Harvesting luminescence via harnessing the photophysical properties of transition metal complexes

Chou, Pi‐Tai; Chi, Yun; Chung, Min‐Wen; Lin, Chao-Chen

doi:10.1016/j.ccr.2010.12.013

Cited by 304 publications

(176 citation statements)

References 80 publications

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“…Another possibility for the observed subpicosecond dynamics is intersystem crossing (ISC) that commonly takes place in transition-metal complexes. Although ISC has not been well studied in solid-state metal oxides, this nonadiabatic process can occur with anomalously fast rates (tens to hundreds of femtoseconds) in transition-metal complexes in solution following an initial metalto-ligand-charge-transfer photoexcitation, (25,57,58) Figure 7A. The amplitude of the initial maximum and the plateau at a time after 1 ps both scale with the pump power used; thus, the possibility of multiphoton excitation can be excluded.…”

Section: 1static Xuv Absorption Spectrum and Fitting Resultsmentioning

confidence: 99%

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

et al. 2014

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The identities of photoexcited states in thin-film Co 3 O 4 and the ultrafast carrier relaxation dynamics of Co 3 O 4 are investigated with oxidation-state-specific pump−probe femtosecond core level spectroscopy. A thin-film sample is excited near the 2.8 eV optical absorption peak, and the resulting spectral changes at the 58.9 eV M 2,3edge of cobalt are probed in transient absorption with femtosecond highorder harmonic pulses generated by a Ti/sapphire laser. The initial transient state shows a significant 2 eV redshift in the absorption edge compared to the static ground state, which indicates a reduction of the cobalt valence charge. This is confirmed by a charge transfer multiplet spectral simulation, which finds the experimentally observed extreme ultraviolet (XUV) spectrum matches the specific O 2− (2p) → Co 3+ (e g ) charge-transfer transition, out of six possible excitation pathways involving Co 3+ and Co 2+ in the mixed-valence material. The initial transient state has a power-dependent amplitude decay (190 ± 10 fs at 13.2 mJ/cm 2 ) together with a slight redshift in spectral shape (535 ± 33 fs), which are ascribed to hot carrier relaxation to the band edge. The faster amplitude decay is possibly due to a decrease of charge carrier density via an Auger mechanism, as the decay rate increases when more excitation fluence is used. This study takes advantage of the oxidation-state-specificity of time-resolved XUV spectroscopy, further establishing the method as a new approach to measure ultrafast charge carrier dynamics in condensed-phase systems.

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Section: 1static Xuv Absorption Spectrum and Fitting Resultsmentioning

confidence: 99%

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

et al. 2014

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“…A necessary -though not sufficient -condition for efficient SOC is the presence of an element with a high SOC constant ζ; since ζ increases with the fourth power of the atomic number, this equates to heavy elements in the periodic table. The pathways by which SOC operates are complicated, but a further condition is that the element plays a role in an excited state thermally accessible from the phosphorescent (normally T 1 ) state [18,19]. The past 15 years has witnessed intense activity in the design and synthesis of complexes of second-and third-row transition metal ions which satisfy these criteria, particularly those which feature significant metal-to-ligand charge-transfer (MLCT) character in their lowest excited states, leading -in some cases -to intense phosphorescence even in solution at room temperature.…”

Section: Phosphorescence Versus Fluorescence: Longer Lifetimesmentioning

confidence: 99%

Time-Resolved Emission Imaging Microscopy Using Phosphorescent Metal Complexes: Taking FLIM and PLIM to New Lengths

Baggaley

Weinstein

Williams

2014

Luminescent and Photoactive Transition Metal Complexes as Biomolecular Probes and Cellular Reagents

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Luminescent metal complexes are increasingly being investigated as emissive probes and sensors for cell imaging using what is traditionally termed fluorescence microscopy. The nature of the emission in the case of second-and third-row metal complexes is phosphorescence rather than fluorescence, as it emanates from triplet rather than singlet excited states, but the usual terminology overlooks the distinction between the quantum mechanical origins of the processes. In steady-state imaging, such metal complexes may be alternatives to widely used fluorescent organic molecules, used in exactly the same way but offering advantages such as ease of synthesis and colour tuning. However, there is a striking difference compared to fluorescent organic molecules, namely the much longer lifetime of phosphorescence compared to fluorescence. Phosphorescence lifetimes of metal complexes are typically around a microsecond compared to the nanosecond values found for fluorescence of organic molecules. In this contribution, we will discuss how these long lifetimes can be put to practical use. Applications such as time-gated imaging allow discrimination from background fluorescence in cells and tissues, while increased sensitivity to quenchers provides a means of designing more responsive probes, for example, for oxygen. We also describe how the technique of fluorescence lifetime imaging microscopy (FLIM) -which provides images based on lifetimes at different points in the image -can be extended from the usual nanosecond range to microseconds. Key developments in instrumentation as well as the properties of complexes suitable for the purpose are discussed, including the use of two-photon excitation methods. A number of different research groups have made pioneering contributions to the instrumental set-ups, but the E. Baggaley and J.A. Weinstein Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK e-mail: liz.baggaley@sheffield.ac.uk; julia.weinstein@sheffield.ac.uk J.A.G. Williams (*) Department of Chemistry, Durham University, Durham DH1 3LE, UK e-mail: j.a.g.williams@durham.ac.uk terminology and acronyms have not developed in a systematic way. We review the distinction between time-gating (to eliminate background emission) and true timeresolved imaging (whereby decay kinetics at each point in an image are monitored). For instance, terms such as PLIM (phosphorescence lifetime imaging microscopy) and TRLM (time-resolved luminescence microscopy) refer essentially to the same technique, whilst TREM (time-resolved emission imaging microscopy) embraces these long timescale methods as well as the more well-established technique of FLIM.Keywords Cell imaging Á Fluorescence Á Fluorescence lifetime imaging microscopy Á Imaging Á Iridium Á Metal complex Á Microscopy Á Oxygen sensing Á Phosphorescence Á Phosphorescence lifetime imaging microscopy Á Platinum Á Ruthenium Á Time-resolved emission imaging microscopy Á Time-resolved fluorescence Á Time-resolved luminescence microscopy Á Tissue imaging

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“…The lack of a photoresponse could result from a limited absorptivity for the excitation light, the quenching of emission by surface impurities/defects on the host, and/or an improper orientation towards the host surface. 32 However, based on energy-gap theory 33 and literature reports on CNTs 34 and complexes of ruthenium and other late transition metals, 35 we conclude that it more likely is due to nonradiation relaxation, because the CNT host can be regarded as an extension of the phenanthroline moiety. The increased distance between the electron donor and acceptor lowers the triplet state, but it also increases the probability of vibrational matching between the luminescent state and S 0 .…”

Section: Resultsmentioning

confidence: 93%

Photomagnetic Carbon Nanotubes at Ambient Conditions

et al. 2015

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KEYWORDSbis(2,2-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II), carbon nanotube, diazotization, photoinduced charge transfer, photomagnetism ABSTRACT Bis(2,2-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (Ru(bpy) 2 (phen-NH 2 ) 2+ ), an MLCT complex, has a long-lived triplet state in water (λ ex :473 nm; λ em : 620 nm; τ = 615 ns; Φ = 1 relative to that of Ru(bpy) 3 2+ ) and a structure analogous to Ru(bpy) 3 2+ . When Ru(bpy) 2 (phen-NH 2 ) 2+ was subjected to diazotization in the presence of carbon nanotubes (CNTs), it formed nanodots on the CNTs, rendering the resulting tubes (Ru@CNT) capable of transducing photo stimuli (473 nm) into electricity and magnetism at ambient conditions. The increased functionality was highly reproducible, as evidenced by conductive-mode AFM, vibrating sample magnetometry (VSM), and AC susceptibility analysis. The local magnetism probing of the Ru@CNT with magnetic-mode AFM techniques (MFM) indicated that the magnetism originated from the unpaired electrons formed on the photoexcited nanodots. The resulting phase shift behaved as a function of the luminous power and the voltage (V b ) of the electrical bias applied to the Ru@CNT. The V b dependence deviated from the expected quadratic correlation, confirming that the formation of the photoinduced charge separation state at the nanodots is responsible for the photomagnetism. The Ru@CNT tubes showed mobility toward external magnets (65 Gauss) when floating on water and under 473-nm illumination.The Ru@CNT thus appears to be a multifunctional material that might be useful in spintronics.

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Harvesting luminescence via harnessing the photophysical properties of transition metal complexes

Cited by 304 publications

References 80 publications

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

Time-Resolved Emission Imaging Microscopy Using Phosphorescent Metal Complexes: Taking FLIM and PLIM to New Lengths

Photomagnetic Carbon Nanotubes at Ambient Conditions

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Harvesting luminescence via harnessing the photophysical properties of transition metal complexes

Cited by 304 publications

References 80 publications

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co3O4)

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co3O4)

Time-Resolved Emission Imaging Microscopy Using Phosphorescent Metal Complexes: Taking FLIM and PLIM to New Lengths

Photomagnetic Carbon Nanotubes at Ambient Conditions

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Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)