| 1. |
- Edhborg, Fredrik, 1990, et al.
(author)
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Singlet Energy Transfer in Anthracene-Porphyrin Complexes: Mechanism, Geometry, and Implications for Intramolecular Photon Upconversion
- 2019
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 123:46, s. 9934-9943
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Journal article (peer-reviewed)abstract
- In this work we show that the mechanism for singlet excitation energy transfer (SET) in coordination complexes changes upon changing a single atom. SET is governed by two different mechanisms; Förster resonance energy transfer (FRET) based on Coulombic, through-space interactions, or Dexter energy transfer relying on exchange, through-bond interactions. On the basis of time-resolved fluorescence and transient absorption measurements, we conduct a mechanistic study of SET from a set of photoexcited anthracene donors to axially coordinated porphyrin acceptors, revealing the effect of coordination geometry and a very profound effect of the porphyrin central metal atom. We found that FRET is the dominating mechanism of SET for complexes with zinc-octaethylporphyrin (ZnOEP) as the acceptor, while Dexter energy transfer is the dominating mechanism of SET in a corresponding ruthenium complex (RuOEP). In addition, by analyzing the coordination geometry of the complexes and its temperature dependence, the binding angle potential energy of axially coordinated porphyrin complexes could be estimated. The results of this study are of fundamental importance and are discussed with respect to the consequences for developing intramolecular triplet-Triplet annihilation photon upconversion in coordination complexes.
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| 2. |
- Gray, Victor, 1988, et al.
(author)
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Singlet and triplet energy transfer dynamics in self-assembled axial porphyrin-anthracene complexes: Towards supra-molecular structures for photon upconversion
- 2018
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 20:11, s. 7549-7558
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Journal article (peer-reviewed)abstract
- Energy and electron transfer reactions are central to many different processes and research fields, from photosynthesis and solar energy harvesting to biological and medical applications. Herein we report a comprehensive study of the singlet and triplet energy transfer dynamics in porphyrin-anthracene coordination complexes. Seven newly synthesized pyridine functionalized anthracene ligands, five with various bridge lengths and two dendrimer structures containing three and seven anthracene units, were prepared. We found that triplet energy transfer from ruthenium octaethylporphyrin to an axially coordinated anthracene is possible, and is in some cases followed by back triplet energy tra nsfer to the porphyrin. The triplet energy transfer follows an exponential distance dependence with an attenuation factor, β, of 0.64 Å -1 . Further, singlet energy transfer from anthracene to the ruthenium porphyrin appears to follow a R 6 Förster distance dependence. Porphyrin-anthracene complexes are also used as triplet sensitizers for triplet-triplet annihilation (TTA) based photon upconversion, demonstrating their potential for photophysical and photochemical applications. The triplet lifetime of the complex is extended by the anthracene ligands, resulting in a threefold increase in the upconversion efficiency, Φ UC to 4.5%, compared to the corresponding ruthenium porphyrin-pyridine complex. Based on the results herein we discuss the future design of supra-molecular structures for TTA upconversion.
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| 3. |
- Kücüköz, Betül, 1988, et al.
(author)
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Boosting Second-Harmonic Generation in Monolayer Rhenium Disulfide by Reversible Laser Patterning
- 2022
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In: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:2, s. 518-526
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Journal article (peer-reviewed)abstract
- Active modification and control of transition metal dichalcogenides (TMDs) properties are highly desirable for next-generation optoelectronic applications. In particular, controlling one of the most important characteristics of TMDs─their crystal structure and symmetry─may open means for manipulating their optical nonlinearities and electrical transport properties. Here, we show that a monolayer ReS2, which does not have a broken inversion symmetry due to its stable 1T′-distorted phase and correspondingly shows only weak second-harmonic generation (SHG), can produce a significantly enhanced (∼2 orders of magnitude) SHG upon reversible laser patterning. This enhancement can be explained by the laser-induced transition from centrosymmetric 1T′ to noncentrosymmetric 2H-phase. This hypothesis is confirmed by polarization-resolved SHG measurements, which reveal a gradual change from the 2-fold to 6-fold symmetry profiles upon laser patterning. Additionally, we found that laser patterning of the bilayer ReS2 samples, contrary to the monolayers, leads to a substantially reduced SHG signal. This result corroborates the 1T′-to-2H laser-induced phase transition. Finally, we show that the laser-induced patterning is reversible by heat. These results open a possibility to actively and reversibly control the crystal structure of mono- and few-layer ReS2 and thus its optical and electronic properties.
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| 4. |
- Munkhbat, Battulga, 1988, et al.
(author)
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Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics
- 2023
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In: Laser and Photonics Reviews. - : Wiley. - 1863-8899 .- 1863-8880. ; 17:1
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Journal article (peer-reviewed)abstract
- Transition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indices and optical anisotropy. Here, this vision is extended to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes with ultra sharp walls, as well as proof-of-concept all-TMD waveguides and resonators. Specific focus is given to various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods, especially for non-conductiven but relevant for nanophotonic applications substrates, such as SiO2. The specific materials studied here include semiconducting WS2, in-plane anisotropic ReS2, and metallic TaSe2, TaS2, and NbSe2. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high-index nanophotonics, plasmonics and on-chip optical circuits. The knowledge of TMD material-dependent nanofabrication parameters developed here will help broaden the scope of future applications of all-TMD nanophotonics.
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| 5. |
- Munkhbat, Battulga, 1988, et al.
(author)
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Tunable self-assembled Casimir microcavities and polaritons
- 2021
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 597:7875, s. 214-219
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Journal article (peer-reviewed)abstract
- Spontaneous formation of ordered structures—self-assembly—is ubiquitous in nature and observed on different length scales, ranging from atomic and molecular systems to micrometre-scale objects and living matter1. Self-ordering in molecular and biological systems typically involves short-range hydrophobic and van der Waals interactions2,3. Here we introduce an approach to micrometre-scale self-assembly based on the joint action of attractive Casimir and repulsive electrostatic forces arising between charged metallic nanoflakes in an aqueous solution. This system forms a self-assembled optical Fabry–Pérot microcavity with a fundamental mode in the visible range (long-range separation distance about 100–200 nanometres) and a tunable equilibrium configuration. Furthermore, by placing an excitonic material in the microcavity region, we are able to realize hybrid light–matter states (polaritons4–6), whose properties, such as coupling strength and eigenstate composition, can be controlled in real time by the concentration of ligand molecules in the solution and light pressure. These Casimir microcavities could find future use as sensitive and tunable platforms for a variety of applications, including opto-mechanics7, nanomachinery8 and cavity-induced polaritonic chemistry9.
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| 6. |
- Sundin, Elin, 1992, et al.
(author)
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Singlet Fission and Electron Injection from the Triplet Excited State in Diphenylisobenzofuran-Semiconductor Assemblies: Effects of Solvent Polarity and Driving Force
- 2020
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:38 Josef Michl Festschrift, s. 20794-20805
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Journal article (peer-reviewed)abstract
- Singlet fission has emerged as a promising way to overcome the Shockley-Queisser limit in solar energy conversion devices, and a few studies have claimed proof-of-principle results using dye-sensitized photoelectrodes. However, a detailed understanding of what factors govern the fate of the excited state on mesoporous surfaces is still lacking. Here, we have studied how the excitation progresses into singlet fission, electron injection, or formation of molecular charge separated states in diphenylisobenzofuran derivatives with flexible carbon linkers attached to nanocrystalline mesoporous ZrO2, TiO2, and SnO2 thin films. We show that singlet fission occurs for the molecule attached to ZrO2 films when the assembly is immersed in nonpolar solvents, and that singlet fission is hampered by the formation of a molecular charge separated state in more polar solvents. On TiO2 surfaces, direct electron injection from the singlet excited state outcompetes the singlet fission. Instead, triplet formation occurs via charge recombination from the conduction band of TiO2 in nonpolar solvents. When the molecule is attached to SnO2 films, singlet fission partly outcompetes electron injection from the singlet excited state and the two processes occur in parallel. Subsequent to singlet fission on SnO2, triplet injection into the conduction band of SnO2 is observed. The results presented here provide a detailed picture of the singlet fission dynamics in molecules attached to mesoporous semiconductor surfaces, demonstrating that both the semiconductor substrate as well as the environment around the molecules have a large impact, which can be useful in the design of future devices.
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| 7. |
- Buyukeksi, Sebile Isik, et al.
(author)
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Electron/energy transfer studies on hybrid materials based on dinuclear coordination compounds of twisted perylene diimide
- 2019
-
In: Journal of Photochemistry and Photobiology A: Chemistry. - : Elsevier BV. - 1010-6030. ; 372, s. 226-234
-
Journal article (peer-reviewed)abstract
- To understand the influence of transition metal ion coordination on the properties and performance of the triads, the symmetric bridging ligand, 1,10-phenanthroline-perylene diimide-1,10-phenanthroline, 1,10-Phen-PDI-1,10-Phen (1) comprising four electron-donating 4-methoxyphenoxy bulky groups at bay-positions and its corresponding square-planar coordination compounds with dichloroplatinum(II), [{PtCl2}(2)-1] (2) and palladium(II) [{PdCl2}(2)-1] (3) were prepared in order to tune the photochemical and optical properties of these hybrid materials. These triads show strong electronic absorption bands attributed to the PDI and M(II)(1,10-Phen)Cl-2 moieties in DMSO. UV-vis absorption spectra of the compounds were calculated using Time-Dependent Density Functional Theory (TDDFT) for the ground state optimized structures in DCM. Current results indicate that 2 has the lowest HOMO-LUMO gap (2.29 eV in DCM) among the investigated molecules. The energy and charge transfer processes with tailoring molecular structures are one of the important strategies for the design of future functional triads based on donor and acceptor moieties for hybrids optoelectronic devices. Thus, we studied linear absorption, fluorescence, and ultrafast transient absorption spectra measurements for the triads in DCM to investigate the impact of different functionalization strategies on the optical characteristics, photo-stability, and photo-induced charge-transfer (CT) processes. The observed ultrafast intramolecular charge transfer from donor units to acceptor part of 1-3 is related to fluorescence quenching and faster singlet state decay on transient absorption measurements. The intramolecular charge transfer mechanism was also compared with the unsymmetrical counterparts that were investigated previously. Symmetrical compounds exhibit faster charge transfer in comparison with the unsymmetrical compounds.
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| 8. |
- Canales Ramos, Adriana, 1993, et al.
(author)
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Self-Hybridized Vibrational-Mie Polaritons in Water Droplets
- 2024
-
In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 132:19
-
Journal article (peer-reviewed)abstract
- We study the self-hybridization between Mie modes supported by water droplets with stretching and bending vibrations in water molecules. Droplets with radii >2.7 μm are found to be polaritonic on the onset of the ultrastrong light-matter coupling regime. Similarly, the effect is observed in larger deuterated water droplets at lower frequencies. Our results indicate that polaritonic states are ubiquitous and occur in water droplets in mists, fogs, and clouds. This finding may have implications not only for polaritonic physics but also for aerosol and atmospheric sciences.
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| 9. |
- Dewambrechies, Adrián, et al.
(author)
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Enhanced Second-Order Nonlinearities at Strained Ultrasharp Zigzag Edges in Multilayer MoS 2
- 2023
-
In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:31, s. 15395-15405
-
Journal article (peer-reviewed)abstract
- Transition metal dichalcogenide (TMD) materials attract significant research attention thanks to their exceptional excitonic and optical properties. In this work, we analyze the formation of strained ultrasharp zigzag edges in MoS2 multilayers produced by anisotropic wet etching. The topography of the edges is determined by the relative stability of the different crystallographic directions of the multilayer as well as the interlayer interactions. Furthermore, we study the linear (Raman) and nonlinear (second-harmonic generation) spectroscopic characteristics of such edges and observe enhanced second-order nonlinearity originating from the strained zigzag edges. We also confirm that ultrasharp hexagonal nanoholes in MoS2 grow along the most stable crystallographic directions despite potential stacking faults or instabilities in the crystal quality. Our results open the way to exploit a broad range of phenomena occurring at the edges of MoS2 material, including the unique determination of crystal orientation for moiré engineering and strongly correlated phenomena in 2D material-based systems, as well as potential applications in TMD-based electrocatalysis and gas sensing.
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| 10. |
- Karatay, A., et al.
(author)
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Size and structure dependent ultrafast dynamics of plasmonic gold nanosphere heterostructures on poly (ethylene glycol) brushes
- 2017
-
In: Optical Materials. - : Elsevier BV. - 0925-3467. ; 73:NOV, s. 83-88
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Journal article (peer-reviewed)abstract
- We have investigated the plasmonic properties of heterostructures that consist of gold nanosphere (NSs) with average diameters of 60 nm, 40 nm and 20 nm on poly (ethylene glycol) (PEG) brushes by using ultrafast pump-probe spectroscopy experiments. Gold NSs start to behave like gold nanorods with increasing number of immobilization cycles due to the close proximity. Gold NSs immobilized by 3 and 5 deposition cycles show longitudinal modes of plasmon bands at long wavelengths which are characteristic behaviors for gold nanorods. Increasing the number of immobilization cycle also increase relaxation times of samples due to the close proximity. Linear absorption spectra and scanning electron microscopy images show that there are close packing assemblies for heterostructures containing 20 nm gold NSs as the small particle. Ultrafast electron transfer (
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| 11. |
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| 12. |
- Khalily, M. A., et al.
(author)
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Fabrication of Supramolecular n/p-Nanowires via Coassembly of Oppositely Charged Peptide-Chromophore Systems in Aqueous Media
- 2017
-
In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 11:7, s. 6881-6892
-
Journal article (peer-reviewed)abstract
- Fabrication of supramolecular electroactive materials at the nanoscale with well-defined size, shape, composition, and organization in aqueous medium is a current challenge. Herein we report construction of supramolecular charge-transfer complex one-dimensional (1D) nanowires consisting of highly ordered mixed-stack pi-electron donor-acceptor (D-A) domains. We synthesized n-type and p-type beta-sheet forming short peptide-chromophore conjugates, which assemble separately into well-ordered nanofibers in aqueous media. These complementary p-type and n-type nanofibers coassemble via hydrogen bonding, charge-transfer complex, and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This molecular design ensures highly ordered arrangement of D-A stacks within n/p-coassembled supramolecular nanowires. The supramolecular n/p-coassembled nanowires were found to be formed by A D-A unit cells having an association constant (K-A) of 5.18 x 10(5) M-1. In addition, electrical measurements revealed that supramolecular n/p-coassembled nanowires are approximately 2400 and 10 times more conductive than individual n-type and p-type nanofibers, respectively. This facile strategy allows fabrication of well-defined supramolecular electroactive nanomaterials in aqueous media, which can find a variety of applications in optoelectronics, photovoltaics, organic chromophore arrays, and bioelectronics.
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| 13. |
- Kücüköz, Betül, 1988, et al.
(author)
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Electron transfer reactions in sub-porphyrin-naphthyldiimide dyads
- 2019
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 21:30, s. 16477-16485
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Journal article (peer-reviewed)abstract
- A series of donor-acceptor compounds based on a sub-porphyrin (SubP) as an electron donor and naphthyldiimide (NDI) as an acceptor has been designed, synthesized and investigated by time-resolved emission and transient absorption measurements. The donor and acceptor are separated by a single phenyl spacer substituted by methyl groups in order to systematically vary the electronic coupling. The electron transfer reactions in toluene are found to be quite fast; charge separation is quantitative and occurs within 5-10 ps and charge recombination occurs in 1-10 ns, depending on the substitution pattern. As expected, when steric bulk is introduced on the adjoining phenyl group, electron transfer rates slow down because of smaller electronic coupling. Quantum mechanical modelling of the potential energy for twisting the dihedral angles combined with a simplified model of the electronic coupling semi-quantitatively explains the observed variation of the electron transfer rates. Investigating the temperature variation of the charge separation in 2-methyltetrahydrofuran (2-MTHF) and analyzing using the Marcus model allow experimental estimation of the electronic coupling and reorganization energies. At low temperature, relatively strong phosphorescence is observed from the donor-acceptor compounds with onset at 660 nm signaling that charge recombination occurs, at least partially, through the sub-porphyrin localized triplet excited state. Finally, it is noted that charge separation in all SubP-NDI dyads is efficient even at cryogenic temperatures (85 K) in 2-MTHF glass.
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| 14. |
- Kücüköz, Betül, 1988, et al.
(author)
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Quantum trapping and rotational self-alignment in triangular Casimir microcavities
- 2024
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In: Science advances. - 2375-2548. ; 10:17
-
Journal article (peer-reviewed)abstract
- Casimir torque, a rotational motion driven by zero-point energy minimization, is a problem that attracts notable research interest. Recently, it has been realized using liquid crystal phases and natural anisotropic substrates. However, for natural materials, substantial torque occurs only at van der Waals distances of ~10 nm. Here, we use Casimir self-assembly with triangular gold nanostructures for rotational self-alignment at truly Casimir distances (100 to 200 nm separation). The interplay of repulsive electrostatic and attractive Casimir potentials forms a stable quantum trap, giving rise to a tunable Fabry-Pérot microcavity. This cavity self-aligns both laterally and rotationally to maximize area overlap between templated and floating flakes. The rotational self-alignment is sensitive to the equilibrium distance between the two triangles and their area, offering possibilities for active control via electrostatic screening manipulation. Our self-assembled Casimir microcavities present a versatile and tunable platform for nanophotonic, polaritonic, and optomechanical applications.
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| 15. |
- Sakir, Menekse, et al.
(author)
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Fabrication of Plasmonically Active Substrates Using Engineered Silver Nanostructures for SERS Applications
- 2017
-
In: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 9:45, s. 39795-39803
-
Journal article (peer-reviewed)abstract
- Demanding applications in sensing, metasurfaces, catalysis, and biotechnology require fabrication of plasmonically active substrates. Herein, we demonstrate a bottom-up, versatile, and scalable approach that relies on direct growth of silver nanostructures from seed particles that were immobilized on polymer brush-grafted substrates. Our approach is based on (i) the uniform and tunable assembly of citrate-stabilized gold nanoparticles on poly(ethylene glycol) brushes to serve as seeds and (ii) the use of hydroquinone as a reducing agent, which is extremely selective to the presence of seed particles, confining the growth of silver nanostructures on the surface of the substrate. The diameter of the seed particles, concentration, as well as ratio of reactants and duration of the growth process are investigated for large-area growth of silver nanostructures with high surface coverage and plasmonic activity. The resulting silver nanostructures exhibit high levels of surface-enhanced Raman scattering activity at two different laser lines and allow detection of molecules at concentrations as low as 10 pM. The plasmonic properties of the silver nanostructures are further studied using ultrafast pump-probe spectroscopy. Spatially defined silver nanostructures are fabricated through the seed particles that are patterned via soft lithography, showing the capabilities of the presented approach in device applications.
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| 16. |
- Tutel, Yusuf, et al.
(author)
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Ultrafast electron/energy transfer and intersystem crossing mechanisms in bodipy-porphyrin compounds
- 2021
-
In: Processes. - : MDPI AG. - 2227-9717. ; 9:2, s. 1-11
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Journal article (peer-reviewed)abstract
- Meso-substituted borondipyrromethene (BODIPY)-porphyrin compounds that include free base porphyrin with two different numbers of BODIPY groups (BDP-TTP and 3BDP-TTP) were designed and synthesized to analyze intramolecular energy transfer mechanisms of meso-substituted BODIPY-porphyrin dyads and the effect of the different numbers of BODIPY groups connected to free-base porphyrin on the energy transfer mechanism. Absorption spectra of BODIPY-porphyrin conjugates showed wide absorption features in the visible region, and that is highly valuable to increase light-harvesting efficiency. Fluorescence spectra of the studied compounds proved that BODIPY emission intensity decreased upon the photoexcitation of the BODIPY core, due to the energy transfer from BODIPY unit to porphyrin. In addition, ultrafast pump-probe spectroscopy measurements indicated that the energy transfer of the 3BDP-TTP compound (about 3 ps) is faster than the BDP-TTP compound (about 22 ps). Since the BODIPY core directly binds to the porphyrin unit, rapid energy transfer was seen for both compounds. Thus, the energy transfer rate increased with an increasing number of BODIPY moiety connected to free-base porphyrin.
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| 17. |
- Zograf, Georgii, 1994, et al.
(author)
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Combining ultrahigh index with exceptional nonlinearity in resonant transition metal dichalcogenide nanodisks
- 2024
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In: Nature Photonics. - 1749-4893 .- 1749-4885. ; 18:7, s. 751-757
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Journal article (peer-reviewed)abstract
- Second-order nonlinearity in solids gives rise to a plethora of unique physical phenomena ranging from piezoelectricity and optical rectification to optical parametric amplification, spontaneous parametric down-conversion and the generation of entangled photon pairs. Monolayer transition metal dichalcogenides, such as MoS2, exhibit one of the highest known second-order nonlinear coefficients. However, the monolayer nature of these materials prevents the fabrication of resonant objects exclusively from the material itself, necessitating the use of external structures to achieve the optical enhancement of nonlinear processes. Here we exploit the 3R phase of a molybdenum disulfide multilayer for resonant nonlinear nanophotonics. The lack of inversion symmetry—even in the bulk of the material—provides a combination of massive second-order susceptibility, extremely high and anisotropic refractive index in the near-infrared region (n > 4.5) and low absorption losses, making 3R-MoS2 highly attractive for nonlinear nanophotonics. We demonstrate this by fabricating 3R-MoS2 nanodisks of various radii, which support resonant anapole states, and observing substantial (>100-fold) enhancement of second-harmonic generation in a single resonant nanodisk compared with an unpatterned flake of the same thickness. The enhancement is maximized at the spectral overlap between the anapole state of the disk and the material resonance of the second-order susceptibility. Our approach unveils a powerful tool for enhancing the entire spectrum of optical second-order nonlinear processes in nanostructured van der Waals materials, thereby paving the way for nonlinear and quantum high-index transition metal dichalcogenide nanophotonics.
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