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Broadband reverse saturable absorption is systematically investigated via Z-scan, transient absorption spectrum (TAS). The excited state absorption and negative refraction of Orange IV are observed in the Z-scan experiment at 532 nm. Meanwhile, two-photon-induced excited state absorption and pure two-photon absorption are observed at 600 nm and 700 nm with the pulse width of 190 fs, respectively. An ultrafast broadband absorption in the visible wavelength region is observed via TAS. The different nonlinear absorption mechanisms at multiple wavelengths are discussed and interpreted from the results of TAS. In addition, the ultrafast dynamics of negative refraction in the excited state of Orange IV are investigated via a degenerate phase object pump-probe, from which the weak long-lived excited state is extracted. All studies indicate that Orange IV has the potential to be further optimized into a superior broadband reverse saturable absorption material and also has certain reference significance for the study of optical nonlinearity in organic molecules containing azobenzene groups.

The emission linewidth of quantum dots (QDs) is one of the important optical properties, which is essential for the applications of QD lasers, high-quality displays, and biological imaging. However, we know less about controlling emission linewidth and its underlying mechanisms. Here we introduce a wurtzite ZnSe shell onto a wurtzite CdSe core to produce asymmetric strain due to their large, anisotropic lattice mismatch. Such asymmetric pressure induces significant splitting (Δ

CuI is one of the promising hole transport materials for perovskite solar cells. However, its tendency to form defects is currently limiting its use for device applications. Here, we report the successful improvement of CuI through Sn doping and the direct measurement of the carrier relaxation and interfacial charge-transfer processes in Sn-doped CuI films and their heterostructures. Femtosecond-transient absorption (fs-TA) measurements reveal that Sn doping effectively passivates the trap states within the bandgap of CuI. The

Optical limiting (OL) is an important application of nonlinear optics. Summarizing the structure-property relationship of organic materials is an effective means to develop superior optical limiters. In this work, two triphenylamine-based chalcone derivatives

The introduction of a double 1,3-butadiyne bridge greatly enhances the ultrafast broadband reverse saturable absorption of twistacene.

Multidentate organic ligands 3,5-bis(4-pyridyl)pyridine (dpypy) and 1,2,4,5-tetrakis(4-pyridyl)benzene (tpb) are first exploited to construct cluster-containing metal–organic frameworks (C-MOFs). T...

An ultrathin multilayer film with well-defined structure containing anionic Poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) and ...

We report the fabrication of amorphous zinc tin oxide (ZTO) thin films using rf magnetron sputtering and rapid postannealing. A vertically graded composition alloy (Zn1–xSnxO) is constructed in a s...

Two atom-precise silver nanoclusters [Ag25Cl2(Tab)14(PhCOO)11(DMF)4](PF6)12 (Ag25, DMF=N,N-dimethylformamide) and [Ag26Cl2(Tab)14(PhCOO)13(DMAc)4](PF6)11(Ag26, DMAc=N,N-dimethylacetamide) were synthesized based on the electrically neutral thiolate protective ligand, 4-(trimethylammonio)benzenethiolate (Tab). The weak Ag-S interaction in Tab-protected silver nanoclusters allows to insert or leave a single silver atom in the Ag-S skeleton through solvent-trigger core fragmentation and re-arrangement, thereby realizing the reversible conversion of Ag25 and Ag26 for the first time.

This work exposes for the first time the remarkable influence of intramolecular group rotation on third-order nonlinear optical (NLO) performance. In order to prove the role of group rotation, we designed and synthesized two photo-response compounds tetramethyl 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis (methylene)) diisophthalate (1) and 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis (methylene)) diisophthalic acid (2) and investigated their NLO performance under different substituent (benzyloxy group) rotation states. 1 and 2 have dynamic benzyloxy group rotation in dilute solution and shows reverse saturated absorption (RSA). When the benzyloxy group rotation of 1 and 2 was restricted by PMMA, their NLO performance not only converted into saturated absorption (SA) and NLO refraction behaviours, but also hardly changed after isomerization. Interestingly, we also restricted the benzyloxy group rotation in solution to a certain extent through photo-induced trans → cis isomerization, and found that the NLO performances of cis isomers of 1 and 2 exhibit SA and positive refraction and are similar to those of 1 -PMMA and 2 -PMMA. This work provides a new exploratory method for studying the influencing factors of third-order NLO performance.

Two pyrenyl Schiff base derivatives with π conjugated structures (

Na

The third-order nonlinear optical properties of A–D–A structural molecules which are originally used as acceptors in organic photovoltaic (OPV) devices were investigated in solution and film to deeply understand the molecular conformation–property relationship. Firstly, a planar structure (O-IDTBR) bearing the indacenodithiophene (IDT) core and a twisted molecule (IDFBR) comprising the indenofluorene (IDF) core, which possess identical acceptor units, were measured by the Z-scan technique at the near-infrared region in toluene solution. O-IDTBR exhibits a more superior TPA cross section than IDFBR in the range of 800–1030 nm (ca. 1497–8811 GM). In particular, the TPA cross section of the planar configuration is 8811 GM, over 4 times that of the twisted molecule at 800 nm. Secondly, their corresponding spin-coating films are investigated via a 4f coherent imaging experiment at 532 nm. It is noticeable that the nonlinear refractive index of the planar molecule is up to 2.09–2.15 × 10−15 m2 W−1, which is nearly 5 times that of IDFBR. The dynamic processes and morphologies of films are systematically characterized by transient absorption spectroscopy and AFM. The investigations present a better understanding of the structure–property relationship of the A–D–A conjugated materials which are believed to have promising NLO application in the future.

A novel fluorenone derivative, FO52, is designed and synthesized. The fluorenone group is introduced to provide the central π-conjugated system in the molecule and triphenylamine is substituted at both sides. Intramolecular Charge Transfer (ICT) from the terminal groups to the molecular center is confirmed via DFT calculations. Ultrafast optical nonlinearities are investigated via Z-scan and transient absorption spectroscopy (TAS) studies with a 190 fs laser. Reverse saturable absorption, two-photon induced excited-state absorption, and pure two-photon absorption are observed at 532 nm, 650 nm, and 800 nm, respectively. The different mechanisms at these wavelengths are discussed and interpreted with assistance from the results from TAS. Furthermore, strong excited-state refraction and ultrafast negative refraction from the bound electron response are resolved and discussed in phase object pump probe (POPP) experiments. The results suggest that the ICT-enhanced optical nonlinearities provide FO52 with strong optical limiting capabilities at visible wavelengths and ultrafast refraction with tiny attenuation in the near infrared region. The combination of these properties in one compound could be attractive for applications like laser protection and low-loss all-optical switching.

Herein, we report a novel graphene oxide (GO) nanohybrid covalently functionalized by covalent organic polymer (COP) based on porphyrin (GO-TPPCOP), as the optical limiter and hydrogen evolution reaction (HER) electrocatalyst. The GO-TPPCOP nanohybrid exhibits markedly enhanced optical limiting and HER activity over that of TPP, GO and TPPCOP alone. More importantly, the optical limiting property and HER activity of GO-TPPCOP nanohybrid are comparable to the state-of-the-art activity of materials from some previous reports. The possible mechanisms of optical limiting and HER are explored by various means, including UV-Vis absorption, fluorescence, photocurrent, electrochemical impedance spectra and Raman spectroscopic techniques. It is demonstrated that the synergistic effect and charge transfer between GO and TPPCOP are important factors in determining its optical limiting and HER performances. These results demonstrate a new strategy to design and develop functional nanohybrids for efficient optical limiting and HER activity by the covalent linkage of GO with COPs.

The treatment of the metal sulfide precursor [Et4N][Tp*WS3] (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) (1) with Cu(I) and the Fe-bipyridine complex ligand L1 in the presence of (NH4)2SO4 produced one-dimensional (1D) [(Tp*WS3Cu2)2(L1)2](BF4)2 (2) and two-dimensional (2D) [(Tp*WS3Cu3)2(L1)3(μ3-SO4)2] (3) heterometallic coordination polymers (CPs). Both CPs were characterized using elemental analysis, IR spectra, UV-vis spectra, mass spectra and single crystal X-ray diffraction. Compound 2 contains a butterfly-shaped core [Tp*WS3Cu2] serving as a two-connecting node to link its equivalent ones viaL1 bridges to form a 1D zigzag chain extending along the c axis. Compound 3 consists of a 2D layer structure with a (6,3) network in which each complete cubane-like core [Tp*WS3Cu3(μ3-SO4)] works as a pyramidal three-connecting node to link its equivalent ones viaL1 bridges. The formation of the different structural topologies of 2 and 3 may be ascribed to the different precursor-to-Cu(I) molar ratios (1 : 2 for 2 and 1 : 3 for 3). The cluster modular construction (CMC) was used to simplify the structural modules of 2 and 3 as straightforward modules to clarify the possible process of assembly and structural characteristics. In addition, the third-order nonlinear optical (NLO) properties of 2 and 3 in MeCN were investigated. They both displayed enhanced third-order NLO responses relative to those of 1 and L1.

Three cross-conjugated chalcone derivatives T3CT, T3CP2, and T3CP3 were designed and synthesized to develop excellent organic nonlinear optical (NLO) materials. In a Z-scan experiment, all compounds show good NLO absorption characteristics in the visible to near-infrared region. The photophysical mechanism is confirmed to be two-photon absorption (TPA)-induced excited-state absorption (ESA). Intramolecular charge transfer (ICT) observed in transient absorption spectra (TAS) significantly affects molecular NLO properties. We define the π-conjugated system that dominates the electron transition process in the cross-conjugated structure as the effective π-conjugated structure. Electron transition analysis shows a sufficiently strong ICT can effectively expand the effective π-conjugated structure in these cross-conjugated structures. The TPA cross sections of these compounds at 650 and 750 nm are only in the range of 17-97 GM. However, we achieve a significant enhancement of the TPA cross section at 580 nm (1737-2027 GM) by extending the effective π-conjugated structure. Excited by 580 nm femtosecond laser pulses, all compounds exhibit excellent OL performance and the minimum OL threshold is 4.71 × 10-3 J/cm2. The results show that these cross-conjugated chalcone derivatives have promising applications in OL, and their NLO performance can be effectively improved by modulating the effective π-conjugated structure.

Phase (composition) is known to play a key role in determining the electronic and optical properties of amorphous oxide semiconductors. In this work, modulating the ultrafast nonlinear optical (NLO) response of SnO2 and SnO thin films by tuning oxygen partial pressure during film sputtering is explored. Femtosecond Z-scan results demonstrate that intermediate phases have no profound impact on the two-photon absorption (TPA) response of SnO2 and SnO films. Interestingly, the magnitude of the effective nonlinear absorption coefficient (βeff) of both intermediate SnO2-x and SnOx are enhanced after the change of Sn2+/Sn4+ composition ratio, as measured by picosecond Z-scan technique. Femtosecond degenerate pump-probe measurements show that intermediate phases accelerate the carrier trapping and improve the defect-related carrier absorption in SnOx (SnO-rich) film, while intermediate phase suppress the TPA response of SnO2-x (SnO2-rich) films, therefore carrier-induced absorption dominates the NLO behavior of SnO2-x film on picosecond regime. Our results indicate a simple and effective way to modulate the NLO response of transparent conductive oxide SnO2 and SnO.

The process and condition of saturable absorption (SA) and reverse saturable absorption (RSA) of ultrafast nonlinear optics in metal nanoparticles are essential for applications including light generation, amplification, modulation, and switching. Here, we first discover and explore the multiple transformations (SA-RSA-SA) of ultrafast nonlinear absorption behavior of metal nanoparticles in femtosecond pulses. Correspondingly, the energy level model and fitting formula of multiple transformations are established to illustrate the process of optical response. The femtosecond transient absorption spectra provide information about their ultrafast dynamics process and vibrational mode, which further reveals the multiple transformation mechanisms of nonlinear absorption in gold nanobipyramids (Au-NBPs). Furthermore, Au-NBPs exhibit a significantly higher SA modulation depth up to 42% in the femtosecond, which is much higher than the reported values of other nanomaterials. Our results indicate that Au-NBPs can be used as broadband ultrafast Q-switching and mode-locking, and the conversion offers new opportunities for metal nanostructures in applications of optical switching.

The third-order nonlinear optical (NLO) materials with stimuli-responsive properties have received extraordinary attention due to their controllable photophysical properties. In this work, two attractive metal complexes third-order NLO switches, which are far superior to congeneric optical switches in terms of their performance conversion, versatility, and fast response, were successfully designed and synthesized. The test of their third-order NLO properties proves that the metal complexes exhibit reverse saturable absorption and self-defocusing refraction. After light irradiation, the third-order NLO behavior turns quickly into self-focusing refraction. The relation between the molecular structures and the third-order NLO properties was investigated via1H nuclear magnetic resonance and ultraviolet-visible absorption. The results show that the metal ions have a significant influence on the NLO behavior and reveal the origin of third-order NLO properties via Z-scan determinations, pump-probe technology, and density functional theory calculations. These metal complexes can be used as third-order NLO switches with excellent fatigue resistance and broaden the application range of third-order NLO materials with adjustable performances.

Twisted intramolecular charge transfer (TICT) process endow the luminogens containing rotatable electron donor-π-acceptor (D-π-A) structure with abundant electronically excited states, resulting in multiple photophysical properties. In this work, a new propeller-like molecule of 5,6-di(4-N,N-(dimethylamino)phenyl)pyrido[2,3-b]pyrazine (APPP) with rotatable D-π-A structure was facilely prepared, which exhibited typical TICT character. Interestingly, aggregation/viscosity-induced emission and third-order nonlinear optical (NLO) signal inversion from reverse saturation absorption to saturation absorption in aggregated state or solutions with high viscosity were observed in this system. Mechanism study showed that these properties were originated from the restricted intramolecular rotation (RIR) process, which not only cut off the non-radiative transition channel of excited electron but also influenced the excited electron transition rate from charge transfer (CT) state to TICT state. According to these results, a temperature-triggered third-order NLO optical switch was successfully designed. This work affords a new type of aggregation-induced emission luminogen (AIEgen) with third-order NLO properties, and more importantly, provides a visualized prototype to understand the origination of third-order NLO properties in TICT systems.

As laser technology advances, the importance of laser protection puts an urgent demand for robust and high-efficient optical limiting materials. In this work, CsPbX3 (X = Cl/Br, Br) NCs were synthesized by precisely controlling the ratio of Cl− to Br− and the heat treatment temperature, and the third-order nonlinear (TONL) optical properties of them were investigated systematically and deeply based on a nonlinear optical imaging technique with the phase-object (NIT-PO) at 532 nm for the first time. All of them demonstrate strong reverse saturation absorption (∼10-12–10-11 m/W), and the sign of TONL refraction index (γ) relates to the component (CsPb(Cl/Br)3 NCs glasses: ∼10-20 m2/W, CsPbBr3 NCs glasses: ∼−10-20 to 10-19 m2/W). In addition, they have excellent characteristics of thermal stability and water stability, as well as photostability under 455 nm laser irradiation, indicating that it is a promising optical limiting material.