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On the existence of superradiant excitonic states in microtubules
摘要： Microtubules are biological protein polymers with critical and diverse functions. Their structures share some similarities with photosynthetic antenna complexes, particularly in the ordered arrangement of photoactive molecules with large transition dipole moments. As the role of photoexcitations in microtubules remains an open question, here we analyze tryptophan molecules, the amino acid building block of microtubules with the largest transition dipole strength. By taking their positions and dipole orientations from realistic models capable of reproducing tubulin experimental spectra, and using a Hamiltonian widely employed in quantum optics to describe light-matter interactions, we show that such molecules arranged in their native microtubule configuration exhibit a superradiant lowest exciton state, which represents an excitation fully extended on the chromophore lattice. We also show that such a superradiant state emerges due to supertransfer coupling between the lowest exciton states of smaller blocks of the microtubule. In the dynamics we find that the spreading of excitation is ballistic in the absence of external sources of disorder and strongly dependent on initial conditions. The velocity of photoexcitation spreading is shown to be enhanced by the supertransfer effect with respect to the velocity one would expect from the strength of the nearest-neighbor coupling between tryptophan molecules in the microtubule. Finally, such structures are shown to have an enhanced robustness to static disorder when compared to geometries that include only short-range interactions. These cooperative effects (superradiance and supertransfer) may induce ultra-efficient photoexcitation absorption and could enhance excitonic energy transfer in microtubules over long distances under physiological conditions.
关键词： quantum transport in disordered systems,energy transfer,open quantum systems,quantum biology
更新于2025-09-04 15:30:14
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Facile synthesis, morphology and tunable photoluminescence properties of BaMgF <sub/>4</sub> :Ce <sup>3+</sup> /Tb <sup>3+</sup> /Eu <sup>3+</sup> phosphors
摘要： A series of BaMgF4:Ce3+/Tb3+/Eu3+ phosphors were successfully prepared via a facile hydrothermal process. X-ray diffraction (XRD), energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), n-UV–UV-vis photoluminescence (PL) and fluorescence decays were employed to investigate the structure, composition, morphology, luminescence properties and energy transfer processes. The as-prepared BaMgF4 phosphors exhibit a rod-like morphology and the size of the product can be effectively regulated by changing the amount of NH4F in the original solution. Under n-UV–UV light excitation, the Ce3+, Tb3+ and Eu3+ singly-doped BaMgF4 phosphors all show good characteristic luminescence; the Ce3+–Tb3+ and Tb3+–Eu3+ co-doped BaMgF4 phosphors both show tunable emission colors from blue (green) to green (orange-red) because of the energy transfer of Ce3+ → Tb3+ and Tb3+ → Eu3+, respectively. Moreover, the efficient energy transfer from Ce3+ (Tb3+) to Tb3+ (Eu3+) ions in the co-doped samples was confirmed by investigating the excitation/emission spectra and decay lifetimes. The results indicate that the phosphors may be potentially used as single-component multi-color phosphors for white light-emitting diodes.
关键词： energy transfer,BaMgF4,white light-emitting diodes,phosphors,hydrothermal process
更新于2025-09-04 15:30:14
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Multichromophoric sugar for fluorescence photoswitching
摘要： A multichromophoric glucopyranoside 2 bearing three dicyanomethylenepyran (DCM) fluorophores and one diarylethene (DAE) photochrome has been prepared by Cu(I)-catalyzed alkyne–azide cycloaddition reaction. The fluorescence of 2 was switched off upon UV irradiation, in proportion with the open to closed form (OF to CF) conversion extent of the DAE moiety. A nearly 100% F?rster-type resonance energy transfer (FRET) from all three DCM moieties to a single DAE (in its CF) moiety was achieved. Upon visible irradiation, the initial fluorescence intensity was recovered. The observed photoswiching is reversible, with excellent photo resistance.
关键词： energy transfer,monosaccharide,photochromism,click chemistry,fluorophore
更新于2025-09-04 15:30:14
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Synthesis, Structural, Electrochemical and Energy Transfer Studies of π‐Extended Mono‐β‐Functionalized Porphyrin Dyads
摘要： A series of π-conjugated mono-β-functionalized donor-acceptor porphyrin dyads (1-4) with various (phenyl, naphthyl, anthracenyl and pyrenyl) donors and their metal complexes (M = Zn(1a-4a), Cu(1b-4b), Co(1c-4c) and Ni(1d-4d)) were synthesized and characterized by various spectroscopic and electrochemical techniques. Modified one-step Horner-Wadsworth-Emmons reaction was performed on monoformyl porphyrin to get ethenyl linked mono-β-porphyrin dyads in good to excellent yields (70-90%). Red shifted absorption and emission spectra were observed as compared to unsubstituted pristine tetraphenylporphyrins due to π-extended donors. Time resolved fluorescence studies confirmed the effective intramolecular F?rster energy transfer from donor moiety to porphyrin core in anthracene and pyrene appended porphyrin dyads. DFT and TD-DFT optimization signified the orientation of donor and acceptor plays a vital role in energy transfer as co-planarity of donor with porphyrin core increases the energy transfer efficiency. The distribution of electron density on HOMOs and LUMOs indicated the EET mechanism from donor moiety to porphyrin acceptor core. All porphyrin dyads exhibited cathodic shift in their oxidation potential suggesting facile oxidation of porphyrin core due to π-extension and the presence of electron donating moieties. Finally, femtosecond transient absorption spectral studies were performed to secure evidence of excitation transfer and kinetic information of the energy transfer event in the dyads.
关键词： DFT,energy transfer,mono-β-functionalized,porphyrin dyads,Horner-Wadsworth-Emmons reaction,π-Extended,femtosecond transient absorption,TD-DFT
更新于2025-09-04 15:30:14
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Electronic Couplings in (Bio-) Chemical Processes
摘要： During the last two decades, 2D optical techniques have been extended to the visible range, targeting electronic transitions. Since the report of the very first 2D electronic measurement (Hybl et al. in J Chem Phys 115:6606–6622, [2001]), two-dimensional electronic spectroscopy (2DES) has allowed fundamentally new insights into the structure and dynamics of condensed-phase systems (Ginsberg et al. in Acc Chem Res 42:1352–1363, 2009; Jonas in Annu Rev Phys Chem 54:425–463, 2003), producing experiments that measure correlations among electronic states of an absorbing species within complex systems. 2DES is used to investigate photophysical phenomena involving electronic or vibrational couplings in multi-chromophoric systems [energy transfer in photosynthesis is one great example of how 2DES can disentangle various energy transfer pathways (Brixner et al. in Nature 625–628, 2005; Engel et al. in Nature 446:782–786, 2007; Collini et al. in Nature 463:644–647, 2010)], but also ultrafast photochemical processes in which the tracked molecules change permanently or are heterogeneous (Ruetzel et al. in Proc Natl Acad Sci 111:4764–4769, 2014; Consani et al. in Science 339:1586–1589, 2013). We divide this chapter according to some of the major areas that have been established thanks to 2DES in the following fields: heterogeneity of systems, excitation energy transfer mechanisms, photo-induced coherent oscillations associated with electronic and vibrational couplings, and complex chemical reactions (Fig. 1).
关键词： Energy transfer,Vibronic coupling,Two-dimensional electronic spectroscopy,Photoreactivity,Heterogeneity
更新于2025-09-04 15:30:14
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Synthesis, energy transfer, charge compensation and luminescence properties of CaZrO3:Eu3+, Bi3+, Li+ phosphor
摘要： A series of CaZrO3:Bi3+, CaZrO3:Eu3+, CaZrO3:Eu3+, Bi3+, and CaZrO3:Eu3+, Bi3+, Li+ phosphors are synthesized by high-temperature solid-state reaction method in air. Their luminescence properties are researched, compared, and analyzed. CaZrO3:Bi3+ phosphor under excitation at 310?nm emits deep-blue light with chromaticity coordinate (0.1612, 0.0254). CaZrO3:Eu3+ phosphor under excitation at 310 and 395?nm shows red-emitting with chromaticity coordinate (0.6386, 0.3611). CaZrO3:Eu3+, Bi3+ phosphor under excitation at 310?nm exhibits a systematically varied hue from deep-blue to red light by changing Eu3+ ion concentration, and that with excitation at 395?nm only emits red light with chromaticity coordinate (0.6386, 0.3611). The energy transfer process from Bi3+ to Eu3+ ions may be indicated by their spectral properties. The optimal Eu3+ and Bi3+ ions concentrations are 5?mol% and 0.9?mol%, respectively. The emission intensity CaZrO3:Eu3+, Bi3+ phosphor may be enhanced about 1.6 times due to the co-doping Li+ ion as charge compensator role. The luminous mechanism of CaZrO3:Eu3+, Bi3+ phosphor is explained by the simplified energy level diagrams of Bi3+ and Eu3+ ions.
关键词： energy transfer,CaZrO3,luminescence,charge compensation,phosphor
更新于2025-09-04 15:30:14
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Facile Synthesis and Controllable Emission of Tm <sup>3+</sup> /Er <sup>3+</sup> -Doped and -Co-doped α-NaYbF <sub/>4</sub> Upconversion Nanocrystals
摘要： Tm3+, Er3+-doped and -co-doped α-NaYbF4 nanoparticles were synthesized via a facile hydrothermal route with oleic acid as the capping agent. Experimental results showed that the doped NaYbF4 nanoparticles possessed a cubic phase with the average size of ～13 nm. Upon excitation by a 980 nm laser, the as-synthesized nanoparticles exhibited blue and red upconversion emissions corresponding to the monodoped Tm3+, Er3+ in the cubic-phase NaYbF4, respectively, and intense green and red emissions in the Tm3+/Er3+-co-doped NaYbF4 nanoparticles. Furthermore, the possible energy transfer mechanism among Yb3+/Tm3+/Er3+ in α-NaYbF4 nanoparticles was also proposed. The cell toxicity test revealed that the as-synthesized upconversion nanoparticles possessed remarkably low cytotoxicity. All of the advantageous features including facile synthesis, controllable emission, and low cytotoxicity make the upconversion nanoparticles promising for multicolor bioimaging and anti-counterfeiting applications.
关键词： anti-counterfeiting applications,multicolor bioimaging,upconversion nanocrystals,hydrothermal synthesis,energy transfer mechanism,α-NaYbF4,low cytotoxicity,Tm3+/Er3+-doped
更新于2025-09-04 15:30:14
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Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State
摘要： The development of rigid covalent chiroptical organic materials, with multiple, readily available redox states, which exhibit high photoluminescence is of particular importance in relation to both organic electronics and photonics. The chemically stable, thermally robust and redox-active perylene diimide (PDI) fluorophores have received ever-increasing attention owing to their excellent fluorescence quantum yields in solution. Planar PDI derivatives, however, generally suffer from aggregation-caused emission quenching in the solid state. Herein, we report on the design and synthesis of two chiral isosceles triangles wherein one PDI fluorophore and two pyromellitic diimide (PMDI) or naphthalene diimide (NDI) units are arranged in a rigid cyclic triangular geometry. The optical, electronic and magnetic properties of the rigid isosceles triangles are fully characterized by a combination of optical spectroscopies, X-ray diffraction, cyclic voltammetry, and computational modeling techniques. Single-crystal X-ray diffraction analysis shows that both isosceles triangles form discrete, nearly cofacial PDI-PDI π-dimers in the solid state. While the triangles exhibit fluorescence quantum yields of almost unity in solution, the dimers in the solid state exhibit very weak — yet at least an order of magnitude higher — excimer fluorescence yield in comparison with the almost completely quenched fluorescence of a reference PDI. The triangle containing both NDI and PDI subunits shows superior intramolecular energy transfer from the lowest excited singlet state of the NDI to that of the PDI subunit. Cyclic voltammetry suggests that both isosceles triangles exhibit multiple, easily accessible and reversible redox states. Applications beckon in arenas related to molecular optoelectronic devices.
关键词： intramolecular energy transfer,isosceles triangles,rigid covalent chiroptical organic materials,naphthalene diimide,excimer fluorescence,redox-active,π-dimers,photoluminescence,perylene diimide,pyromellitic diimide,cyclic voltammetry
更新于2025-09-04 15:30:14
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Catalytic deracemization of chiral allenes by sensitized excitation with visible light
摘要： Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed. Frequently, however, only a single enantiomeric form of a chiral compound is required, which raises the question of how a racemate can be selectively converted into a single enantiomer. Such a deracemization process is entropically disfavoured and cannot be performed by a conventional catalyst in solution. Here we show that it is possible to photochemically deracemize chiral compounds with high enantioselectivity using irradiation with visible light (wavelength of 420 nanometres) in the presence of catalytic quantities (2.5 mole per cent) of a chiral sensitizer. We converted an array of 17 chiral racemic allenes into the respective single enantiomers with 89 to 97 per cent enantiomeric excess. The sensitizer is postulated to operate by triplet energy transfer to the allene, with different energy-transfer efficiencies for the two enantiomers. It thus serves as a unidirectional catalyst that converts one enantiomer but not the other, and the decrease in entropy is compensated by light energy. Photochemical deracemization enables the direct formation of enantiopure materials from a racemic mixture of the same compound, providing a novel approach to the challenge of creating asymmetry.
关键词： chiral sensitizer,triplet energy transfer,deracemization,chiral compounds,visible light,enantiomers,photochemical
更新于2025-09-04 15:30:14
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Responsive Upconversion Nanoprobe for Background‐Free Hypochlorous Acid Detection and Bioimaging
摘要： Responsive nanoprobes play an important role in bioassay and bioimaging, early diagnosis of diseases and treatment monitoring. Herein, a upconversional nanoparticle (UCNP)-based nanoprobe, Ru@UCNPs, for specific sensing and imaging of hypochlorous acid (HOCl) is reported. This Ru@UCNP nanoprobe consists of two functional components, i.e., NaYF4:Yb, Tm UCNPs that can convert near infrared light-to-visible light as the energy donor, and a HOCl-responsive ruthenium(II) complex [Ru(bpy)2(DNCH-bpy)](PF6)2 (Ru-DNPH) as the energy acceptor and also the upconversion luminescence (UCL) quencher. Within this luminescence resonance energy transfer nanoprobe system, the UCL OFF–ON emission is triggered specifically by HOCl. This triggering reaction enables the detection of HOCl in aqueous solution and biological systems. As an example of applications, the Ru@UCNPs nanoprobe is loaded onto test papers for semiquantitative HOCl detection without any interference from the background fluorescence. The application of Ru@UCNPs for background-free detection and visualization of HOCl in cells and mice is successfully demonstrated. This research has thus shown that Ru@UCNPs is a selective HOCl-responsive nanoprobe, providing a new way to detect HOCl and a new strategy to develop novel nanoprobes for in situ detection of various biomarkers in cells and early diagnosis of animal diseases.
关键词： imaging,nanoprobes,paper-based test strips,bioassay and bioimaging,luminescence resonance energy transfer,selective HOCl detection and imaging
更新于2025-09-04 15:30:14