Large Three-photon Absorption Cross Section Research Articles

Aggregation-induced emission nanoprobe assisted ultra-deep through-skull three-photon mouse brain imaging

Optical microscopy has enabled in vivo monitoring of brain structures and functions with high spatial resolution. However, the strong optical scattering in turbid brain tissue and skull impedes the observation of microvasculature and neuronal structures at a large depth. Herein, we proposed a strategy to overcome the influence induced by the high scattering effect of both skull and brain tissue via the combination of skull optical clearing (SOC) technique and three-photon fluorescence microscopy (3PM). The visible-NIR-II compatible skull optical clearing agents (VNSOCA) we applied reduced the skull scattering and water absorption in long wavelength by refractive index matching and H2O replacement to D2O respectively. 3PM with the excitation in the 1300-nm window reached 1.5 mm cerebrovascular imaging depth in cranial window assisted by a kind of bright aggregation-induced emission (AIE) nanoprobe we developed with a large three-photon absorption cross section. Combining the two advanced technologies together, we achieved so far the largest cerebrovascular imaging depth of 1.0 mm and neuronal imaging depth of> 700 µm through intact mouse skull. Dual-channel through-skull imaging of both brain vessels and neurons was also successfully realized, giving an opportunity of non-invasively monitoring the deep brain structures and functions at single-cell level simultaneously.

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.

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.

Quantum interference between multi photon absorption pathways in organic solid

We demonstrate spatial interference fringe pattern by simultaneous one- and three-photon absorption of UV and near-IR femtosecond pulses in thin film organic solid at room temperature. We use organic dendrimers that are specially designed to have strong fluorescence and very large three-photon absorption cross-section. High fringe visibility allows the quantum interference to be observed by eye.

Large three-photon absorption cross-section in a novel class of bis-( N-carbazolyl) fluorene derivatives

Two novel symmetrical charge transfer fluorene derivatives (abbreviated as BCZF and BVCZF) with carbazole end-group as the donor moieties have been synthesized. Three-photon absorption cross-sections of these two compounds have been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 140 × 10 −78 and 400 × 10 −78 cm 6 s 2 for BCZF and BVCZF, respectively. The geometries, electronic structures and electronic spectra of these two compounds are systematically studied by AM1 and ZINDO/S methods. On the basis of correct UV–vis spectra, the influence of different molecular structure on three-photon absorption cross-sections is discussed micromechanically.

Synthesis of New Symmetrically Substituted Stilbenes with Large Multi-Photon Absorption Cross Section and Strong Two-Photon-Induced Blue Fluorescence

Abstract Efficient Ti-catalyzed reductive coupling methodology was first employed to synthesize three new chromophores, whose chemical structures have been characterized by IR, 1H NMR, MS spectra, and elemental analyses. These dye solutions exhibit the linear transmission of ca. 90% at wavelengths ≥ 500 nm at the concentrations of 0.005–0.0005 mol dm−3. Pumped by ca. 700 nm laser irradiation, they possess large two-photon absorption cross sections of 44.5 × 40−48–62.0 × 10−48 cm4 s photon−1, and strong up-conversion blue fluorescence occuring at 437–452 nm. A large three-photon absorption cross section of 27.3 × 10−76 cm6 s2 photon−1 has also observed for one of these dyes under ca. 990 nm laser irradiation.

Synthesis and Characterization of a Novel Charge Transfer Compound with Large Three-Photon Absorption Cross Section

Abstract A new intramolecular charge transfer compound containing diethylamino group as electronic donor and oxadiazole group as electronic acceptor has been synthesized using Wittig–Horner reaction. This long conjugated molecule has large three-photon absorption cross section excited at 1.06 μm lasing.