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International audience; The study of nonlinear optics in the 1960s attracted considerable attention from a theoretical standpoint, engendering many proposals for practical use of these new photonic effects. Among these suggestions, the development of efficient two-photon absorption (2PA) has attracted sustained interest due to its demonstrated (or potential) use in a broad range of applications that include optical data storage, optical limiting and nanofabrication. The use of 2PA in biological applications is particularly appealing. This is because 2PA offers several advantages for biooriented applications, such as intrinsic three-dimensional resolution, increased penetration depth in biological materials such as tissue and highly focused excitation at half-energy, leading to a decrease of auto-fluorescence and photodamage. In this Primer Review, we introduce the essential background theory needed for an understanding of the field, we describe the key experiments deployed to quantify material performance, we discuss the evolution of 2PA molecular design, and we summarise the state-of-the-art and the existing challenges in the use of 2PA in imaging, therapy and theranostics.

A novel passivation strategy via the coordination between porphyrin derivatives and perovskite ionic defects is reported and demonstrated to enhance the nonlinear optical performance of perovskite materials.

A covalently-linked SnS2–Por nanohybrid with enhanced optical limiting performance is reported. The boost in optical limiting can be attributed to the effective charge transfer between the SnS2 nanosheets and the grafted porphyrin moieties.

Surface terminations of two-dimensional materials should have a strong influence on the nonlinear optical (NLO) properties, but the relationship between surface terminations and NLO properties has not yet been reported. In this work, switching the NLO properties of MXenes (Ti

A wide bandgap is an essential requirement for a nonlinear optical (NLO) material. However, it is very challenging to simultaneously engineer a wide bandgap and a strong second-harmonic generation (SHG) response, particularly in NLO materials containing second-order Jahn-Teller (SOJT) distorted units. Herein, we employ a bandgap engineering strategy that involves the dual fluorination of two different types of SOJT distorted units to realize remarkably wide bandgaps in the first examples of 5d

In situ electrochemical activation results in high-valent metal compounds (with a composite of Co3O4 and TiO2 as a prototype) that exhibit outstanding catalytic performance in the alkaline HER.

The first covalently functionalized example of TiS2 nanosheets with tetraphenylporphyrin featuring efficient intrahybrid energy transfer and therefore enhanced saturation absorption.

Three tridentate Schiff base ligands were synthesized from the reactions between 2-picolylamine and salicylaldehyde derivatives (3-ethoxy (OEt), 4-diethylamino (NEt2) and 4-hydroxy (OH)).

A more conjugated nanocomposite and a potential NLO candidate with a strong intrasystem interaction were constructed using a rarely mentioned porphyrin dimer and graphene.

Polar Ce3F4(SO4)4, which possesses a strong SHG effect and sufficient birefringence, was rationally designed through fluorination degree modulation.

Covalent functionalization of Ti3C2Tx nanosheets with fullerenes C60 and C70 for enhanced optical limiting performance across spectral and temporal domains was carried out for the first time.

Deep-ultraviolet (deep-UV) nonlinear optical (NLO) crystals are key materials in creating tunable deep-UV lasers for frequency conversion technology. However, practical application of the sole usable crystal, KBe2 BO3 F2 , has been hindered by the high toxicity of beryllium and its layering tendency in crystal growth. Herein, we report a beryllium-free deep-UV NLO material NaSr3 (OH)(B9 O16 )[B(OH)4 ] (NSBOH), synthesized by a covalent bond modification strategy under hydrothermal conditions. Moisture-stable NSBOH exhibits strong second-harmonic generation (SHG) at 1064 nm (3.3 × KH2 PO4 ) and 532 nm (0.55 × β-BaB2 O4 ), both amongst the largest powder SHG responses for a deep-UV borate, with good phase-matchability and a short wavelength cutoff edge (below 190 nm). NSBOH possesses a 3D covalent anionic [B9 O19 ]∞ honeycomb-like framework with no layering. The Sr2+ and Na+ ions, residing in the cavities of the anionic framework, act as templates for the assembly and favorable alignment of NLO-active groups, resulting in an optimal balance between strong SHG activities and wide UV transparency. These merits indicate NSBOH is a very attractive candidate for deep-UV NLO applications.

Second-harmonic-generation (SHG) efficiency and birefringence are two crucial parameters for nonlinear optical (NLO) crystals. However, the simultaneous optimization of these two key parameters rem...

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d0-transition-metal (TM) tellurite with half of the d0-TM-octahedra partially fluorinated, namely, quinary RbTeMo2O8F, which exhibits giant SHG responses (27 times that of KH2PO4 (KDP) and 2.2 times that of KTiOPO4 (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo2O8F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 μm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO5F]/[MoO6] octahedra and the seesaw-like [TeO4], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO6] octahedra.

Functional materials displaying large ultrafast third-order optical nonlinearities across a wide spectral region and broad temporal domain are required for all-optical signal processing. Particularly desirable is nonlinear optical (NLO) activity at near-infrared (NIR) wavelengths with femtosecond pulses. Herein the first triply-fused porphyrin dimer (TFP)-functionalized single-walled carbon nanotube (SWCNT) nanohybrid was successfully constructed by covalently grafting TFPs onto SWCNT. The results of Z-scan techniques demonstrate that the newly obtained TFP-SWCNT nanohybrid was found with a strong NLO performance under both nanosecond and femtosecond irradiation. In the nanosecond regime, an enhancement in optical limiting (OL) of the TFP-SWCNT nanohybrid is seen at 532 nm when compared with the performance of porphyrin monomer-functionalized SWCNT nanohybrid Por-SWCNT. Under femtosecond irradiation, the TFP-SWCNT nanohybrid exhibits a particularly strong OL effect with a giant two-photon absorption (TPA) cross section value (ca. 15,500 GM) at 800 nm pulses that mainly stems from intense TPA of TFP, in sharp contrast to the Por-SWCNT nanohybrid which exhibits only saturable absorption under identical irradiation. These results demonstrate that the newly-developed TFP-SWCNT nanohybrid is a very promising OL candidate for practical applications across wide spectral and temporal domains, and that covalently functionalizing carbon-based materials with triply-fused chromophores may be a useful approach to engineering adaptable photonic devices with broad-ranging NLO activity.

The syntheses of [Cu(PPh3)2(L)]NO3 and [Cu(PPh3)2(L-SO3Na)]NO3 were achieved through the reaction of Cu(PPh3)2NO3 and equimolar amount of the ligands (L = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine; LSO3Na = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine-4,4′-disulfonic acid disodium salt). The complexes were characterized by NMR and IR spectroscopy and mass spectrometry. The compounds exhibit similar absorption and emission spectra, suggesting a similar electronic structure. Ct-DNA binding studies show the strong influence of the net charge as Cu-L (positively charged) is able to bind to ct-DNA while Cu-LSO3Na (negatively charged) is not. The net charge of the complexes affects the thermodynamic and kinetic binding parameters toward human serum albumin. HSA-binding of the complexes was further investigated by molecular docking, revealing different binding sites on the HSA protein as a function of the net charge. The different anticancer activities of the complexes towards ovcar-3 and hope-62 cancer cell lines are suggestive of a role for the overall charge of the complexes. Interaction with the DNA is not the major mechanism for this class of complexes. The overall net charge of the pharmacophore (anticancer agent) should be a key consideration in the design of anticancer metal complexes.

This research was financially supported by the NationalNatural Science Foundation of China (nos. 51432006,52002276), the Ministry of Education of China for theChangjiang Innovation Research Team (no. IRT14R23), theInnovation Program of Shanghai Municipal Education Com-mission, and the Ministry of Education and the StateAdministration of Foreign Experts Affairs for the 111 Project(no. B13025). M.G.H. thanks the Australian Research Coun-cil for support (DP170100411).

This research was financially supported by the National Natural Science Foundation of China (No. 51432006), the Ministry of Education of China for the Changjiang Innovation Research Team (No. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (No. B13025), and the Innovation Program of Shanghai Municipal Education Commission. M.G.H. and C.Z. thank the Australian Research Council for support (DP170100411).

Multi-photon absorption (MPA) is of increasing interest for applications in technologically important "windows" of the electromagnetic spectrum (near-infrared III, NIR-III, 1550-1870 nm; and the new 2080-2340 nm region); however, few molecules exist that display strong MPA at these long wavelengths. We herein report the syntheses of the first 2,5,8-s-heptazine-cored organometallic complexes, together with organic analogues. The complexes exhibit outstanding 3PA cross-sections in the NIR-III and exceptional 4PA cross-sections in the new 2080-2340 nm window. We demonstrate that replacing organic donor groups by organometallic units results in an order of magnitude increase in 3PA, the "switching on" of 4PA, and a dramatic improvement in photo-stability. Our results highlight the impressive outcomes possible with an "organometalation" approach to NLO materials design.

Materials capable of generating coherent short-wave (

Ultraviolet (UV) nonlinear optical (NLO) materials possess important practical applications in modern laser science and technology, which are attracting significant research interest in the fields of chemistry, physics and materials science. A fluorinated mixed main-group metal sulfate and its defluorinated analogue, Rb2InF3(SO4) (RIFSO) and Rb3In(SO4)3 (RISO), were designed and synthesized for NLO study via mild hydrothermal methods. RIFSO unfortunately crystallizes in centric space group Pbcn (no. 60) while RISO crystallizes in acentric space group R3c (no. 161). Both of them exhibit a one-dimensional chain structure composed of corner-shared [InO2F4] or [InO6] and [SO4] groups. Optical property studies reveal that RISO displays a large band gap (5.75 eV) corresponding to a short UV cut-off edge (215 nm), a moderate second harmonic generation (SHG) efficiency of ∼0.5 times that of KH2PO4 (KDP) with phase-matchable performance, and high thermostability (>800 °C), demonstrating its potential as an applicable UV NLO material. First-principles calculations have been performed to further elucidate the structure–property relationship of RISO.

Room-temperature phosphorescent (RTP) materials with long luminescence lifetimes have stimulated considerable interest. However, pure organic molecules with persistent room-temperature phosphorescence are still rarely reported. In this work, we study two molecules, DCzMPh and TCzMPh, in which persistent room-temperature phosphorescence in the amorphous state is achieved via the heavy-atom effect of bromine atoms in their structure. Their final quantum yields are found to be as high as 90 and 93%, respectively, at the phosphorescence lifetimes of 0.27 and 0.28 s, respectively. Moreover, both molecules are shown to be appropriate for security protection applications.

The first fluorinated lead vanadate selenite Pb2(V2O4F)(VO2)(SeO3)3 (PVOFS) was successfully synthesized via a mild hydrothermal method. This compound crystallizes in the chiral space group P212121 of the orthorhombic system and it is the first noncentrosymmetric structure in the PbII–VV–SeIV–O–F system. PVOFS is composed of five kinds of second-order Jahn–Teller susceptible asymmetric motifs, including three distinct types of vanadium-centered polyhedral units ([VO5F], [VO6] and [VO5]), [SeO3] pyramids and Pb2+ cations. It features a unique three-dimensional open framework structure displaying three types of tunnels (10-, 8- and 7-membered rings), which enriches the structural diversity for fluorinated vanadate selenite systems. Optical property studies revealed that PVOFS shows a second-harmonic generation response of 0.3 times that of the commercial KH2PO4 with phase matching behavior, a wide transparent region covering IR windows, an optical band gap of 2.35 eV, a high laser damage threshold of 61 times that of AgGaS2, and a large birefringence of 0.105 at 1064 nm. Theoretical calculations have been performed to clarify the correlation between the molecular structure and the optical properties of PVOFS.

The first alkali–metal selenate nonlinear optical (NLO) crystal, Na5(SeO4)(HSeO4)3(H2O)2, has been obtained by in situ hydrothermal synthesis. It crystallizes in the polar and noncentrosymmetric (NCS) space group Cc (no. 9). The structure of Na5(SeO4)(HSeO4)3(H2O)2 can be described as isolated [SeO4]/[HSeO4] tetrahedra connected by H-bonding interactions and Na–O bonds, forming a three-dimensional framework. Powder second-harmonic generation (SHG) measurements show that Na5(SeO4)(HSeO4)3(H2O)2 is phase-matching with a moderate SHG response of ca. 1.6 times that of benchmark KH2PO4. The UV-Vis-NIR spectrum shows that the title compound is a wide-band semiconductor with an optical band gap of 3.57 eV. The birefringence of Na5(SeO4)(HSeO4)3(H2O)2 was calculated to be 0.037 at 1064 nm. First-principles studies show that the [SeO4]/[HSeO4] tetrahedra are the main contributors to its NLO properties. This study indicates that pure selenate is a promising material system to afford NCS structures with SHG responses.

This research was financially supported by the National Natural Science Foundation of China (no. 51432006), the Ministry of Education of China for the Changjiang Innovation Research Team (no. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (no. B13025), and the Innovation Program of Shanghai Municipal Education Commission. C.W. thanks the National and Shanghai Postdoctoral Program for Innovative Talents (nos. BX201800216 and 2018192). M.G.H. thanks the Australian Research Council for support (DP170100411).

The development of nonlinear optical (NLO) materials has been hindered by competing microstructure requirements: the need to simultaneously engineer a large hyperpolarizability (a large second-harmonic generation (SHG)) and a wide HOMO-LUMO gap (a wide band gap). Herein, a non-centrosymmetric transition-metal (TM) oxyfluoride K

Nonlinear optical (NLO) materials have critically important applications in advanced laser technologies. However, achieving a good balance between the mutual competing NLO properties and band gap w...

Electrical tuning of the nonlinear absorption of materials has promising application potential, while studies remain rare. In this work, we show that the third-order nonlinear absorption of poly(3,4-ethylenedioxythiophene) chemically doped with poly(styrene sulfonic acid) [PEDOT:PSS] can be effectively modulated by external voltage. The nonlinear absorption of the film can be varied between reverse saturable absorption (RSA) and saturable absorption (SA) via voltage control with laser excitation at 800 nm, and the corresponding nonlinear absorption coefficient can be tuned in the range -1606 ± 73 to 521 ± 9 cm GW-1. The doping level and energy structure of PEDOT are modulated with different voltages. The undoped film affords two-photon absorption and accordingly the RSA response. A moderately doped sample has two polaron levels, and Pauli blocking associated with these two polaron levels results in SA. The bipolaron level in heavily doped PEDOT leads to excited-state absorption and therefore RSA behavior. The approach reported here can be applied to other semiconductors and is a convenient, effective, and promising method for the electrical tuning of the optical nonlinearity.

One-pot synthesis of a new doubly boron-doped polycyclic aromatic hydrocarbon of 6,12-dimesityl-6,12-dihydro-6,12-diboradibenzo[def,mno]chrysene (MDBDBC) was reported. MDBDBC features a rigid planar electron-deficient core structure and demonstrates good chemical and thermal stabilities. A low-lying LUMO of -3.53 eV, a low locally excited triplet energy of 1.92 eV, as well as green electroluminescence with maximum EQE of 4.9% were found for MDBDBC, suggesting its potential as an n-type unit for future organic light emitting diode applications.

Oligo(p-phenyleneethynylene)s (OPEs) end-capped with (alkynyl)bis(diphosphine)ruthenium and thiol/thiolate groups stabilize ca. 2 nm diameter gold nanoparticles (AuNPs). The morphology, elemental composition and stability of the resultant organometallic OPE/AuNP hybrid materials have been defined using a combination of molecular- and nano-material chacterization techniques. The hybrids display long-term stability in solution (more than a month), good solubility in organic solvents, reversible ruthenium-centered oxidation, and transparency beyond 800 nm, and possess very strong nonlinear absorption activity at the first biological window, and unprecedented two-photon absorption activity in the second biological window (σ2 up to 38,000 GM at 1,050 nm).