Their Two-photon Absorption Research Articles

Predicting Two-Photon Absorption Spectra of Octupolar Molecules: A Deep-Learning Approach Based Exclusively on Molecular Structures.

Octupolar molecules possessing a strong two-photon response are vital for numerous advanced applications. However, accurately predicting their two-photon absorption (TPA) spectra requires high-precision quantum chemical calculations, which are computationally expensive due to repeated simulations of molecular excited-state properties. To address this challenge, we introduce a deep learning approach capable of rapidly and accurately forecasting TPA spectra for octupolar molecules. By leveraging the geometric structure as an initial descriptor, we employ a graph neural network to predict the maximum two-photon transition wavelength and cross-section. Our model demonstrates a mean absolute percentage error of less than 4% compared to time-dependent density-functional theory calculations, effectively reproducing experimental observations. Notably, this deep learning technique is nearly 100 000 times faster than comparable quantum calculations, making it an efficient and cost-effective tool for simulating TPA properties of octupolar molecules. Furthermore, this method holds great promise for the high-throughput screening of exceptional TPA materials.

Quaternary CsPbX3 (X = Cl1−xBrx, Br1−xIx) alloy microplates synthesized by single-step chemical vapor deposition and their two-photon absorption (TPA) properties

Because of their well-defined light–matter interaction volume, high-quality single-crystalline nature, and precise bandgap tunability, all-inorganic cesium lead halide (CsPbX3 (X = Cl, Br, I)) perovskite (IHP) microplates are of fundamental and technological interest today.

Synthesis, photophysical characterization, and integration of two-photon-responsive fluorophores in mesoporous organosilica nanoparticles for biological imaging use

We report the synthesis of new graftable three-branched octupolar fluorophores (F and F2), based on a triphenylamine core connected to electron-withdrawing sulfone-based peripheral groups through one or two π-conjugated phenylene-vinylene linkers. Their two-photon absorption (TPA), solvatochromism and photoluminescence properties were investigated to derive structure-property relationships. Notably, the chromophores presented TPA bands in the biological window (700–900 nm) and high TPA cross-sections at peak of 810 GM for F and F2. Then, after silylation, fluorophore F was further covalently integrated within the sol-gel synthesis of different periodic mesoporous organosilica nanoparticles (PMO NPs). Transmission electronic microscopy imaging revealed the formation of spherical NPs with good monodispersity in size, as confirmed by dynamic light scattering measurements. The obtained fluorophore-based nanoplatforms were shown to be biocompatible in vitro and demonstrated a good potential for two-photon imaging in cancer cells using two-photon excited fluorescence microscopy.

Spectrally Resolved Nonlinear Optical Properties of Doped Versus Undoped Quasi-2D Semiconductor Nanocrystals: Copper and Silver Doping Provokes Strong Nonlinearity in Colloidal CdSe Nanoplatelets

Nonlinear optical processes are crucial for emerging applications including multiphoton-excited fluorescence microscopy and optical power limiting. Therefore, searching for materials of high multiphoton absorption cross sections is essential for the development of these techniques. We present synthesis of 4.5 monolayer CdSe nanoplatelets (NPLs) doped with silver and copper ions along with the evaluation of their two-photon absorption (TPA) and three-photon absorption (3PA) cross sections. Doping significantly increases the TPA cross section of each NPL sample, which reaches up to 1.33 × 107 GM for the most absorbing copper-doped ones. We also detected 1–2 orders of magnitude-enhanced 3PA cross sections for the doped NPLs in comparison with their undoped counterparts. As TPA and 3PA peaks appear, in the first and the second biological transmission windows, respectively, doped NPLs are promising candidates for multiphoton fluorescence microscopy as bioimaging agents. Moreover, the strong nonlinear response suggests application as active optoelectronic materials in optical sensors.

Two‐Photon Absorption Properties in “Push‐Pull” Ruthenium Nitrosyl Complexes with various Fluorenylterpyridine‐Based Ligands

AbstractUsing the compound [RuII(FT)(bipy)(NO)](PF6)3 (FT is the electron‐rich 4’‐(2‐fluorenyl)‐2,2’:6’,2’’‐terpyridine ligand and bipy is 2–2’bipyridine) as a reference, two new compounds are presented in which carbon‐carbon double and triple bonds are inserted between the fluorenyl substituent and the terpyridine to provide an extended conjugation path. The electronic properties of the three complexes are compared experimentally by UV‐visible spectroscopy and computationally by means of the density functional theory. All of them exhibit a capability for NO release under irradiation on their low‐energy transition located in the 400–500 nm range, with a quantum yield around 0.01. Their two‐photon absorption (TPA) cross sections are investigated by the Z‐scan technique at λ=800 nm. While the reference compound exhibits a cross‐section equal to 108 GM, the introduction of double and triple bonds leads to increased cross‐sections equal to 131 GM and 150 GM, respectively. These values are discussed in reference to the two‐level model in use for “push‐pull” dipolar TPA chromophores.

Functional CdS-Au Nanocomposite for Efficient Photocatalytic, Photosensitizing, and Two-Photon Applications.

We demonstrate a low-temperature synthesis of hydrophilic, penicillamine-stabilized hybrid CdS-Au nanoparticles (NPs) utilizing different Au concentrations. The obtained hybrid nanomaterials exhibit photoluminescence quenching and emission lifetime reduction in comparison with their raw semiconductor CdS NPs counterparts. An increase of concentration of Au present at the surface of CdS leads to lower photoluminescence intensity and faster emission decays, suggesting more efficient charge separation when larger Au domains are present. For photocatalysis studies, we performed methylene blue (MB) absorption measurements under irradiation in the presence of CdS-Au NPs. After 1 h of light exposure, we observed the absorbance decrease to about 35% and 10% of the initial value for the CdS-5Au and CdS-7.5Au (the hybrid NPs obtained in a presence of 5.0 and 7.5 mM Au), respectively, which indicates MB reduction caused by electrons effectively separated from holes on metal surface. In further similar photocatalysis experiments, we measured bovine serum albumin (BSA) integrated photoluminescence intensity quenching in the presence of CdS-Au NPs, with a 50% decrease being obtained for CdS-2.5Au NPs and CdS-5Au NPs, with a faster response rate detected for the system prepared with a higher Au concentration. The results suggest hole-driven reactive oxygen species (ROS) production, causing BSA degeneration. Finally, we performed two-photon excited emission (TPEE) measurements for CdS-5Au NPs, obtaining their two-photon absorption (TPA) cross-section values up to 15.8 × 103 GM (Goeppert-Mayer units). We conclude that the obtained water-soluble CdS-Au NPs exhibit potential triple functionalities as photocatalysts for reduction and oxidation reactions as well as materials for two-photon absorption applications, so that they may be considered as future theranostics.

Replacing Two Chlorido Ligands by a Bipyridine Ligand in Ruthenium Nitrosyl Complexes with NO‐Release Capabilities: A Comparative Study

[RuII(FT)(bipy)(NO)][PF6]3 [FT is the electron‐rich 4′‐(2‐fluorenyl)‐2,2′:6′,2′′‐terpyridine ligand and bipy is 2,2′‐bipyridine] is synthesized and characterized. It crystallizes in the triclinic P1 space group [a = 9.5362(2) Å, b = 10.3946(4) Å, c = 22.5701(8) Å, α = 94.7400(10)°, β = 94.9400(10)°, γ = 101.0680(10)]. A photochemical study is presented in comparison with that of the parents cis(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6] and trans(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6]. The three derivatives release nitric oxide (·NO) under irradiation at λ = 405 nm with respective quantum yields of 0.06, 0.31, and 0.10. Their two‐photon absorption (TPA) cross‐sections (σTPA) were investigated by the Z‐scan technique on related derivatives in which two hexyl chains were introduced to improve their solubility while their spectroscopic properties remained almost unaffected. The resulting σTPA values of 100 GM at λ = 800 nm are in the window of transparency for human tissues, and the bipyridine‐based complex exhibits a slight tendency for higher efficiency. The replacement of the [RuII(Cl)2(NO)] core by [RuII(bipy)(NO)] provides a much simpler synthesis, and the TPA‐induced ·NO‐release capabilities are in the same range of magnitude. Therefore, it is envisioned that ·NO donors of greater complexity with several metal centers could be investigated in future.

A theoretical investigation on two latest two-photon pH fluorescent probes

Abstract Intracellular pH plays critical roles in cell, enzyme, and tissue activities, including proliferation and ion transport, and muscle contraction. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, investigations on two-photon fluorescent probes are very rare. In this work, we thoroughly study two latest two-photon pH fluorescent probes and design two excellent two-photon pH fluorescent probes. One-photon properties of these pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated by using the DALTON program. The calculated results indicate that the designed CAE-CN can serve as a proper Photoinduced Charge Transfer two-photon pH fluorescent probe and the designed AP1 can serve as a proper Photoinduced Electron Transfer two-photon pH fluorescent probe.

A Theoretical Investigation of Two Typical Two‐Photon pH Fluorescent Probes

Intracellular pH plays an important role in many cellular events, such as cell growth, endocytosis, cell adhesion and so on. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, studies about two-photon fluorescent probes are very rare. In this work, the geometrical structure, electronic structure and one-photon properties of a series of two-photon pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated using the method of ZINDO/sum-over-states method. Two types of two-photon pH fluorescent probes have been investigated by theoretical methods. The mechanisms of the Photoinduced Charge Transfer (PCT) probes and the Photoinduced Electron Transfer (PET) probes are verified specifically. Some designed strategies of good two-photon pH fluorescent probes are suggested on the basis of the investigated results of two mechanisms. For the PCT probes, substituting a stronger electron-donating group for the terminal methoxyl group is an advisable choice to increase the TPA cross section. For the PET probes, the TPA cross sections increase upon protonation.

A theoretical study on magnesium ion–selective two-photon fluorescent probe based on benzo [h] chromene derivatives

The geometrical structure, electronic structure, and one-photon absorption (OPA) properties of a series of magnesium ion (Mg2+)-selective fluorescent probes based on benzo [h] chromene derivatives have been theoretically studied by using density functional theory (DFT) method and Zerner’s intermediate neglect of differential overlap (ZINDO) methods. Their two-photon absorption (TPA) properties are also calculated by using the method of ZINDO/sum-over-states. Results show that all studied probe molecules exhibit large TPA cross-section (δmax) in response to Mg2+ in 700- to 1,200-nm range. Furthermore, the δmax can be greatly enhanced by introducing acceptor groups to the lateral side of benzo [h] chromene. And that probes with stronger acceptor group show larger δmax and result in 70-fold enhancing when coordinate with Mg2+. Significantly, probe molecules with good cell permeability were also studied by replacing the hydrogen group with acetoxymethyl ester, but δmax changed slightly. These results shed light into the design strategy of efficient TP fluorescent probes with large δmax and good cell permeability for Mg2+ sensing in living systems.

Theoretical study of one- and two-photon absorption properties of pyrene derivatives

The geometrical structure, electronic structure, one-photon absorption (OPA) properties of pyrene and its derivatives have been theoretically studied by using density functional theory (DFT) method and Zerner’s intermediate neglect of differential overlap (ZINDO) methods, and their two-photon absorption (TPA) properties are calculated by the ZINDO/sum-over-states method. The results show that introducing donor groups to pyrene molecule, increasing the number of donor groups, extending the conjugated length, or forming circular conjugated dimer can increase the oscillator strength (f) in the TPA process and ultimately result in extremely large TPA cross-sections and strong OPA around 400 nm of pyrene derivatives. All these results give us some basic principles to design pyrene derivatives with large TPA cross-sections. This shed light into the significance of the pyrene derivatives as promising fluorescent probes in biochemistry when they were linked to some special recognizing groups.

Synthesis and Photophysical Properties of Donor–Acceptor Dithienophospholes

AbstractThe synthesis and detailed photophysical studies of a series of 2,6‐asymmetrically functionalized dithieno[3,2‐b:2′,3′‐d]phospholes are reported. One‐photon spectroscopy revealed that the materials show similar significant Stokes shifts supporting very polar excited intramolecular charge‐transfer (ICT) states. Investigation of their two‐photon absorption (TPA) behavior indicated that the materials are also valuable TPA chromophores with reasonable cross‐sections between 285–385 GM in the biologically relevant wavelength range 800–1100 nm. Moreover, the nonlinear optical features of the phosphole derivatives reported herein were found to remain almost unaltered after modification of the phosphorus center, either by oxidation and/or complexation.

The aggregation effects on the two-photon absorption properties of para-nitroaniline polymers by hydrogen-bond interactions

This paper has theoretically designed a series of aggregate polymers on the basis of several para-nitroaniline monomers by hydrogen-bond interactions. At the level of time-dependent hybrid density functional theory, it has optimized their geometrical structures and studied their two-photon absorption (TPA) properties by using analytical response theory. The calculated results exhibit that the aggregation effects not only bring out the considerable red shift of the excited energies but also greatly enhance the TPA intensities of the aggregate polymers in comparison with the para-nitroaniline monomer. The aggregate configurations also have an important influence on the TPA abilities of the polymers; the trimer has the largest TPA cross section. The electron transitions between the molecular orbits involving the strong TPA excitations of the trimer are depicted to illuminate the relationship between the intermolecular charge transfer and the TPA property.

Synthesis, Structure, and Two-Photon Absorption Studies of a Phosphorus-Based Tris Hydrazone Ligand (S)P[N(Me)N═CH-C6H3-2-OH-4-N(CH2CH3)2]3 and Its Metal Complexes

A phosphorus-supported multidentate ligand (S)P[N(Me)N=CH-C(6)H(3)-2-OH-4-N(CH (2)CH(3))(2)](3) (1) has been used to prepare mononuclear complexes LM [M = Fe (2) Co (3)] and trinuclear complexes L(2)M(3) [M = Mn (4), Ni (5), Zn (6), Mg (7), Cd (8)]. In both 2 and 3 the ligand binds the metal ion in a facial coordination mode utilizing three imino nitrogen (3N) and three phenolic oxygen (3O) atoms. The molecular structures of L(2)Mn(3), L(2)Ni(3), L(2)Zn(3), L(2)Mg(3), and L(2)Cd(3) (4-8) are similar; two trihydrazone ligands are involved in coordination to hold the three metal ions in a linear fashion. Each of the trishydrazone ligands behaves as a trianionic hexadentate ligand providing three imino and three phenolic oxygen atoms for coordination to the metal ions. The coordination environment around the two terminal metal ions is similar (3N, 3O) while the central metal ion has a 6O coordination environment. Third-order non-linear optical properties of these compounds as measured by their two-photon absorption (TPA) cross section reveals that while 1 does not possess obvious TPA activity, complexes 2 (3213 GM) and 4 (3516 GM) possess a large TPA cross section at 770 nm.

The Synthesis and One‐ and Two‐Photon Optical Properties of Dipolar, Quadrupolar and Octupolar Donor–Acceptor Molecules Containing Dimesitylboryl Groups

Two series of related donor-acceptor conjugated dipolar, pseudo-quadrupolar (V-shaped) and octupolar molecular systems based on the p-dimesitylborylphenylethynylaniline core, namely, 4-(4-dimesitylborylphenylethynyl)-N,N-dimethylaniline, 4-[4-(4-dimesitylborylphenylethynyl)phenylethynyl]-N,N-dimethylaniline, 3,6-bis(4-dimesitylborylphenylethynyl)-N-n-butylcarbazole and tris[4-(4-dimesitylborylphenylethynyl)phenyl]amine, and on the E-p-dimesitylborylethenylaniline motif, namely, E-4-dimesitylborylethenyl-N,N-di(4-tolyl)aniline, 3,6-bis(E-dimesitylborylethenyl)-N-n-butylcarbazole and tris(E-4-dimesitylborylethenylphenyl)amine have been synthesised by palladium-catalyzed cross-coupling and hydroboration routes, respectively. Their absorption and emission maxima, fluorescence lifetimes and quantum yields have been obtained and their two-photon absorption (TPA) spectra and TPA cross-sections have been examined. Of these systems, the octupolar compound tris(E-4-dimesitylborylethenylphenyl)amine has been shown to exhibit the largest TPA cross-section among the two series of approximately 1000 GM at 740 nm. Its TPA performance is comparable to those of other triphenylamine-based octupoles of similar size. The combination of such large TPA cross-sections and high emission quantum yields, up to 0.94, make these systems attractive for applications involving two-photon excited fluorescence (TPEF).

One‐Pot Synthesis of Core‐Modified Rubyrin, Octaphyrin, and Dodecaphyrin: Characterization and Nonlinear Optical Properties

AbstractModified 26π rubyrin, 36π octaphyrin, and 54π dodecaphyrin systems have been synthesized in moderately good yields through acid‐catalyzed condensations of terthiophene diols and tripyrranes. The product distributions are decided both by the acid catalyst concentration and by the nature of the meso substituents. For example, a new isomer of [26]hexaphyrin(1.1.1.1.0.0) (rubyrin) was obtained with 0.3 equiv. of p‐toluenesulfonic acid, when the meso substituent was mesityl in at least one of the precursors. A change of the mesityl substituent for a p‐methoxy substituent in terthiophene diol resulted in the formation of a [3 + 3 + 3 + 3] condensation product – [54]dodecaphyrin(1.1.1.1.0.0.1.1.1.1.0.0) – in addition to the expected rubyrin. Furthermore, an increase in the acid concentration to 0.6 equiv. resulted in the formation of a new [36]octaphyrin(1.1.1.1.1.1.0.0), in addition to the rubyrin and dodecaphyrin. A single‐crystal X‐ray analysis of octaphyrin represents the first example of a planar conformation of an octaphyrin with six meso links. In rubyrin 19, one thiophene ring, opposite to the terthiophene subunit, is inverted, while in octaphyrin 30 one pyrrole ring and two thiophene rings are inverted. The various conformational possibilities tested for the unsubstituted dodecaphyrin 28, at semiempirical level, suggest that the most stable conformation is a figure‐eight. The final geometry optimization of figure‐eight dodecaphyrin was done at the B3LYP/6‐31G* level of DFT. Octaphyrins and dodecaphyrins bind trifluoroacetate anion effectively in their diprotonated forms, the binding constants (K) being 638 M–1 for dodecaphyrin 28, and 415 M–1 for octaphyrin 30. Electrochemical data reveal HOMO destabilization with increasing π electron conjugation, consistently with the large red shifts of the absorption bands. Preliminary studies on the use of these expanded porphyrins as third‐order NLO materials were followed by measurements of their two‐photon absorption (TPA) cross‐sections [σ(2)]. The σ(2) values increase upon going from the 26π rubyrins to the 54π dodecaphyrins, confirming our earlier observation that increases in π‐conjugated electrons increase the TPA values.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

New photochromic bisthienylethene derivatives containing carbazole

AbstractSome new photochromic bisthienylethene (BTE) derivatives containing carbazole were synthesized by Suzuki coupling method. All compounds were characterized by 1H NMR spectra, 13C NMR, mass spectra, etc. Their optical, photochromic, and electrochemical properties were described. Moreover, their two‐photon absorption (TPA) properties were investigated both in open and closed forms, finding observable distinction in the TPA of the ring‐open and ring‐closed forms. These compounds could be used as two‐photon switches and for the potential applications in three‐dimensional optical storage. Copyright © 2007 John Wiley & Sons, Ltd.

Enhanced Two-Photon Absorption and Ultrafast Dynamics of a New Multibranched Chromophore with a Dibenzothiophene Core

A series of novel compounds with dibenzothiophene core branched structures have been synthesized, and their two-photon absorption (TPA) properties were investigated. Two-photon fluorescence (TPF) and z-scan techniques were carried out, and a significant enhancement in the TPA cross section was observed for ST-G2, which possesses the largest generation number among the studied samples. By using different solvents, the largest nonlinear optical (NLO) response was observed in the most polar solvent. Ultrafast pump-probe experiments were performed to probe the excited state dynamics in the branched molecules, and the obtained results further confirmed the TPA enhancement mechanism. Time-resolved fluorescence (TRFL) and TRFL anisotropy measurements reveal that there is an ultrafast charge localization to the intramolecular charge transfer (ICT) state followed by relaxation with a lifetime longer than 1 ns.

Synthesis, Fluorescence, and Two‐Photon Absorption of a Series of Elongated Rodlike and Banana‐Shaped Quadrupolar Fluorophores: A Comprehensive Study of Structure–Property Relationships

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylene-vinylene or arylene-ethynylene building blocks, bearing different acceptor or donor end-groups. Their absorption and photoluminescence, as well as their two-photon-absorption (TPA) properties in the near infrared (NIR) region, were systematically investigated to derive structure-property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems, and planarization of the core (fluorene versus biphenyl) always leads to an increase in the TPA cross sections. In contrast, increasing the conjugation length as well as replacement of a phenylene moiety by a thienylene moiety in the conjugated rods did not necessarily lead to increased TPA responses. The present study also demonstrated that the topology of the conjugated rods can dramatically influence the TPA properties. This is of particular interest in terms of molecular engineering for specific applications, as both TPA properties and photoluminescence characteristics can be considerably affected. Thus, it becomes possible to optimize the transparency/TPA and fluorescence/TPA efficiency trade-offs for optical limiting in the red-NIR region (700-900 nm) and for two-photon-excited fluorescence (TPEF) microscopy applications, respectively.

Synthesis and Two-Photon Absorption Properties of 9,10-Bis(arylethynyl)anthracene Derivatives

A series of 9,10-bis(arylethynyl)anthracene derivatives (1−8) have been synthesized and their two-photon absorption (TPA) cross sections were measured by nanosecond fluorescence measurement and femtosecond Z-scan methods. The λmax values of these molecules are very similar and the values are near 800 nm. The /MW of the dipole increases with the conjugation length, whereas those for the quadrupoles decrease slightly with MW. Also, the /MW of the octupole is smaller than the dipole. In all cases, /MW of the quadrupoles are larger than the dipoles. Moreover, the results of the femtosecond Z-scan experiment indicate significant contribution by the excited-state absorption in . Noteworthy is the good agreement between the structure−TPA property relationships determined by both methods.