The sensitive detection of X-rays embodies an important area of research, being motivated by a co... more The sensitive detection of X-rays embodies an important area of research, being motivated by a common desire to minimize the doses of ionising radiation required for detection. Amongst metal halide perovskites, the double perovskite Cs 2 AgBiBr 6 system has recently emerged as a highly promising candidate for the detection of X-rays, capable of high X-ray stability and sensitivity (105 µC.Gy −1 cm −2). Herein, we detail the important photophysical pathways in single crystal Cs 2 AgBiBr 6 at both room and liquid nitrogen temperatures, with emphasis made toward understanding the carrier dynamics which influence X-ray sensitivity. Our study draws upon a combination of optical probes and we develop a room temperature excitation model which is far from optimal, being plagued by a large trap density and fast recombination pathways above the conduction band minimum. We find that substantially improved operating conditions result at 77 K, due to a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. We characterise the temperature dependence of a single crystal Cs 2 AgBiBr 6 X-ray detecting device and reveal a strong and monotonic enhancement to the X-ray sensitivity upon cooling, moving from 316 µC.Gy −1 cm −2 at room temperature to 988 µC.Gy −1 cm −2 near liquid nitrogen temperatures. We conclude that even modest cooling-via thermoelectric Peltier device-will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.
The development of single-molecule imaging and super-resolution microscopic tequniques has promot... more The development of single-molecule imaging and super-resolution microscopic tequniques has promoted the study of fluorescence switchable molecules that have been important for the in-depth understanding of activities of organelles and geometries of materials in nano-and microscales. The utilization of photochromic compounds as the photo-switching trigger is one of the efficient strategies to reversibly control the fluorescent "ON" and "OFF" states. In this study, we demonstrated the red-color fluorescence switching of a perylene bisimide (PBI) derivative by using the fast photochromic [2.2]paracyclophanebridged imidazole dimer. The transient colored biradical species as the fluorescence quencher is generated upon UV light irradiation. Because the biradical species has broad absorption bands in the whole visible light and the near-infrared regions (500-900 nm), the fluorescence of PBI could be efficiently quenched by Förster resonance energy transfer (FRET). The fluorescence intensity was switched by the fast photochromic cycles within a few tens of milliseconds. The potential capability of the transient biradical species to switch the fluorescence in the visible and NIR regions will open up the multicolor fluorescence imaging.
The fluorescence intermittency or "blinking" of single molecules of ATTO647N (ATTO) in the conduc... more The fluorescence intermittency or "blinking" of single molecules of ATTO647N (ATTO) in the conductive matrix polyvinylcarbazole (PVK) is described in the presence of an external applied electric field. It is shown that due to the energy distribution of the highest occupied molecular orbital (HOMO) level of PVK, which is energetically close to the HOMO of ATTO, sporadic electron transfer occurs. As a result, the on/off dynamics of blinking can be influenced by the electric field. This field will, depending on the respective position and orientation of the dye/polymer system with respect to those of the electrodes, either enhance or suppress electron transfer from PVK to ATTO as well as the back electron transfer from reduced ATTO to PVK. After the charge-transfer step, the applied field will pull the hole in PVK away from the dye, increasing the overall time the dye resides in a dark state.
Photochemical and Photobiological Sciences, Dec 1, 2008
A detailed investigation of the photophysical properties of a series of perylenediimide systems b... more A detailed investigation of the photophysical properties of a series of perylenediimide systems bearing three different types of bay substituents is presented. Single photon timing and femtosecond transient absorption experiments reveal that the dynamics of interconversion between two conformational arrangements of these substituents occurs with a time constant of 550 ps. In addition, charge transfer from the electron-rich units attached to the bay area of the electron-poor perylenediimide core is observed. This process leads to a fast non-radiative deactivation of the locally excited state of the perylenediimide in polar solvents. When the experimental results of the investigated systems are compared we observe a shift from a conformational dynamics towards competitive excited state processes involving charge transfer in the-meta and-para substituted perylenediimide chromophore.
Metal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of ... more Metal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of guest molecules. Furthermore, the emissions of fluorescent molecules can be tuned by confinement. In this study, a solvent‐free “bottle‐around‐ship” method is used to encapsulate perylene and 9,10‐dimethylanthracene, two polycyclic aromatic hydrocarbons, in the MOF ZIF‐8. Luminescence color tuning is achieved, including white‐light emission, when controlling the loading of only a single type of guest. Photophysical analysis suggests that the variations in luminescence result from various guest arrangements in the nanocompartments, as well as host–guest interactions. Because of the tight confinement of the guests, this host–guest system displays excellent luminescence thermal stability.
The excited state properties of a peryleneimide-pentaphenylene dyad were investigated in detail u... more The excited state properties of a peryleneimide-pentaphenylene dyad were investigated in detail using pump-probe, single photon timing and three-beam pulsed experiments. Upon excitation with 395 nm pulses ultrafast energy transfer was found to occur from the pentaphenylene to the perylene subunit. In polar solvents this excitation energy transfer is followed by charge transfer from the electron donor pentaphenylene to the electron acceptor perylene. A three-beam femtosecond transient absorption technique revealed the relaxation dynamics of a higher lying singlet state of the peryleneimide subunit to occur on a picoseconds time scale. These results demonstrate the potential use of the three-beam femtosecond technique in manipulating excited states processes.
Carbonaceous particle exposure and air pollution in general lead to a multitude of adverse human ... more Carbonaceous particle exposure and air pollution in general lead to a multitude of adverse human health effects and pose multiple challenges in terms of exposure, risk and safety assessment. Highly desirable for fast screening are label-free approaches for detecting these particle types in biological or medical context. We report a powerful approach for detecting carbonaceous particles using photothermal pump-probe microscopy, which directly probes their strong light absorption. The principle and reliability of this approach is demonstrated by examining four different carbon black (CB) species modelling soot with diameters ranging from 13 to 500 nm. Our results show that the proposed approach is applicable to a large number of CB types as well as black carbon (BC). As the particles show a strong absorption over a wide spectral range as compared to other absorbing species, we can image CB particles almost background free. Our pump-probe approach allows label-free optical detection and unambiguous localization of CB particles in (bio)fluids and 3D cellular environments. In combination with fluorescence microscopy, this method allows for simultaneous colocalization of CB with different cellular components using fluorophores as shown here for human lung fibroblasts. We further demonstrate the versatility of pump-probe detection in a flow cell.
The epidermal growth factor (EGF) receptor transduces the extracellular EGF signal into the cells... more The epidermal growth factor (EGF) receptor transduces the extracellular EGF signal into the cells. The distribution of these EGF receptors in the plasma membrane is heterogeneous and dynamic, which is proposed to be important for the regulation of cell signaling. The response of the cells to a physiological concentration of EGF is not homogeneous, which makes it difficult to analyze the dynamics related to the response. Here we developed a system to perform functional imaging during single particle tracking (SPT) analysis. This system made it possible to observe the cytosolic Ca 2+ concentration to monitor the cell response while tracking individual EGF molecules and found that about half of the cells responded to the stimulation with 1.6 nM EGF. In the responding cells, the EGF receptor showed 3 modes of movement: fast (the diffusion coefficient of 0.081 ± 0.009 μm2/sec, 29 ± 9%), slow (0.020 ± 0.005 μm2/sec, 22 ± 6%), and stationary (49 ± 13%). The diffusion coefficient of the fast mode movement in the responding cells was significantly larger than that in the nonresponding cells (0.069 ± 0.009 μm2/sec, p < 0.05). The diffusion coefficient of the fast mode movement is thought to reflect the monomer–dimer equilibrium of the EGF receptor. We assumed that the feedback regulation via the Ca 2+ signaling pathway slightly shifts the equilibrium from dimer to monomer in the responding cells. [Formula: see text]Special Issue Comment: This research paper is about the diffusion of EGF receptors in the membrane. It is therefore related with various projects in this Special Issue: the reviews about FRET41 and enzymes,42 and the projects about solving single molecules trajectories.43
Defects influence the properties of metal-organic frameworks (MOFs) e.g. storage amount and diffu... more Defects influence the properties of metal-organic frameworks (MOFs) e.g. storage amount and diffusion kinetics of gas molecules. However, the spatial distribution of defects is still poorly understood due to a lack of visualization methods. Here, we present a new method using nonlinear optics (NLO) allowing visualization of defects within MOFs.
A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mgcontaining aluminophosphates with diff... more A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mgcontaining aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å x 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance. The study and simulation of different natural systems and processes has always attracted a great interest to scientists. In this regard, an interesting challenge is the design of artificial antenna systems by mimicking the photosynthesis process, in which
The first systematic steady-state and time-resolved emission study of firefly oxyluciferin (emitt... more The first systematic steady-state and time-resolved emission study of firefly oxyluciferin (emitter in firefly bioluminescence) and its analogues in aqueous buffers provided the individual emission spectra of all chemical forms of the emitter and the excited-state equilibrium constants in strongly polar environment with strong hydrogen bonding potential. The results confirmed the earlier hypothesis that excited-state proton transfer from the enol group is favored over proton transfer from the phenol group. In water, the phenol-keto form is the strongest photoacid among the isomers and its conjugate base (phenolate-keto) has the lowest emission energy (634 nm). Furthermore, for the first time we observed green emission (525 nm) from a neutral phenol-keto isomer constrained to the keto form by cyclopropyl substitution. The order of emission energies indicates that in aqueous solution a second deprotonation at the phenol group after the enol group had dissociated (that is, deprotonation of the phenol-enolate) does not occur in the first excited state. The pH-dependent emission spectra and the time-resolved fluorescence parameters revealed that the keto-enol tautomerism reaction, which can occur in a nonpolar environment (toluene) in the presence of a base, is not favored in water.
This chapter critically reviews the studies related to structural and photophysical properties of... more This chapter critically reviews the studies related to structural and photophysical properties of metal clusters within zeolites matrices and summarizes the progress made in understanding the host-guest interactions. The goal is to provide useful insight into the nature of such interactions and experiments used in identifying the excited state dynamics and the reaction mechanisms leading to the emitting species. Especially interesting are the combined experimental and computational approaches used to elucidate the structures and electronic transition of clusters inside the cavity. Although a number of excellent research articles have been published in the last years they only cover rather specific areas like organic photochemistry, confinement, charge transfer, theoretical modeling or photostimulated luminescence.
In this review, the literature on the novel fluorophore BOPHY is covered. This doubly boron-cente... more In this review, the literature on the novel fluorophore BOPHY is covered. This doubly boron-centered fluorophore resembles the well-studied BODIPY, but shows its own characteristics, both in synthesis and spectroscopy. We discuss the general synthesis and properties of this fluorophore, the possibilities for postmodifications, the literature on aromatic ring-fused BOPHY's and boron substitution.
The sensitive detection of X-rays embodies an important area of research, being motivated by a co... more The sensitive detection of X-rays embodies an important area of research, being motivated by a common desire to minimize the doses of ionising radiation required for detection. Amongst metal halide perovskites, the double perovskite Cs 2 AgBiBr 6 system has recently emerged as a highly promising candidate for the detection of X-rays, capable of high X-ray stability and sensitivity (105 µC.Gy −1 cm −2). Herein, we detail the important photophysical pathways in single crystal Cs 2 AgBiBr 6 at both room and liquid nitrogen temperatures, with emphasis made toward understanding the carrier dynamics which influence X-ray sensitivity. Our study draws upon a combination of optical probes and we develop a room temperature excitation model which is far from optimal, being plagued by a large trap density and fast recombination pathways above the conduction band minimum. We find that substantially improved operating conditions result at 77 K, due to a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. We characterise the temperature dependence of a single crystal Cs 2 AgBiBr 6 X-ray detecting device and reveal a strong and monotonic enhancement to the X-ray sensitivity upon cooling, moving from 316 µC.Gy −1 cm −2 at room temperature to 988 µC.Gy −1 cm −2 near liquid nitrogen temperatures. We conclude that even modest cooling-via thermoelectric Peltier device-will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.
The development of single-molecule imaging and super-resolution microscopic tequniques has promot... more The development of single-molecule imaging and super-resolution microscopic tequniques has promoted the study of fluorescence switchable molecules that have been important for the in-depth understanding of activities of organelles and geometries of materials in nano-and microscales. The utilization of photochromic compounds as the photo-switching trigger is one of the efficient strategies to reversibly control the fluorescent "ON" and "OFF" states. In this study, we demonstrated the red-color fluorescence switching of a perylene bisimide (PBI) derivative by using the fast photochromic [2.2]paracyclophanebridged imidazole dimer. The transient colored biradical species as the fluorescence quencher is generated upon UV light irradiation. Because the biradical species has broad absorption bands in the whole visible light and the near-infrared regions (500-900 nm), the fluorescence of PBI could be efficiently quenched by Förster resonance energy transfer (FRET). The fluorescence intensity was switched by the fast photochromic cycles within a few tens of milliseconds. The potential capability of the transient biradical species to switch the fluorescence in the visible and NIR regions will open up the multicolor fluorescence imaging.
The fluorescence intermittency or "blinking" of single molecules of ATTO647N (ATTO) in the conduc... more The fluorescence intermittency or "blinking" of single molecules of ATTO647N (ATTO) in the conductive matrix polyvinylcarbazole (PVK) is described in the presence of an external applied electric field. It is shown that due to the energy distribution of the highest occupied molecular orbital (HOMO) level of PVK, which is energetically close to the HOMO of ATTO, sporadic electron transfer occurs. As a result, the on/off dynamics of blinking can be influenced by the electric field. This field will, depending on the respective position and orientation of the dye/polymer system with respect to those of the electrodes, either enhance or suppress electron transfer from PVK to ATTO as well as the back electron transfer from reduced ATTO to PVK. After the charge-transfer step, the applied field will pull the hole in PVK away from the dye, increasing the overall time the dye resides in a dark state.
Photochemical and Photobiological Sciences, Dec 1, 2008
A detailed investigation of the photophysical properties of a series of perylenediimide systems b... more A detailed investigation of the photophysical properties of a series of perylenediimide systems bearing three different types of bay substituents is presented. Single photon timing and femtosecond transient absorption experiments reveal that the dynamics of interconversion between two conformational arrangements of these substituents occurs with a time constant of 550 ps. In addition, charge transfer from the electron-rich units attached to the bay area of the electron-poor perylenediimide core is observed. This process leads to a fast non-radiative deactivation of the locally excited state of the perylenediimide in polar solvents. When the experimental results of the investigated systems are compared we observe a shift from a conformational dynamics towards competitive excited state processes involving charge transfer in the-meta and-para substituted perylenediimide chromophore.
Metal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of ... more Metal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of guest molecules. Furthermore, the emissions of fluorescent molecules can be tuned by confinement. In this study, a solvent‐free “bottle‐around‐ship” method is used to encapsulate perylene and 9,10‐dimethylanthracene, two polycyclic aromatic hydrocarbons, in the MOF ZIF‐8. Luminescence color tuning is achieved, including white‐light emission, when controlling the loading of only a single type of guest. Photophysical analysis suggests that the variations in luminescence result from various guest arrangements in the nanocompartments, as well as host–guest interactions. Because of the tight confinement of the guests, this host–guest system displays excellent luminescence thermal stability.
The excited state properties of a peryleneimide-pentaphenylene dyad were investigated in detail u... more The excited state properties of a peryleneimide-pentaphenylene dyad were investigated in detail using pump-probe, single photon timing and three-beam pulsed experiments. Upon excitation with 395 nm pulses ultrafast energy transfer was found to occur from the pentaphenylene to the perylene subunit. In polar solvents this excitation energy transfer is followed by charge transfer from the electron donor pentaphenylene to the electron acceptor perylene. A three-beam femtosecond transient absorption technique revealed the relaxation dynamics of a higher lying singlet state of the peryleneimide subunit to occur on a picoseconds time scale. These results demonstrate the potential use of the three-beam femtosecond technique in manipulating excited states processes.
Carbonaceous particle exposure and air pollution in general lead to a multitude of adverse human ... more Carbonaceous particle exposure and air pollution in general lead to a multitude of adverse human health effects and pose multiple challenges in terms of exposure, risk and safety assessment. Highly desirable for fast screening are label-free approaches for detecting these particle types in biological or medical context. We report a powerful approach for detecting carbonaceous particles using photothermal pump-probe microscopy, which directly probes their strong light absorption. The principle and reliability of this approach is demonstrated by examining four different carbon black (CB) species modelling soot with diameters ranging from 13 to 500 nm. Our results show that the proposed approach is applicable to a large number of CB types as well as black carbon (BC). As the particles show a strong absorption over a wide spectral range as compared to other absorbing species, we can image CB particles almost background free. Our pump-probe approach allows label-free optical detection and unambiguous localization of CB particles in (bio)fluids and 3D cellular environments. In combination with fluorescence microscopy, this method allows for simultaneous colocalization of CB with different cellular components using fluorophores as shown here for human lung fibroblasts. We further demonstrate the versatility of pump-probe detection in a flow cell.
The epidermal growth factor (EGF) receptor transduces the extracellular EGF signal into the cells... more The epidermal growth factor (EGF) receptor transduces the extracellular EGF signal into the cells. The distribution of these EGF receptors in the plasma membrane is heterogeneous and dynamic, which is proposed to be important for the regulation of cell signaling. The response of the cells to a physiological concentration of EGF is not homogeneous, which makes it difficult to analyze the dynamics related to the response. Here we developed a system to perform functional imaging during single particle tracking (SPT) analysis. This system made it possible to observe the cytosolic Ca 2+ concentration to monitor the cell response while tracking individual EGF molecules and found that about half of the cells responded to the stimulation with 1.6 nM EGF. In the responding cells, the EGF receptor showed 3 modes of movement: fast (the diffusion coefficient of 0.081 ± 0.009 μm2/sec, 29 ± 9%), slow (0.020 ± 0.005 μm2/sec, 22 ± 6%), and stationary (49 ± 13%). The diffusion coefficient of the fast mode movement in the responding cells was significantly larger than that in the nonresponding cells (0.069 ± 0.009 μm2/sec, p < 0.05). The diffusion coefficient of the fast mode movement is thought to reflect the monomer–dimer equilibrium of the EGF receptor. We assumed that the feedback regulation via the Ca 2+ signaling pathway slightly shifts the equilibrium from dimer to monomer in the responding cells. [Formula: see text]Special Issue Comment: This research paper is about the diffusion of EGF receptors in the membrane. It is therefore related with various projects in this Special Issue: the reviews about FRET41 and enzymes,42 and the projects about solving single molecules trajectories.43
Defects influence the properties of metal-organic frameworks (MOFs) e.g. storage amount and diffu... more Defects influence the properties of metal-organic frameworks (MOFs) e.g. storage amount and diffusion kinetics of gas molecules. However, the spatial distribution of defects is still poorly understood due to a lack of visualization methods. Here, we present a new method using nonlinear optics (NLO) allowing visualization of defects within MOFs.
A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mgcontaining aluminophosphates with diff... more A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mgcontaining aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å x 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance. The study and simulation of different natural systems and processes has always attracted a great interest to scientists. In this regard, an interesting challenge is the design of artificial antenna systems by mimicking the photosynthesis process, in which
The first systematic steady-state and time-resolved emission study of firefly oxyluciferin (emitt... more The first systematic steady-state and time-resolved emission study of firefly oxyluciferin (emitter in firefly bioluminescence) and its analogues in aqueous buffers provided the individual emission spectra of all chemical forms of the emitter and the excited-state equilibrium constants in strongly polar environment with strong hydrogen bonding potential. The results confirmed the earlier hypothesis that excited-state proton transfer from the enol group is favored over proton transfer from the phenol group. In water, the phenol-keto form is the strongest photoacid among the isomers and its conjugate base (phenolate-keto) has the lowest emission energy (634 nm). Furthermore, for the first time we observed green emission (525 nm) from a neutral phenol-keto isomer constrained to the keto form by cyclopropyl substitution. The order of emission energies indicates that in aqueous solution a second deprotonation at the phenol group after the enol group had dissociated (that is, deprotonation of the phenol-enolate) does not occur in the first excited state. The pH-dependent emission spectra and the time-resolved fluorescence parameters revealed that the keto-enol tautomerism reaction, which can occur in a nonpolar environment (toluene) in the presence of a base, is not favored in water.
This chapter critically reviews the studies related to structural and photophysical properties of... more This chapter critically reviews the studies related to structural and photophysical properties of metal clusters within zeolites matrices and summarizes the progress made in understanding the host-guest interactions. The goal is to provide useful insight into the nature of such interactions and experiments used in identifying the excited state dynamics and the reaction mechanisms leading to the emitting species. Especially interesting are the combined experimental and computational approaches used to elucidate the structures and electronic transition of clusters inside the cavity. Although a number of excellent research articles have been published in the last years they only cover rather specific areas like organic photochemistry, confinement, charge transfer, theoretical modeling or photostimulated luminescence.
In this review, the literature on the novel fluorophore BOPHY is covered. This doubly boron-cente... more In this review, the literature on the novel fluorophore BOPHY is covered. This doubly boron-centered fluorophore resembles the well-studied BODIPY, but shows its own characteristics, both in synthesis and spectroscopy. We discuss the general synthesis and properties of this fluorophore, the possibilities for postmodifications, the literature on aromatic ring-fused BOPHY's and boron substitution.
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Papers by Eduard Fron