Multiphoton Absorption Properties Research Articles

Intraoperative tumor mapping using pyridine-carbazole based multifunctional fluorescent probes for precise resection and photodynamic therapeutics

Precise intraoperative tumor localization plays a pivotal role in the quest for refined cancer therapeutics. Addressing this, we have developed a series of novel pyridine-carbazole-based probes (Mito-Pyca1 ∼ Mito-Pyca4) featuring viscosity-enhanced fluorescence and multiphoton absorption properties. Among them, Mito-Pyca4 showcases significant promise for two-photon activated photodynamic therapy. When subjected to near-infrared irradiation, it reliably produces copious singlet oxygen, crucial for targeted tumor treatment. In vitro and in vivo experiments validated the capacity of Mito-Pyca4 to effectively induce cell apoptosis and impede tumor growth with minimal toxicity, positioning it as a potential candidate for photodynamic therapy. Furthermore, the specificity of Mito-Pyca4 for cancer cells was confirmed in co-culture experiments, and the probe was utilized for in vivo fluorescence-guided surgery. Successfully distinguishing tumor tissue from normal tissue, Mito-Pyca4 facilitates precise tumor resection. In summary, this comprehensive study establishes Mito-Pyca4 as a versatile tool for nonlinear optical imaging, viscosity sensing, and fluorescence-guided cancer surgery and treatment, providing surgeons an unparalleled advantage in discerning tumor margins. Through this research, we underscore the transformative potential of integrating chemical innovation with surgical and therapeutic techniques.

Multiphoton absorption properties and bioimaging of solvent coligand cyclometalated Pt(II) complex

As a cyclometalated complex, solvent coligand Pt(II) complex with multiphoton absorption has been designed and synthesized. After the optical properties of the Pt(II) complex were studied carefully, time-dependent density functional theory calculation (TD-DFT) was used to further identify the triplet charge transitions of the complex. The specific energy levels of frontier molecular orbitals and the data related to the energy level transition showed that the Pt(II) complex had photoluminescent properties, and their phosphorescence emission originated from 3LLCT/3MLCT. Because of nonlinear optics (NLO) response, the Pt(II) complex could act as multiphoton absorption materials for bioimaging and anticancer application.

Aggregation-induced emission cyclometallated Iridium(III) complex for multi-photon FLIM imaging-guided photodynamic therapy

Cyclometallated iridium(III) complexes have unique photophysical properties that turn them into promising photosensitizers and potential fluorescence lifetime imaging probes. Herein, we developed a novel cyclometallated iridium(III) complex (Ir–OH) with aggregation-induced emission (AIE) properties for FLIM imaging-guided photodynamic therapy. Studies on photophysical properties show that Ir–OH exhibits excellent fluorescence response to in situ mitochondrial viscosity with varied lifetime. In addition, Ir–OH shows satisfactory multiphoton absorption properties in the near-infrared region (Two-photon: 700–800 nm; Three-photon: 1150–1450 nm). More importantly, changes in mitochondrial viscosity during photodynamic processes can be quantified in real-time by FLIM. Thus, our work illustrates that cyclometallated iridium(III) complexes can simultaneously induce and precisely detect microenvironmental changes at the subcellular level using FLIM, leading to self-reporting PDT outcomes.

Novel metallated imidazole phthalocyanines: synthesis, ultrafast excited-state carrier dynamics and multiphoton absorption properties

Herein we report a comprehensive investigation of ultrafast photophysics and nonlinear optical properties of novel metallated imidazole phthalocyanines.

Multiphoton characterization and live cell imaging using fluorescent adenine analogue 2CNqA.

Fluorescent nucleobase analogues (FBAs) are established tools for studying oligonucleotide structure, dynamics and interactions, and have recently also emerged as an attractive option for labeling RNA-based therapeutics. A recognized drawback of FBAs, however, is that they typically require excitation in the UV region, which for imaging in biological samples may have disadvantages related to phototoxicity, tissue penetration, and out-of-focus photobleaching. Multiphoton excitation has the potential to alleviate these issues and therefore, in this work, we characterize the multiphoton absorption properties and detectability of the highly fluorescent quadracyclic adenine analogue 2CNqA as a ribonucleotide monomer as well as incorporated, at one or two positions, into a 16mer antisense oligonucleotide (ASO). We found that 2CNqA has a two-photon absorption cross section that, among FBAs, is exceptionally high, with values of σ2PA(700 nm) = 5.8 GM, 6.8 GM, and 13 GM for the monomer, single-, and double-labelled oligonucleotide, respectively. Using fluorescence correlation spectroscopy, we show that the 2CNqA has a high 2P brightness as the monomer and when incorporated into the ASO, comparing favorably to other FBAs. We furthermore demonstrate the usefulness of the 2P imaging mode for improving detectability of 2CNqA-labelled ASOs in live cells.

A cyclometallated iridium(III) complex with multi-photon absorption properties as an imaging-guided photosensitizer.

Conventional photosensitizers (PSs) often have shorter excitation wavelengths and poor cancer cell targeting, resulting in a limited tissue penetration depth and increased biotoxicity, which are significant barriers to ensuring effective photodynamic therapy (PDT) in vivo. In this work, a cyclometallated iridium(III) complex (Ir-Biotin) with a long excitation wavelength and effective cancer cell targeting was designed and synthesized. The initial in vitro assessment indicated that Ir-Biotin shows excellent PDT activity with a high singlet-oxygen (1O2) generation yield (0.19) due to the facilitated intersystem crossing process. Further study shows that Ir-Biotin shows good biocompatibility, has specific selectivity for cancer cells, and can induce apoptosis under laser irradiation. Furthermore, Ir-Biotin can be applied for imaging-guided PDT using an in vivo imaging system, and showed significant anti-tumour effects (tumour growth inhibition value: 87.66%). These results reveal the importance of long excitation wavelengths of photosensitizers for efficient PDT and suggest a promising strategy for developing effective photosensitizers.

Optical Properties and Applications of Crystalline Materials

Optical Properties and Applications of Crystalline Materials

Optical Kerr nonlinearity and multiphoton absorption of DSTMS measured by the Z-scan method

We investigate the optical Kerr nonlinearity and multiphoton absorption (MPA) properties of 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium 2, 4, 6-trimethylbenzene-sulfonate (DSTMS) excited by femtosecond pulses at a wavelength of 1.43 µm, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 µm are strongly anisotropic, indicating a dominating contribution from cascaded second-order nonlinearity.

Multi-photon absorption properties of semiconducting nanomaterials

Multiphoton absorption (MPA) is a nonlinear optical process that involves simultaneous absorption of two or more photons by a material to promote its ground state to an excited state. Multiphoton absorption promises many important applications such as multi-dimensional fluorescence imaging, three dimensional (3D) data storage. Physical and chemical properties of nanometer sized semiconductor materials change drastically due to quantum size effect. Combination of both multiphoton absorption and quantum effects will be an interesting study. Multiphoton absorption of semiconducting nanomaterials is an exciting phenomenon which promotes many important applications. This paper reviews multi-photon absorption properties of different kinds of semiconducting nanomaterials starting from chalcogenide-based nanomaterials to perovskites nanomaterials and their applications in various fields.

Enhanced optical power limiting and visible luminescence in colloidal dispersion of ultra-small Au nanoclusters synthesized by single-pot chemical technique

Here, we present a detailed investigation on the synthesis and nonlinear multiphoton absorption properties of the colloidal solution of Au nanoclusters (AuNCs) which contains the atomic clusters, with the number of atoms per cluster (NAC) of only one (Au1NC) and two (Au2NC). These AuNCs are synthesized by an easy single step one-pot simple chemical process and by using dimethylformamide (DMF) both as reducer and stabilizer. The presence of both Au1NC and Au2NC are found in the sample by their distinct signature in the UV–Vis. absorption spectrum as well as in the high-resolution mass spectrum. The synthesized material has been found to exhibits a strong and stable blue-luminescence with a moderately high quantum yield (QY) of 12.4% when excited with UV light. The nonlinear optical two-photon absorption (2PA) properties of Au1, Au2NC solutions are being reported here by Z-scan studies, for the first time, by using both 10 ns and 100 fs pulse laser radiations having wavelength of 532 nm. It is significantly noted here that the synthesized AuNCs are found to exhibit reverse saturable absorption (RSA) when excited either by ns or by fs laser pulses. A high third-order nonlinear susceptibility (ꭓ(3)) of the order of 10−13 (esu) of the synthesized materials are obtained under fs laser excitation and it is attributed to the 2PA through electronic band to band transition. In contrast, the variation of the 2PA coefficient (β) with input intensity (I0) represents the footprint of free carrier involvement in the enhanced nonlinear absorption in the case of ns excitation. Furthermore, through the non-saturable nonlinear multiphoton absorption, the synthesized AuNCs exhibit excellent optical power limiting phenomenon with the limiting threshold (Fth) of 9.1 mJ/cm2 (fs excitation) and 2.02 J/cm2 (ns excitation) owing to their enhanced 2PA coefficient. Therefore, we believe that our synthesized ultra-small colloidal AuNCs can be used as the promising candidate material for advanced photonics application in the future.

A generalized few-state model for the first hyperpolarizability.

The properties of molecules depend on their chemical structure, and thus, structure-property relations help design molecules with desired properties. Few-state models are often used to interpret experimental observations of non-linear optical properties. Not only the magnitude but also the relative orientation of the transition dipole moment vectors is needed for few-state models of the non-linear optical properties. The effect of the relative orientation of the transition dipole moment vectors is called dipole alignment, and this effect has previously been studied for multiphoton absorption properties. However, so far, no such studies are reported for the first hyperpolarizability. Here, we present a generalized few-state model for the static and dynamic first hyperpolarizability β, accounting for the effect of dipole alignment. The formulas derived in this work are general in the sense that they can be used for any few-state model, i.e., a two-state model, a three-state model, or, in general, an n-state model. Based on the formulas, we formulate minimization and maximization criteria for the alignment of transition dipole moment vectors. We demonstrate the importance of dipole alignment by applying the formulas to the static first hyperpolarizability of ortho-, meta-, and para-nitroaniline. The formulas and the analysis provide new ways to understand the structure-property relationship for β and can hence be used to fine-tune the magnitude of β in a molecule.

Two-Photon Absorption Cross-Sections in Fluorescent Proteins Containing Non-canonical Chromophores Using Polarizable QM/MM.

Multi-photon absorption properties, particularly two-photon absorption (2PA), of fluorescent proteins (FPs) have made them attractive tools in deep-tissue clinical imaging. Although the diversity of photophysical properties for FPs is wide, there are some caveats predominant among the existing FP variants that need to be overcome, such as low quantum yields and small 2PA cross-sections. From a computational perspective, Salem et al. (2016) suggested the inclusion of non-canonical amino acids in the chromophore of the red fluorescent protein DsRed, through the replacement of the tyrosine amino acid. The 2PA properties of these new non-canonical chromophores (nCCs) were determined in vacuum, i.e., without taking into account the protein environment. However, in the computation of response properties, such as 2PA cross-sections, the environment plays an important role. To account for environment and protein–chromophore coupling effects, quantum mechanical/molecular mechanical (QM/MM) schemes can be useful. In this work, the polarizable embedding (PE) model is employed along with time-dependent density functional theory to describe the 2PA properties of a selected set of chromophores made from non-canonical amino acids as they are embedded in the DsRed protein matrix. The objective is to provide insights to determine whether or not the nCCs could be developed and, thus, generate a new class of FPs. Results from this investigation show that within the DsRed environment, the nCC 2PA cross-sections are diminished relative to their values in vacuum. However, further studies toward understanding the 2PA limit of these nCCs using different protein environments are needed.

Spectral Dynamics and Multiphoton Absorption Properties of All-Inorganic Perovskite Nanorods.

All-inorganic perovskite (CsPbX3, X = Cl, Br, I) nanorods (NRs) not only retain their inherent advantages such as a high photoluminescence quantum yield and broad wavelength tunability but also exhibit superior photophysical properties including their extremely strong multiphoton absorption (MPA). However, the spectral dynamics and MPA properties of CsPbX3 NRs have not been fully investigated. Here, we report comprehensive comparison studies on the femtosecond spectral dynamical properties of CsPb(Br0.8Cl0.2)3, CsPbBr3, and CsPb(Br0.85I0.15)3 NRs, including their influences on their hot-carrier cooling, biexciton lifetime, and biexciton binding energy. Interestingly, although the three kinds of perovskite NRs have similar diameters and lengths, they differ significantly in their nonlinear optical properties, among which the CsPb(Br0.85I0.15)3 displayed the greatest MPA cross sections. Furthermore, the multiphoton-excited stimulated emission of CsPb(Br0.8Cl0.2)3 and CsPbBr3 NRs is demonstrated. This work indicates that CsPbX3 (X = Cl, Br, I) NRs are excellent candidates for exploring their applications in different optoelectronic devices.

Multiphoton absorption in low-dimensional cesium copper iodide single crystals

Two kinds of all-inorganic lead-free cesium copper iodide (CsCu2I3 and Cs3Cu2I5) single crystals (SCs) are synthesized and their multiphoton absorption (MPA) properties are comparatively investigated for the first time.

Deciphering the Ultrafast Nonlinear Optical Properties and Dynamics of Pristine and Ni-Doped CsPbBr3 Colloidal Two-Dimensional Nanocrystals.

While the unabated race persists in achieving record efficiencies in solar cells and other photonic/optoelectronic devices using lead halide perovskite absorbers, a comprehensive picture of the correlated third-order nonlinear optical (NLO) properties is yet to be established. The present study is aimed at deciphering the role of dopants in multiphoton absorption properties of intentionally engineered CsPbBr3 colloidal nanocrystals (NCs). The charge separation of the plasmon-semiconductor conduction band owing to the hot electron transfer at the interface was demystified using the dynamics of the bleached spectral data from femtosecond (fs) transient absorption spectroscopy with broadband capabilities. The NLO properties studied through the fs Z-scan technique revealed that Ni-doped CsPbBr3 NCs exhibited strong third-order NLO susceptibility of ∼10-10 esu. The exotic photophysical phenomena in these pristine and Ni-doped CsPbBr3 colloidal two-dimensional (2D) NCs reported herein are believed to provide the avenues to address the critical variables involved in the structural differences and their correlated optoelectronic properties.

Multi-photon properties in various condensed phases of dendritic chromophores derived from carbazole and indenoquioxaline units: Synthesis and characterization

We have used functionalized carbazoles and indenoquonoxalines as the main building units and enthynyl groups as the π-linkages to construct two novel dendritic fluorophores and studied their degenerate multi-photon absorption properties in both the solution phase and the neat-film state within femtosecond and nanosecond regions. In our experiments, these model compounds are found to manifest strong and widely dispersed two-photon absorption as well as effective power-limiting properties against ultra-short laser pulses in the near-IR region. In addition, both chromophores exhibit medium to strong three-photon-induced fluorescence, indicating such scaffold may serve as a reference structural motif for the development of three-photon materials.

Nonlinear optical and multi-photon absorption properties in graphene–ZnO nanocomposites

Graphene–ZnO (GZO) nanocomposites were synthesized by a modified solvothermal method, and characterized by transmission electron microscopy, x-ray diffraction, Raman spectra, and UV–vis absorption spectra. The controllable nonlinear optical (NLO) properties of as-prepared GZO nanocomposites were tested by an open-aperture Z-scan method with 1030 nm fs laser pulses; the tested results showed that there were five-photon absorption (5PA) at 46.8 GW cm−2, 3PA at 28.1 GW cm−2, 2PA at 18.7 GW cm−2, and a vital change from saturable absorption (SA) to reverse SA (RSA) with the increase of incident intensity. This was the first time that 5PA was found in GZO nanocomposites at such a low intensity, 46.8 GW cm−2. The tunable NLO property from SA to RSA and controllable multi-photon absorption provided a facile approach for their applications in optical, optoelectronic devices, and information storage.

Highly Efficient Multiphoton-Pumped Frequency-Upconversion Stimulated Blue Emission with Ultralow Threshold from Highly Extended Ladder-Type Oligo(p-phenylene)s.

A series of highly extended π-conjugated ladder-type oligo(p-phenylene)s containing up to 10 phenyl rings with (L)-Ph(n)-NPh (n=7-10) or without diphenylamino endcaps (L)-Ph(n) (n=7 and 8) were synthesized and investigated for their multiphoton absorption properties for frequency upconverted blue ASE/lasing. Extremely large two-photon absorption (2PA) cross-sections and highly efficient 2PA ASE/lasing with ultralow threshold were achieved. (L)-Ph(10)-NPh exhibits the highest intrinsic 2PA cross-section of 3643 GM for a blue emissive organic fluorophore reported so far. The record-high 2PA pumped ASE/lasing efficiency of 2.06 % was obtained by un-endcapped oligomer, (L)-Ph(8) rather than that with larger σ2 , suggesting that a molecule with larger σ2 is not guaranteed to exhibit higher η2 . All of these oligomers exhibit exceptionally ultralow 2PA pumped ASE/lasing thresholds, among which the lowest 2PA pumped threshold of circa 0.26 μJ was achieved by (L)-Ph(10)-NPh.

Highly Efficient Multiphoton‐Pumped Frequency‐Upconversion Stimulated Blue Emission with Ultralow Threshold from Highly Extended Ladder‐Type Oligo(p‐phenylene)s

AbstractA series of highly extended π‐conjugated ladder‐type oligo(p‐phenylene)s containing up to 10 phenyl rings with (L)‐Ph(n)‐NPh (n=7–10) or without diphenylamino endcaps (L)‐Ph(n) (n=7 and 8) were synthesized and investigated for their multiphoton absorption properties for frequency upconverted blue ASE/lasing. Extremely large two‐photon absorption (2PA) cross‐sections and highly efficient 2PA ASE/lasing with ultralow threshold were achieved. (L)‐Ph(10)‐NPh exhibits the highest intrinsic 2PA cross‐section of 3643 GM for a blue emissive organic fluorophore reported so far. The record‐high 2PA pumped ASE/lasing efficiency of 2.06 % was obtained by un‐endcapped oligomer, (L)‐Ph(8) rather than that with larger σ2, suggesting that a molecule with larger σ2 is not guaranteed to exhibit higher η2. All of these oligomers exhibit exceptionally ultralow 2PA pumped ASE/lasing thresholds, among which the lowest 2PA pumped threshold of circa 0.26 μJ was achieved by (L)‐Ph(10)‐NPh.

Synthesis and multi-photon absorption properties of symmetric bisarylacetylene chromophores using functionalized isomeric pyrazinoindenocarbazole units as the rigid aryl substituents

A pair of isomeric chromophores based on the skeleton of bisarylacetylene using functionalized pyrazinoindenocarbazole moieties as the aryl substituents has been synthesized and characterized for their two- and three-photon-related properties in the femtosecond and nanosecond regimes. Our experiments have found that both model fluorophores manifest strong two-photon absorption in the near infrared region with one of the isomers exhibiting superior maximum two-photon absorptivity. It is realized that both the isomeric forms of functionalized pyrazinoindenocarbazoles are useful π-units for the construction of highly two-photon active materials but the effectiveness of the units is unequal, which is probably attributed to the difference of their conjugated structures. Two-photon-based optical power-limiting and stabilization against nanosecond laser pulses of one isomer was demonstrated. Additionally, these two chromophores exhibit strong three-photon-induced fluorescence when excited by the nanosecond laser with longer wavelengths (≥1000 nm), implying their potential utility to serve as prototypes for the development of three-photon materials.