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Transition from Two-photon Absorption to Saturable Absorption in Gold Patterned Ruby Thin Film
摘要： Nonlinear behaviour of gold micro disks patterned Ruby film has been investigated via Z-scan technique. Open Z-scan was performed for Ruby and Ruby/gold thin film using 532 nm Laser source. Two-photon absorption (TPA) and Saturable absorption (SA) have been observed in pure Ruby and Ruby/gold thin film respectively. The expression for normalized transmittance in open Z-scan was obtained by Gaussian decomposition method for fitting the open. The values for nonlinear absorption coefficient (β) for Ruby/gold (7.41 × 10?7??/??) was two orders of magnitude higher than that of Ruby (1.41 × 10?9??/??). Further, TPA and SA were confirmed by open Z-scan on these films, performed by 633 nm Laser source.
关键词： Surface Plasmon Resonance,Ruby,Z-scan,Two-photon absorption,Saturable absorption
更新于2025-09-23 15:22:29
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Systematic λ/21 resolution achieved in nanofabrication by two-photon-absorption induced polymerization
摘要： Photopolymerization, based on two-photon absorption in resins, has been recognized as one of the enabling technologies to fabricate three-dimensional micro/nanostructures with a sub-diffraction-limit resolution. This work focuses on improving the spatial resolution using femtosecond laser, λ=780 nm, with a systematic nanofabrication process which we developed. We discuss the factors influencing the spatial resolution, including the laser intensity, the exposure time, and the scanning speed by fabricating polymerized-voxels, nano-lines, and suspended nano-fibers in a photoresist based on a methyl-methacrylate monomer. We show that a resolution of ~36 nm, corresponding to ~λ/21, is achieved. Stable 3D microstructures can be fabricated by using our custom made set up.
关键词： Voxel,Resolution,Two Photon Polymerization,Micro/Nanostructures,Femtosecond Laser,Suspended Polymerized Fibers
更新于2025-09-23 15:22:29
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Hydrazine Exposé: The Next-Generation Fluorescent Probe
摘要： Hydrazine (N2H4) is one of the most important pnictogen hydride chemicals, and is utilized within a wide spectrum of industries. As a result of its extensive use, hydrazine’s monitoring methods have constantly come under fire due to its potential health risk and the subsequent environmental pollution. Fluorometric molecular sensing systems generally report with a major emphasis on the merit of fluorescence analysis. What we are proposing within this report is a next-generation fluorescent probe that allows hydrazine to become fully traceable, within multifarious environments that show fast and intuitional fluorescence transformation. A new sensing moiety, ortho-methoxy-methyl-ether (o-OMOM) incorporated electron donor (D)–acceptor (A) type naphthaldehyde provides high selectivity and sensitivity amidst its superiority within practical applications for sensing hydrazine. The new probe overcomes most of the drawbacks of currently used fluorescent probes, and due to its successful demonstrations, such as real-time spray-based sensing, soil analysis, and two-photon tissue imaging, its potential for practical application is beyond reproach.
关键词： fluorescent probe,chemical sensor,hydrazine,hydrazone-formation,two-photon tissue imaging
更新于2025-09-23 15:22:29
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Assessment of functionals for TDDFT calculations of one- and two-photon absorption properties of neutral and anionic fluorescent proteins chromophores
摘要： Performance of DFT functionals with different percentage of exact Hartree-Fock exchange energy (EX) is assessed for recovery of the CC2 reference one- (OPA) and two-photon absorption (TPA) spectra of fluorescent proteins chromophores in vacuo. The investigated DFT functionals, together with their EX contributions are: BLYP (0%), B3LYP (20%), B1LYP (25%), BHandHLYP (50%) and CAM-B3LYP (19% at short range and 65% at long range). Our test set consists of anionic and neutral chromophores as naturally occuring in the fluorescent proteins. For the first time, we compare TDDFT and CC2 methods for higher excited states, than the S1 state, exhibiting relatively large TPA intensity. Our TDDFT results for neutral chromophores reveal an increase of excitation energies as well as TPA and OPA intensities errors, compared to CC2-derived results, as the DFT functional contains less exact exchange. The long-range-corrected CAM-B3LYP functional performs the best, closely followed by BHandHLYP, while BLYP usually significantly underestimates all investigated spectral properties, hence being the worst in reproducing the reference CC2 results. The hybrid B3LYP and B1LYP functionals can be roughly placed in between. We propose that TDDFT may underestimate the TPA intensities for neutral chromophores of fluorescent proteins due to underestimated oscillator strengths between some excited states. In case of anionic chromophores, we find that B3LYP and B1LYP functionals overcome others in terms of reproducing CC2 excitation energies. On the other hand, however, TPA intensity is usually significantly underestimated and in this respect CAM-B3LYP functional seems to be again superior. In contrast to the case of neutral chromophores, it seems that large magnitude of excited-state dipole moment or change in dipole moment upon excitation may be the driving force behind high TPA transition moments.
关键词： fluorescent proteins chromophores,one-photon absorption,DFT functionals,two-photon absorption,TDDFT,CC2
更新于2025-09-23 15:21:21
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Formation of Occupied and Unoccupied Hybrid Bands at Interfaces between Metals and Organic Donors/Acceptors
摘要： Efficient charge transport in organic semiconductors and at their interfaces with electrodes is crucial for the performance of organic molecule-based electronic devices. Band formation fosters effective transport properties and can be found in organic single crystals of large π-stacking aromatic molecules. However, at molecule/metal interfaces hybrid band formation and band dispersion is a rarely observed phenomenon. Using angle-resolved two-photon photoemission supported by density functional theory calculations we demonstrate such band formation for two different molecule/metal systems, namely tetrathiafulvalene (TTF)/Au(111) and tetrafluoro-tetracyanoquinodimethane (F4TCNQ)/Au(111), in the energy region of occupied as well as unoccupied electronic states. In both cases strong adsorbate/substrate interactions result in formation of interface states due to hybridization between localized molecular states and delocalized metal bands. These interface states exhibit significant dispersions. Our study reveals that hybridization in combination with an extended well-ordered adsorption structure of the π-conjugated organic molecules is a striking concept to receive and experimentally observe band formation at molecule/metal interfaces.
关键词： band formation,organic semiconductors,molecule/metal interfaces,hybridization,charge transport,density functional theory,angle-resolved two-photon photoemission
更新于2025-09-23 15:21:21
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Robust Wavelength-Converting and Lasing Media from Wafer-Scale Inorganic Perovskites Enabled by a Protective Surface Layer
摘要： Despite that the inorganic halide perovskites show great promise in wavelength-conversion and lasing applications, the stability and scalability remain as the obstruction toward practical applications. Herein, we, for the first time, employ the wafer-scale inorganic perovskite single crystals to address the above issue. Our spectroscopic analysis reveals that the carrier trapping on the crystal surface is the most probable culprit to hinder the optical amplification for the weak-penetrating one-photon pumping, whilst, the interior of the crystal preserves intact and show low-threshold stimulated emission by two-photon absorption in the near infrared regime. Thanks to the effective protection from the surface layer, the stimulated emission maintains 90% of the initial intensity upon uninterrupted pumping of 4 hours and shows nearly constant threshold upon long-term storage without any encapsulation (> one year). By exploiting a parallel-mirror cavity, an optically pumped wavelength-converting and laser device featuring a spatially coherent output beam is constructed. Our finding greatly advances the development of practical coherent light sources based on halide perovskites.
关键词： wavelength-conversion,lasing,scalability,two-photon absorption,inorganic halide perovskites,stability,coherent light sources,stimulated emission
更新于2025-09-23 15:21:01
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Highly Conjugated, Fused-Ring, Quadrupolar Organic Chromophores with Large Two-Photon Absorption Cross-Sections in the Near-Infrared
摘要： The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 103 GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10-21 m2) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.
关键词： pump-probe spectroscopy,Nonlinear optics,Z-scan,organic optoelectronics,ultrafast spectroscopy,two-photon absorption
更新于2025-09-23 15:21:01
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Viscosity Measurements Using a Two-photon Ratiometric Fluorescent Sensor with Two Rotors
摘要： A new ratiometric two-photon fluorescence sensor, Qca-Cy2, comprised of a hybrid cyanine–carbazole platform with two rotating sites is described. Qca-Cy2 can report on mitochondrial viscosity within live cells, as well as in living tissues at depths of 50-130 μm by ratiometric fluorescence imaging using two-photon microscopy.
关键词： ratiometric,viscosity measurements,fluorescent sensor,mitochondrial viscosity,two-photon
更新于2025-09-23 15:21:01
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Deuterium Kinetic Isotope Effect in the Photocatalyzed Dissociation of Methanol on TiO2(110)
摘要： Deuterium kinetic isotope effect (KIE) in the photochemistry of methanol on TiO2(110) has been studied to find the rate-determining step (RDS) and understand the reaction mechanism using two-photon photoemission spectroscopy (2PPE). Deuterium substitution of the methyl hydrogen has little effect on the kinetics of this reaction, suggesting that neither the break of the C-H(D) bond nor the transfer of H(D) atoms to the bridging sites is the RDS in the transformation of methanol into formaldehyde. In contrast, the reaction rate of MeOH is ~1.3 times of that of MeOD, suggesting that the cleavage of O-H(D) is the RDS in the photocatalyzed dissociation of methanol on TiO2(110). The results contradict with the common fact that C-H(D) is more difficult to break than O-H(D) based on ground state energetics, implying the involvement of photogenerated charge carriers in the reaction of C-H break whereas the cleavage of O-H is likely a thermal reaction. Difference in the activation energy of O-H and O-D dissociation reaction in the methanol/TiO2(110) system has been calculated based on the KIE measurements. Our work is consistent with the fact that methoxy is photocatalytically more reactive than methanol, and suggests that the conversion of methanol into methoxy is crucial in the photochemistry of methanol on TiO2(110) and probably other metal oxide semiconductor surfaces.
关键词： two-photon photoemission spectroscopy,photocatalyzed dissociation,Deuterium kinetic isotope effect,TiO2(110),methanol
更新于2025-09-23 15:21:01
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2PPE spectroscopy of unoccupied electronic states at CuPc/PTCDA/Ag(111) interfaces
摘要： The unoccupied electronic structure of stacked layers of copper(II)phthalocyanine (CuPc) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on Ag(111) has been investigated by means of two-photon photoemission (2PPE). We find a rich electronic structure comprising at least five unoccupied electronic states which we identify based on their energetic position and their dispersion in momentum space. More specifically, we observe the first and the second image-potential states of the modified Ag(111) surface, as well as the metal–organic interface state (IS) inherent to the PTCDA/Ag(111) interface. Moreover, two additional molecular features are observed for the CuPc/PTCDA/Ag(111) system which we attribute to an unoccupied molecular orbital (LUMO+2) of CuPc. The 2PPE intensity of the IS exhibits a pronounced dependence on the pump photon energy, which closely follows the optical absorption of the outer molecular layer. This strongly points to charge transfer from the optically excited molecules to the interface state.
关键词： charge transfer,PTCDA,metal–organic interfaces,CuPc,organic heterosystems,two-photon photoemission
更新于2025-09-23 15:21:01