Three-photon Absorption Cross-section Research Articles

A three-photon probe for highly selective and sensitive detection of Ag+ bearing an AIE fluorophore

It is well known that the silver ions (Ag+) are important in the human body, however, novel probes were lacked with good water solubility, biocompatibility and deep penetration to detect Ag+ in the organism. In this work, we report two new three-photon absorption AIE luminogens (AIEgen), abbreviated as Tpy and Tpy-Hex, whereby Tpy-Hex could detect intracellular and environmental Ag+ quantitatively at a micromolar level. Tpy-Hex binding with Ag+ possesses enhanced three-photon absorption cross-section under1550 nm excitation (NIR II window), which is indeed beneficial for deep penetration in vitro and in vivo. The mechanism underlying the changes in three photon absorption spectra caused by bromohexyl chain substitution was further explored. The fluorescence bioimaging results reveal that the proposed probe Tpy-Hex could be ultra-sensitive for detection of Ag+ in HeLa cells and poisoned mice.

Linear and nonlinear photophysical properties of ZnSe/CdS/ZnS core/shell/shell type II nanocrystals

In this work, one kind of type II ZnSe/CdS/ZnS core/shell/shell nanocrystals (NCs) is synthesized, and their linear and nonlinear photophysical properties are investigated. Through measurements of the temperature-dependent photoluminescence spectra of NCs, their excitonic properties, including the coefficient of the bandgap change, coupling strength of the exciton acoustic phonons, exciton longitudinal optical (LO) phonons, and LO–phonon energy are revealed. Femtosecond transient absorption spectroscopy was employed to obtain insight into ultrafast processes occurring at the interface of ZnSe and CdS, such as those involving the injection of photo-induced electrons into the CdS shell, interfacial state bleaching, and charge separation time. At the end, their multiphoton absorption spectra were determined by using the z-scan technique, which yielded a maximum two-photon absorption cross section of 3717 GM at 820 nm and three-photon absorption cross section up to 3.9 × 10 − 77 cm 6 · s 2 · photon − 2 at 1220 nm, respectively. The photophysical properties presented here may be important for exploiting their relevant applications in optoelectronic devices and deep-tissue bioimaging.

NIR-IIb excitable bright polymer dots with deep-red emission for in vivo through-skull three-photon fluorescence bioimaging

It is of great significance to study the brain structure and function in deep-tissue for neuroscience research and bio-medical applications because of the urgent demand for precise theranostics. Three-photon fluorescence microscopic (3PFM) bioimaging excited by the light in near-infrared IIb (NIR-IIb, 1,500–1,700 nm) spectral region is one of the most promising imaging techniques with the advantages of high spatial resolution, large imaging depth, and reduced scattering. Herein, a type of NIR-IIb light excitable deep-red emissive semiconducting polymer dots (P-dots) with bright 3PF and large three-photon absorption cross-section (σ3) at 1,550 nm was prepared. Then the P-dots were functionalized with polystyrene polymer polystyrene graft ethylene oxide functionalized with carboxyl groups (PS-PEG-COOH) and modified with NH2-poly(ethylene glycol) (PEG) to synthesis photochemically stable and biocompatible P-dots nanoparticles (NPs). Further the P-dots NPs were utilized for in vivo 3PFM bioimaging of cerebral vasculature with and without the brain skull under 1,550 nm femtosecond (fs) laser excitation. In vivo 3PFM bioimaging of the mice cerebral vasculature at various vertical depths was obtained. Moreover, a vivid three-dimensional structure of the mice vascular architecture beneath the skull was reconstructed. At the depth of 350 µm beneath the brain skull, 3.8 µm blood vessels could still be clearly recognized. NIR-IIb excitable P-dots assisted 3PFM bioimaging has great potential in accurate deep tissue bioimaging.

Facile Synthesis of Efficient Luminogens with AIE Features for Three-Photon Fluorescence Imaging of the Brain through the Intact Skull.

Visualization of the brain in its native environment is important for understanding common brain diseases. Herein, bright luminogens with remarkable aggregation-induced emission (AIE) characteristics and high quantum yields of up to 42.6% in the solid state are synthesized through facile reaction routes. The synthesized molecule, namely BTF, shows ultrabright far-red/near-infrared emission and can be fabricated into AIE dots by a simple nanoprecipitation procedure. Due to their high brightness, large Stokes shift, good biocompatibility, satisfactory photostability, and large three-photon absorption cross section, the AIE dots can be utilized as efficient fluorescent nanoprobes for in vivo brain vascular imaging through the intact skull by a three-photon fluorescence microscopy imaging technique. This is the first example of using AIE dots for the visualization of the cerebral stroke process through the intact skull of a mouse with high penetration depth and good image contrast. Such good results are anticipated to open up a new venue in the development of efficient emitters with strong nonlinear optical effects for noninvasive bioimaging of living brain.

Efficient multiphoton absorption of near-infrared emitting Cu-doped ZnInS/ZnS nanocrystals

Due to their unique optoelectronic properties, doped semiconductor nanocrystals (NCs) are promising fluorescent probes for deep-tissue bioimaging applications. However, studies on the photophysical properties of cadmium-free doped NCs are scarce. In this study, we synthesized and studied the photophysical properties of one type of cadmium-free doped NCs (Cu: ZnInS/ZnS NCs), which exhibit near infrared-I (NIR-I) emission at 730 nm and long emission lifetime up to 1.38 μs. Femtosecond transient absorption spectra revealed a strong exciton coupling effect between the Cu2+ ions and the ZnInS/ZnS host, with a fast energy transfer time of ≈100 ps. More importantly, Cu: ZnInS/ZnS NCs exhibit efficient volume-normalized two- and three-photon absorption cross-sections in NIR-I (800–900 nm) and NIR-III regions (1600–1990 nm), with maximum values up to 6.9 GM nm−3 at 800 nm and 1.1 × 10−80 cm6 s2 photon−2 nm−3 at 1600 nm, respectively. This study can shed light on the exploration of novel environmentally friendly doped NCs for deep-tissue bioimaging applications.

Comparison studies of excitonic properties and multiphoton absorption of near-infrared-I-emitting Cu-doped InP and InP/ZnSe nanocrystals.

Cu-doped InP (Cu:InP) and InP/ZnSe nanocrystals (NCs) with near-infrared-I (NIR-I) emission were prepared and characterized. Femtosecond transient absorption spectra revealed that the epitaxial growth of a ZnSe diffusion barrier onto the Cu:InP core can amplify its exciton-dopant coupling strength, with the energy transfer times of $\sim{220}\;{\rm ps}$∼220ps for Cu:InP NCs and $\sim{183}\;{\rm ps}$∼183ps for Cu:InP/ZnSe NCs. Importantly, the Cu:InP/ZnSe NCs exhibit much larger two- and three-photon absorption cross sections, reaching $\sim{10162}$∼10162 GM at 1030 nm and $\sim{1.06} \times {{10}^{ - 77}}\;{{\rm cm}^6}\,{{\rm s}^2}\,{{\rm photon}^{ - 2}}$∼1.06×10-77cm6s2photon-2 at 1600 nm, compared with Cu:InP NCs.

Experimental and quantum chemical studies of the structural enhancement of three-photon absorption in two symmetrical fluorene derivatives

Three-photon absorption (3PA) cross-section dependence on structure property for two highly conjugated molecules is reported. 3PA cross-sections of the molecules were measured through an optimized method. A 37-fold enhancement was obtained by coupling. The mechanism of this significant enhancement in 3PA cross-section was investigated by density functional theory (DFT) and configuration interaction singles (CIS) method with 6−311 G basis sets. The influence of molecular structure property on the 3PA cross-section is discussed micromechanically. The experimental and theoretical results demonstrate that the coupling effect by C9=C9′ double bond is the most definitive factor for the enhancement behavior.

Aggregation-induced emission luminogen for in vivo three-photon fluorescence lifetime microscopic imaging

Compared with visible light, near-infrared (NIR) light has deeper penetration in biological tissues. Three-photon fluorescence microscopy (3PFM) can effectively utilize the NIR excitation to obtain high-contrast images in the deep tissue. However, the weak three-photon fluorescence signals may be not well presented in the traditional fluorescence intensity imaging mode. Fluorescence lifetime of certain probes is insensitive to the intensity of the excitation laser. Moreover, fluorescence lifetime imaging microscopy (FLIM) can detect weak signals by utilizing time-correlated single photon counting (TCSPC) technique. Thus, it would be an improved strategy to combine the 3PFM imaging with the FLIM together. Herein, DCDPP-2TPA, a novel aggregation-induced emission luminogen (AIEgen), was adopted as the fluorescent probes. The three-photon absorption cross-section of the AIEgen, which has a deep-red fluorescence emission, was proved to be large. DCDPP-2TPA nanoparticles were synthesized, and the three-photon fluorescence lifetime of which was measured in water. Moreover, in vivo three-photon fluorescence lifetime microscopic imaging of a craniotomy mouse was conducted via a home-made optical system. High contrast cerebrovascular images of different vertical depths were obtained and the maximum depth was about 600 [Formula: see text]m. Even reaching the depth of 600 [Formula: see text]m, tiny capillary vessels as small as 1.9 [Formula: see text]m could still be distinguished. The three-photon fluorescence lifetimes of the capillaries in some representative images were in accord with that of DCDPP-2TPA nanoparticles in water. A vivid 3D reconstruction was further organized to present a wealth of lifetime information. In the future, the combination strategy of 3PFM and FLIM could be further applied in the brain functional imaging.

Probing Multiphoton Photophysics Using Two-Beam Action Spectroscopy.

Multiphoton absorption (MPA) is an enabling technology for many applications. However, due to the low probability of MPA processes, their accurate characterization remains a challenge. Here we introduce a new technique, two-beam constant emission intensity (2-BCEIn) spectroscopy, that offers substantial advantages over other existing methods that use the generation of optical emission for the characterization of absorptive nonlinearities. We use 2-BCEIn to study nonlinear absorption in solutions of crystal violet lactone (CVL) over a range of excitation wavelengths in which the dominant nonlinear absorption process transitions from two-photon absorption (750 nm) to three-photon absorption (830 nm). At an excitation wavelength of 800 nm, both two-photon absorption and three-photon absorption contribute substantially to the nonlinear fluorescence excitation (NFE) signal, although the dynamic range of the NFE data is not sufficient to quantify the contributions of each process. 2-BCEIn spectroscopy enables the direct measurement of the local exponent at each emission intensity. 2-BCEIn measurements made at several different emission intensities demonstrate unambiguously that the nonlinear excitation of CVL at 800 nm cannot be described solely as the sum of a two-photon process and a three-photon process. A kinetic model that includes intrapulse excited-state absorption reproduces the features of the 2-BCEIn measurements and enables the determination of the ratio of the three-photon absorption cross section to the two-photon absorption cross section. Such information cannot easily be extracted from conventional NFE measurements. These results demonstrate the power and versatility of two-beam action spectroscopies for elucidating the complex photophysics of multiphoton absorption processes.

Aggregation-Induced Emission Luminogen with Deep-Red Emission for Through-Skull Three-Photon Fluorescence Imaging of Mouse

Imaging the brain with high integrity is of great importance to neuroscience and related applications. X-ray computed tomography (CT) and magnetic resonance imaging (MRI) are two clinically used modalities for deep-penetration brain imaging. However, their spatial resolution is quite limited. Two-photon fluorescence microscopic (2PFM) imaging with its femtosecond (fs) excitation wavelength in the traditional near-infrared (NIR) region (700-1000 nm) is able to realize deep-tissue and high-resolution brain imaging. However, it requires craniotomy and cranial window or skull-thinning techniques due to photon scattering of the excitation light. Herein, based on a type of aggregation-induced emission luminogen (AIEgen) DCDPP-2TPA with a large three-photon absorption (3PA) cross section at 1550 nm and deep-red emission, we realized through-skull three-photon fluorescence microscopic (3PFM) imaging of mouse cerebral vasculature without craniotomy and skull-thinning. Reduced photon scattering of a 1550 nm fs excitation laser allowed it to effectively penetrate the skull and tightly focus onto DCDPP-2TPA nanoparticles (NPs) in the cerebral vasculature, generating bright three-photon fluorescence (3PF) signals. In vivo 3PF images of the cerebral vasculature at various vertical depths were obtained, and a vivid 3D reconstruction of the vascular architecture beneath the skull was built. As deep as 300 μm beneath the skull, small blood vessels of 2.4 μm could still be recognized.

Aspect ratio-related three-photon absorption and mechanism of α-FeOOH nanorods in the near-infrared

Tuning a semiconductor nanomaterial with large three-photon absorption (3PA) cross section in the near infrared and investigating the relationship between the nanostructure and nonlinear optical properties is a challenging topic, which is of significance in potential applications. Here, we report the aspect ratio-related 3PA response of α-FeOOH nanorods (NRs) in the near infrared. Large 3PA cross section at room temperature is achieved as high as ~10−77 cm6 s2 photon−2 when the distribution of photo-induced and intrinsic surface polarization charges of excitons to both ends of NRs is tuned through the aspect ratio, yielding total enhancement more than three times larger than that of NRs with 12.1 nm diameter.

Exceptionally large two- and three-photon absorption cross-sections by OPV organometalation.

Oligo(p-phenylenevinylene)s (OPVs) containing up to 8 PV units and end-functionalized by ruthenium alkynyl groups have been prepared and their nonlinear absorption properties assessed using the Z-scan technique and employing low repetition rate femtosecond pulses. Exceptionally large two-photon absorption (ca. 12 500 GM at 725 nm) and three-photon absorption cross sections (ca. 1.6 × 10(-76) cm(6) s(2) at 1100 nm) are found for the 8PV-containing example, highlighting the potential of an "organometalation" approach to NLO-efficient organic materials.

Determination of multiphoton absorption of silk fibroin using the Z-scan technique

The multiphoton absorption of silk fibroin at 810 nm was determined by open-aperture Z-scan. Three-photon absorption was confirmed at this wavelength and the three-photon cross section of silk fibroin was measured. Silk fibroin of varying molecular weight was tested and the cross section was found to increase exponentially with increasing molecular weight. The confirmation of a relatively large three-photon absorption cross section in silk will help lay the groundwork for future investigation of direct laser writing of three-dimensional structures within a silk matrix.

First principles studies on one-, two-, and three-photon absorption properties of a symmetric carbazole derivative both in gas phase and solution

One-, two-, and three-photon absorption spectra of a novel symmetric carbazole derivative have been calculated by applying density functional response theory, both in gas phase and in a selection of solvents with increasing polarity. The effect from surrounding solvents is described by the polarizable continuum model. The effect of the choice of geometry, as well as the exchange–correlation functional has been carefully analyzed. It is found that the Coulomb attenuation method variant of Becke’s three-parameter exchange and the Lee–Yang–Parr correlation functional (CAMB3LYP) can reproduce very well the experimental one-photon absorption lineshape. The dielectric solutions enhance both one- and multi-photon absorption properties. Possible explanations for the discrepancy between calculated and experimental three-photon absorption cross sections have been analyzed in details. The calculation suggests that the possible involvement of excite-state absorption in the experimental measurement cannot be ruled out.

Synthesis and efficient three-photon excited green fluorescence of pyridine–triphenylamine conjugated dyes

Pyridine-end-capped triphenylamine derivatives (Py2-TPA)n (n = 1,2,4) were synthesized using palladium-catalyzed Heck reaction and characterized by 1H NMR, 13C NMR, and HRMS-MALDI-TOF. Three-photon absorption and three-photon excited fluorescence properties of chromophores (Py2-TPA)n were studied using a femtosecond Ti:Sapphire laser system. These chromophores exhibit efficient three-photon excited green fluorescence peaking at 540–590 nm. The three-photon absorption cross-section of σ3 = 6.99 × 10−79 cm6 s2 photon−2 in the femtosecond regime has been obtained from (Py2-TPA)4. The ratio of 3PA cross-sections in CH2Cl2 solution σ3 (Py2-TPA)4:σ3 (Py2-TPA)2:σ3 (Py2-TPA)1 is 6.0:4.2:1. The ratio of conjugated π-electron numbers in (Py2-TPA)n is 4.4(n = 4):2.6(n = 2):1(n = 1). The increasing the push–pull units of (Py2-TPA)n and π-electron conjugation length or increasing the extent of charge transfer from the ends to the middle aryl core results in an increase of the 3PA cross-section. The results indicate that large aromatic conjugated chromophores (Py2-TPA)n containing pyridine–triphenylamine D–A pairs and a conjugated aryl core provide a new opportunity for 3PA-materials and three-photon fluorophores for practical application.

Investigation on three-photon-absorption fitting method and three-photon-absorption-induced optical stabilication effect of a fluorene derivative

Three-photon absorption coefficient obtained by current nonlinear transmittance method has large fitting error because of uneven laser radiation distribution. Relatively small three-photon absorption cross section values of present nonlinear molecules restrict their practical applications. In this paper, an accurate three-photon absorption coefficient fitting method is presented, which is applicable for a variety of laser distributions. A fluorene-based derivative, 2, 7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene, is synthesized. Apparent three-photon-absorption-induced optical stabilization effect is shown.

Impact of Electron Acceptor on Three-Photon Absorption Cross-Section of the Fluorene Derivatives

Small three-photon absorption (3PA) cross-section values of present nonlinear organic molecules limit their practical applications. Although electron donors and electron acceptors have a great effect on 3PA cross-section, little is known about how the strength and situation of electron acceptors influence the 3PA cross-section value of a compound. The present work reports 3PA effects of two fluorene derivatives with symmetric D-π-π(A)-π-D archetype, which are named as 2,7-bis(4-methoxyphenylacetylene)-9-fluorenone (FATT) and 2,7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene (TSATL). Large 3PA cross-section and ideal 3PA-induced optical limiting effects have been found in the two fluorene derivatives. The two molecules both have a different electron acceptor on the fluorene core, by which the 3PA cross-section value for FATT is enhanced by nearly 3-fold compared with that for TSATL. The mechanism of this significant enhancement in 3PA cross-section has been investigated by density functional theory (DFT) and configuration interaction singles (CIS) method with use of 6-311+G basis set in combination with conductor polarizable continuum model (CPCM). The theoretical results show that increase of electronegative character of the electron acceptor on the core is responsible for the increase of 3PA cross-section values of the two molecules.

Three-photon-absorption-induced optical stabilization effects in a bifluorenylidene derivative

A bifluorenylidene derivative with extended π-conjugated system has been designed and successfully synthesized. The compound displays strong three-photon absorption effect. The obtained three-photon absorption cross section is as high as 81.3 × 10(-76) cm(6)s(2). Distinguished 3PA-induced optical limiting and optical stabilization performances have been achieved. The on-axis transmitted intensity approached a constant even though the incident laser pulse fluctuation was 300%.

Three-photon absorption in a push–pull type chromophore containing tricyanofuran acceptor

Abstract Three-photon absorption (3PA) of a push–pull chromophore, 2-(3-cyano-(3-(4-(dimethylamino)styryl)-5, 5-dimethylcyclohex-2-enylidene)methyl)-5, 5-dimethylfuran-2-ylidene) malononitrile (CFM) including TCF group was measured by the nonlinear transmission method using a femto-second Ti:Sapphire oscillator-amplifier laser system. Its three-photon absorption cross-sections at 1300 nm were 36.8 × 10−79 cm6 s2 in the solution of DMF and 12.3 × 10−79 cm6 s2 in the solution of CH2Cl2, respectively. The large values were got by experiments in this paper, which is a new exploration for these kinds of materials. The molecule has the potential application foreground of 3PA areas and optical power limiting.

Exceptionally Strong Multiphoton-Excited Blue Photoluminescence and Lasing from Ladder-Type Oligo(p-phenylene)s

We report the synthesis and investigation of multiphoton absorption properties of a novel series of diphenylamino-end-capped ladder-type oligo(p-phenylene)s which exhibit greatly enhanced and efficient multiphoton (from two- to five-photon) upconverted blue photoluminescence with which the record-high intrinsic three-photon absorption cross-section of 4.56 × 10(-76) cm(6) s(2) in the femtosecond regime has been obtained. Exceptionally efficient two- to five-photon-excited lasing in the blue region has also been demonstrated in which the highest two-photon-excited lasing efficiency of 0.34% has been achieved.