,4-diyl or naphthalene-1,5-diyl spacer. Crystal structures show that the flexibility of the pendant chain allows the naphthyl group to lie close to the Ir core and participate in a π-stacking interaction with a coordinated phpy or F2phpy ligand. Luminescence spectra show that, whereas the {Ir(phpy)2(pypz)} complexes show typical Ir-based emission—albeit with lengthened lifetimes because of interaction with the stacked naphthyl group—the {Ir(F2phpy)2(pypz)} complexes are nearly quenched. This is because the higher energy of the Ir-based 3MLCT/3LC excited state can now be quenched by the adjacent naphthyl group to form a long-lived naphthyl-centered triplet (3nap) state which is detectable by transient absorption. Coordination of an {Eu(hfac)3} unit (hfac = 1,1,1,5,5,5-hexafluoro-pentane-2,4-dionate) to the pendant pypz binding site affords Ir–naphthyl–Eu triads. For the triads containing a {Ir(phpy)2} core, the unavailability of the 3nap state (not populated by the Ir-based excited state which is too low in energy) means that direct Ir→Eu energy-transfer occurs in the same way as in other flexible Ir/Eu complexes. However for the triads based on the{Ir(F2phpy)2} core, the initial Ir→3nap energy-transfer step is followed by a second, slower, 3nap→Eu energy-transfer step: transient absorption measurements clearly show the 3nap state being sensitized by the Ir center (synchronous Ir-based decay and 3nap rise-time) and then transferring its energy to the Eu center (synchronous 3nap decay and Eu-based emission rise time). Thus the 3nap state, which is energetically intermediate in the {Ir(F2phpy)2}–naphthyl–Eu systems, can act as a “stepping stone” for two-step d→f energy-transfer.

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Section: Introductionmentioning

confidence: 66%

d→f Energy Transfer in Ir(III)/Eu(III) Dyads: Use of a Naphthyl Spacer as a Spatial and Energetic “Stepping Stone”

et al. 2013

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“…In the tpy–C 6 H 4 –NH 2 moiety π conjugation and planarization is more pronounced than in the tpy–C 6 H 4 –COOH unit as seen in the calculated pyridine–C 6 H 4 X torsion angles of α =–21°/–22° ( 1d , 1g ) and α = –33° ( 1e , 1g ) and the lengths of the corresponding interannular C–C bonds [1.446 Å ( 1d )/1.467 Å ( 1g ) and 1.485 Å ( 1e , 1g )]. As the degree of electronic coupling through π systems varies with the torsion angle between the π systems with cos 2 α 24 electron delocalization is reduced to ≈︁70 % within the tpy–C 6 H 4 –COOH systems and to ≈︁87 % within the tpy–C 6 H 4 –NH 2 units relative to the hypothetical planar systems. From a geometrical point of view, the electron accepting capability of tpy–C 6 H 4 –COOH is significantly reduced as compared to tpy–COOH, whereas the electron donating capability of tpy–C 6 H 4 –NH 2 relative to that of tpy‐NH 2 is still quite pronounced.…”

Section: Resultsmentioning

confidence: 99%

Cover Picture: Optimum Energy‐Dispersive X‐Ray Spectroscopy Elemental Mapping for Advanced Catalytic Materials (ChemCatChem 9/2013)

Zhang¹,

Zhang²,

Shao³

2013

ChemCatChem

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Cartography for the catalysis researcherThe cover picture shows that the observation of individual elements in advanced catalytic materials can be achieved by determining optimum conditions for obtaining an accurate STEM-EDX elemental map. In their Communication on p. 2586 ff., D. S. Su et al. reveal that a suitable combination of dwell time and beam intensity is crucial in pinpointing elemental distribution by using STEM-EDX mapping. Importantly, trace amounts of catalytic species can be observed towards the analytical limit to determine information, such as elemental composition, size, and morphology, as well as, in particular, the possible dynamic changes in nanoparticles after catalytic reactions.

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“…Formation of the Excited-State Equilibrium. It has been reported in recent work on terpyridineÀporphyrin architectures 43,44 and dinuclear metal complexes 24,26,25,45 that transitions between triplet-states require orbital overlap of the donor and the acceptor states, which is indicated for the complexes investigated here by TDDFT calculations. Thus, to study the dynamic formation of the excited-state equilibrium, which was discussed to significantly impact the luminescent properties of the complexes at hand, transient-absorption spectroscopy was performed.…”

Section: Theoretical Investigation Of the Lowest Triplet-statesmentioning

confidence: 94%

Direct Observation of Temperature-Dependent Excited-State Equilibrium in Dinuclear Ruthenium Terpyridine Complexes Bearing Electron-Poor Bridging Ligands

et al. 2011

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b S Supporting Information INTRODUCTIONThe formation of long-lived charge-separated states represents a key challenge in organic semiconductor research due to the positive effect of such states on the exciton diffusion length, 1 which presents a central metric for the performance of organic semiconductors. Several approaches dealing with this challenge are focused on the connection of coordination compounds to well-known conjugated polymeric structures. 2 One of the simplest ways to achieve long-lived charge-separated excited states is to create coordination polymers from conjugated linker segments and a suitable metal ion, e.g., from conjugated bisterpyridines and ruthenium(II) ions. 3 Conjugated bis-terpyridines represent the most suitable bridging ligand systems as they are readily synthesized and combine a great deal of structural variation of the chromophore with a high affinity to form ruthenium-based coordination polymers. 4À8 Furthermore, following this strategy the unfavorable photophysical properties of [Ru(terpy) 2 ] 2þ , i.e., a short room-temperature lifetime and a low emission quantum yield, 9 can be overcome. These properties, which limit the use of [Ru(terpy) 2 ] 2þ in, e.g., luminescent devices, are caused by efficient internal conversion between the lowest metal-to-ligand charge transfer ( 3 MLCT) excited-state

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Controlling electron exchange in molecular assemblies

Cited by 37 publications

References 87 publications

d→f Energy Transfer in Ir(III)/Eu(III) Dyads: Use of a Naphthyl Spacer as a Spatial and Energetic “Stepping Stone”

d→f Energy Transfer in Ir(III)/Eu(III) Dyads: Use of a Naphthyl Spacer as a Spatial and Energetic “Stepping Stone”

Cover Picture: Optimum Energy‐Dispersive X‐Ray Spectroscopy Elemental Mapping for Advanced Catalytic Materials (ChemCatChem 9/2013)

Direct Observation of Temperature-Dependent Excited-State Equilibrium in Dinuclear Ruthenium Terpyridine Complexes Bearing Electron-Poor Bridging Ligands

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