Two-photon Absorption Cross-section Values Research Articles

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

Near-infrared two-photon excited photoluminescence from Yb3+-doped CsPbClxBr3-x perovskite nanocrystals embedded into amphiphilic silica microspheres.

Nonlinear absorption of metal-halide perovskite nanocrystals (NCs) makes them an ideal candidate for applications which require multiphoton-excited photoluminescence. By doping perovskite NCs with lanthanides, their emission can be extended into the near-infrared (NIR) spectral region. We demonstrate how the combination of Yb3+ doping and bandgap engineering of cesium lead halide perovskite NCs performed by anion exchange (from Cl- to Br-) leads to efficient and tunable emitters that operate under two-photon excitation in the NIR spectral region. By optimizing the anion composition, Yb3+-doped CsPbClxBr3-x NCs exhibited high values of two-photon absorption cross-section reaching 2.3 × 105 GM, and displayed dual-band emission located both in the visible (407-493 nm) and NIR (985 nm). With a view of practical applications of bio-visualisation in the NIR spectral range, these NCs were embedded into silica microspheres which were further wrapped with amphiphilic polymer shells to ensure their water-compatibility. The resulting microspheres with embedded NCs could be easily dispersed in both toluene and water, while still exhibiting a dual-band emission in visible and NIR under both one- and two-photon excitation conditions.

Theoretical explore of bridge and donor engineering for novel naphthalimide based photosensitizers for two-photo photodynamic therapy

Naphthalimide derivatives are widely used in the development of clinical drugs and fluorescent probes because of their high light stability and low dark toxicity. Among these applications, as the photosensitizer (PS) used in the two-photon photodynamic therapy (TP-PDT) process is a new application condition of naphthalimide derivatives. Nevertheless, the development of such PSs is still hampered by their short triplet state lifetime and insufficient two-photon absorption (TPA) cross section. In order to explore the influence of different π-linkers on the efficient naphthalimide based PSs and solve the above problems, this paper characterizes the photophysical properties related to TP-PDT process of a series of naphthalimide based molecules using density functional theory (DFT) and time-dependent DFT (TD-DFT). The results reveal that compared to molecules without linkers and with phenyl as the linker, the compounds using thiophene as the π-linker have better planarity and optical properties, such as larger TPA cross section, lower energy gap of the singlet−triplet state, larger spin-orbit coupling value, and longer triplet state lifetime. Specifically, molecules 3s-ph, 2s-thio∼4s-thio have large TPA cross section value (1028–1384 GM, 8.3–11.2 times of molecule 1s) and triplet state lifetime (1337–11609 μs, 1.6–14.2 times of molecule 1s), making them effective for TP-PDT process. Furthermore, molecule 1s-thio acts as a promising PS candidate that can effectively undergo type I process and circumvent type II process. It is hoped that our theoretical research can provide some worthy ideas for the design and synthesis of effective naphthalimide based PSs in experiments.

Two-Photon Absorption Response of Functionalized BODIPY Dyes in Near-IR Region by Tuning Conjugation Length and Meso-Substituents.

BODIPY dyes substituted by phenol or -COOMe units at the meso-position (C8) with and without a distyryl group including a methoxy moiety at the -C3 and -C5 positions of the BODIPY have been synthesized to analyze the photophysical properties. To clarify the ground-state interaction, absorption and emission features were investigated in the THF environment. Extending the π-conjugation with the methoxy moiety at -C3 and -C5 positions of BODIPY leads to a spectral shifting of the absorption maxima toward red by 120 nm. In addition, attaching the -COOMe unit at the meso-position of the BODIPY structure increases nonradiative molecular relaxation as compared to compounds possessing phenol substituents at the same position. We have investigated the effect of phenol and a -COOMe group and π-extended conjugation length with a methoxy moiety on the properties of two-photon absorption (TPA) and electron transfer dynamics by performing open-aperture (OA) Z-scan and femtosecond transient absorption spectroscopy measurements, respectively. The synthesized BODIPY compounds with the distyryl group including the methoxy unit show TPA character due to the longer conjugation length and therefore intramolecular charge transfer ability. Based on the OA Z-scan experiments upon photoexcitation with 800 nm pulsed laser light, TPA cross-section values were obtained as 74 and 81 GM for the compounds possessing phenol and -COOMe units at the meso-position of BODIPY treated by distyryl group with methoxy moieties, respectively. Additionally, optical and electronic properties were calculated theoretically by using the DFT method.

Molecular Design of Highly Efficient Heavy-Atom-free NpImidazole Derivatives for Two-Photon Photodynamic Therapy and ClO- Detection.

Two-photon photodynamic therapy (TP-PDT), as a treatment technology with deep penetration and less damage, provides a broad prospect for cancer treatment. Nowadays, the development of TP-PDT suffers from the low two-photon absorption (TPA) intensity and short triplet state lifetime of photosensitizers (PSs) used in TP-PDT. Herein, we propose some novel modification strategies based on the thionated NpImidazole (the combination of naphthalimide and imidazole) derivatives to make efforts on those issues and obtain corresponding fluorescent probes for detecting ClO- and excellent PSs for TP-PDT. Density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to help us characterize the photophysical properties and TP-PDT process of the newly designed compounds. Our results show that the introduction of different electron-donating groups at the position 4 of NpImidazole can effectively improve their TPA and emission properties. Specifically, 3s with a N,N-dimethylamino group has a large triplet state lifetime (τ = 699 μs) and TPA cross section value (δTPA = 314 GM), which can effectively achieve TP-PDT; additionally, 4s (with electron-donating group 2-oxa-6-azaspiro[3.3]heptane in NpImidazole) effectively realizes the dual-function of a PS for TP-PDT (τ = 25,122 μs, δTPA = 351 GM) and a fluorescent probe for detecting ClO- (Φf = 29% of the product 4o). Moreover, an important problem is clarified from a microscopic perspective, that is, why the transition property of 3s and 4s (1π-π*) from S1 to S0 is different from that of 1s and 2s (1n-π*). It is hoped that our work can provides valuable theoretical clues for the design and synthesis of heavy-atom-free NpImidazole-based PSs and fluorescent probes for the detection of hypochlorite.

Ketocoumarin-Based Photoinitiators for High-Sensitivity Two-Photon Lithography

Ketocoumarins are attractive and distinct photosensitizers due to their high molar extinction coefficients, high intersystem crossing coefficients, and high photochemical stability. As a classic commercial ketocoumarin-based two-photon initiator, 7-diethylamino-3-thenoylcoumarin (DETC) was widely used in two-photon lithography. However, the large fluorescence quantum yield and low two-photon absorption cross section value greatly limit its application in high-throughput nanofabrication. In this work, a series of DETC derivatives were developed by extending the length of the alkyl chain and integrating different donor and acceptor groups. These ketocoumarin-based initiators, namely, compounds 1–7, were designed, synthesized, and unambiguously characterized. Compared with DETC, these compounds exhibit higher molar extinction coefficient, lower fluorescence quantum yield, higher two-photon absorption cross section, and improved sensitivity in two-photon lithography. Among these molecules, compound 7 with expanded π-electron systems and structures with enhanced intramolecular charge transfer exhibits the best sensitivity in two-photon lithography. With compound 7-based photoresist, many kinds of complex three-dimensional patterns can be fabricated using two-photon lithography at a writing speed of up to 60 mm s–1. The high two-photon initiation sensitivity makes these compounds promising candidates for commercialization and provides a new design concept for the development of new initiators.

One-Pot Synthesis of Pyreno[2,1-b]furan Molecules with Two-Photon Absorption Properties.

The development of large π-conjugated polycyclic heteroaromatic materials is of immense interest, both in the academic as well as the industrial community. Herein, we present the efficient one-pot synthesis of novel pyreno[2,1-b]furan molecules from a newly designed intermediate, which display intense green emission (505-516 nm) in solution and a large red shift emission (625-640 nm) in the solid state, because of strong π-π stacking. More interestingly, the compounds exhibit novel two-photon absorption (TPA) properties, and the TPA cross-section (δ) value was increased to 533 GM by regulating the electronic effects of the substituents of the pyreno[2,1-b]furan molecules. This study not only offers a facile strategy for constructing new pyrene-fused luminescence materials with two-photon absorption properties but also provides a new chemical intermediate that opens up a new pathway to advanced materials.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence.

The use of two-photon absorption (TPA) for such applications as microscopy, imaging, and photodynamic therapy (PDT) offers several advantages over the usual one-photon excitation. This creates a need for photosensitizers that exhibit both strong two-photon absorption and the highly efficient generation of reactive oxygen species (ROS), as well as, ideally, bright luminescence. This review focuses on different strategies utilized to improve the TPA properties of various multi-photon absorbing species that have the required photophysical properties. Along with well-known families of photosensitizers, including porphyrins, we also describe other promising organic and organometallic structures and more complex systems involving organic and inorganic nanoparticles. We concentrate on the published studies that provide two-photon absorption cross-section values and the singlet oxygen (or other ROS) and luminescence quantum yields, which are crucial for potential use within PDT and diagnostics. We hope that this review will aid in the design and modification of novel TPA photosensitizers, which can help in exploiting the features of nonlinear absorption processes.

Zn(II) complexes based on functional organic ligands: Two-photon activity, theoretical calculation and bioimaging

An organic ligand (3-[4-(diphenylamino)styryl] pyridine, L) was synthesized. By complexation of L with ZnBr2 and Zn(NCS)2 respectively in methanol and dichloromethane, two complexes ZnBr2L2 (dye1) and Zn(NCS)2L2 (dye2) were prepared. The two dyes exhibit good one- and two-photon fluorescence performance with high fluorescence quantum yields and large two-photon absorption cross section values. The mechanism of one-photon absorption and one-photon excited fluorescence based on computational results was obtained by TDDFT/CAM-B3LYP method. The results of living cell imaging experiments exhibit their compatibility in cytoplasm of HepG2 cells and show their potential in fluorescence microscopy bioimaging

Theoretical Study of a Two-Photon Fluorescent Probe Based on Nile Red Derivatives with Controllable Fluorescence Wavelength and Water Solubility.

Hypochloric acid (HOCl) plays a vital role in the natural defense system, but abnormal levels of it can cause cell damage, accelerated human aging, and various diseases. It is of great significance to develop new probes for detecting HOCl in biosystems nondestructively and noninvasively. The purpose of this work is to explore new chemical modification strategies of two-photon excitation fluorescence (TPEF) probes to improve the poor water solubility and low efficiency in imaging applications. Nil-OH-6 has a two-photon absorption cross-section value as high as 243 GM and attains a good quantum yield of 0.49. In addition, the modification of terminal groups with different azetidine-heterospirocycles or N,N-dialkyl fused amino groups to Nile Red can effectively improve the fluorescence efficiency as well as increase the solubility to some extent. This study provides some strategies to simultaneously improve the fluorescence performance and solubility of these two-photon probes and, hence, reliable guidance and a foundation for the subsequent synthesis of TPEF probes based on Nile Red.

Great enhancement of two photon absorption cross section value by intramolecular charge transfer in newly synthesized triphenylamine-BODIPY derivative

Novel borondipyrromethene (BODIPY) compound without a −8 (meso) substituent containing triphenylamine moieties via Suzuki-Miyaura coupling was designed and synthesized to enhance two photon absorption (TPA) property. The effect of π-expanded triphenylamine moieties and absence of meso substitution in BODIPY core on charge transfer dynamics as well as two photon absorption properties were investigated by utilizing ultrafast transient absorption spectroscopy measurements and open aperture (OA) Z-scan experiments in the environment of both in solution and host poly (methyl methacrylate) (PMMA) polymer film. The BODIPY compound with triphenylamine moieties has intramolecular charge transfer characteristics from electron donating moieties to BODIPY core due to its strong electron donating property and long conjugation length. The BODIPY compound with triphenylamine moieties demonstrates higher TPA cross section compared to reference compound based on the OA Z-scan experiments attributed to the strong coupling between the highest occupied molecular orbitals of BODIPY and 4-N,N-diphenylaminobiphenyl moieties. TPA cross section values were found to be 58 GM and 688 GM at 800 nm wavelength for reference BODIPY (BDP-1) and BODIPY-triphenylamine (BDP-2) compounds, respectively. BODIPY-triphenylamine compound has one of the greatest TPCS value among of the studied BODIPY compounds in the literature and may be a good candidate for photodynamic therapy and bio-imaging applications due to the free heavy atom nature.

New triazine bridged triads based on BODIPY-porphyrin systems: Extended absorption, efficient energy transfer and upconverted emission

Two novel triads connecting a BODIPY to ethylenediamine substituted porphyrins via triazine linker have been synthesized and characterized. One of the triads is a linear D-A structure with one BODIPY (D) and one porphyrin (A) bridged by the triazine linker and the other one is a branched A-D4 structure with the porphyrin core linked to four BODIPY units. The triads show extended absorption in the visible region with contributions from both porphyrin (Soret band centred at 410–430 nm) and BODIPY units (strong absorption at ≈ 502 nm) in good agreement with the expected molar ratio. Both triads exhibit linear and nonlinear optical properties featuring an efficient energy transfer from the BODIPY donor to the porphyrin acceptor. The nonlinear upconverted emission properties of the triads were studied by two-photon excitation in the Near-infrared (NIR, 710–930 nm). The maximum two-photon absorption cross-section values for the triads (40–70 GM) are larger than those typically reported in this wavelength range for porphyrins and BODIPY. Both the green emission of BODIPY (≈514 nm) and the red emission of porphyrins (650–750 nm) were observed under NIR excitation at 930 nm. The distinct features of triads, namely i) an extended absorption; ii) an efficient energy transfer and iii) the nonlinear upconverted emission featuring a large separation between the excitation and emission wavelengths could be beneficial for application in sensing and imaging procedures.

Novel yellow- to red-emitting fluorophores: Facile synthesis, aggregation-induced emission, two-photon absorption properties, and application in living cell imaging

Four novel yellow-to red-emitting fluorophores with a 1-(2-hydroxyethyl) pyridinium core and different electron-donating terminal moieties (N-methylcarbazole, N,N-dibutylbenzenamine, N-methylpyrrole, and 2-methylfuran) were designed and facilely synthesized via the one-step Knoevenagel condensation. All these compounds (HPs) were characterized by 1H NMR, 13C NMR, and HRMS. Their photophysical properties including linear absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited fluorescence, were systematically investigated in various solvents. And the density functional theory calculations were conducted to analyze the electronic structures of HPs. The two-photon absorption cross-sections (δ) values of HPs measured by the Z-scan technique were determined to be as large as 1354 (1HP-CZ), 4462 (2HP-BA), 836 (3HP-PR), and 2944 GM (4HP-FU) in DMSO. The two-photon action cross-sections (Φ × δ) values of 1HP-CZ and 2HP-BA in H2O measured by the two-photon induced fluorescence method were about 50 GM. 1HP-CZ, 3HP-PR, and 4HP-FU also exhibited good water solubility. Meanwhile, it was found that 2HP-BA exhibited notable aggregation-induced emission characteristic in DMSO/H2O mixture. The aggregate particle size distribution of 2HP-BA was measured by the dynamic light scattering method, and the aggregation characteristic of 2HP-BA was observed by the transmission electron microscopy. Besides, 2HP-BA also exhibited red emission. Then, HPs with relatively low cytotoxicity were used for one- and two-photon excited fluorescence imaging in living HepG2 cells. The results indicate that HPs are potential candidates in the bioimaging field due to their photophysical properties and biocompatibility.

Ultrafast photophysical and nonlinear optical properties of novel free base and axially substituted phosphorus (V) corroles

The progression in synthetic procedures over the last two decades gave admittance to a wide variety of corroles for suitable potential applications such as photovoltaics, photonics, and bio-imaging. In this communication, we present results from our investigations of ultrafast photophysical processes and third-order nonlinear optical properties of newly synthesized donor-acceptor based free-base [(C6F5)3] and phosphorus [P-(OH)2(C6F5)3] corroles. The global analysis of the femtosecond transient absorption data based on the compartmental model revealed the corresponding time constants of several photophysical processes such as (a) internal conversion (τIC) in the 260–280 fs range (b) vibrational relaxation (τVR) in the 2.5-5 ps range and (c) nonradiative relaxation times (τnr) in the 4.15–7.6 ns range and finally (d) triplet lifetimes in the range of 25–50 μs. The two-photon absorption (TPA) cross-section measurements were performed using the femtosecond, kHz pulse Z-Scan technique at 600 nm and 800 nm and the retrieved TPA cross-section values were in the range of ~102 GM. Degenerate four-wave mixing measurements illustrated a large third-order nonlinear optical susceptibility χ(3) with a magnitude of 6.9 × 10−14 esu and instantaneous (sub-picosecond) response, suggesting a pure electronic contribution to the nonlinearity of these corroles. The discoveries from this study may help further to extend the capability of corroles as NLO materials for photonic applications.

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.

Two-photon fluorescent Zn2+ probe for ratiometric imaging and biosensing of Zn2+ in living cells and larval zebrafish

As an essential transition-metal ion in organism, zinc ion (Zn2+) plays a significant role in cellular metabolism, apoptosis and neurotransmission. Herein, we reported a new intramolecular charge transfer-based two-photon probe, (E)-1-(6-(4-(2-(2-(2-methoxyethoxy)ethoxy)eth-oxy)-3,5-dimethylstyryl)quinolin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (TEO-MPVQ), for ratiometric imaging and biosensing of Zn2+ in living cells and larval zebrafish. The maximum two-photon absorption cross-section values (δmax) of the developed probe increased from 115 ± 16 GM to 188 ± 27 GM, after the probe was chelated with Zn2+. The emission spectrum of TEO-MPVQ probe increased and red-shifted about 60 nm, resulting in the ratiometric determination of Zn2+ with high sensitivity and selectivity. The present fluorescent probe also demonstrated good biocompatibility, high spatial resolution and deep penetration depth for Zn2+ detection. Accordingly, TEO-MPVQ was able to track the endogenous Zn2+ release in neurons and also successfully applied for larval zebrafish imaging. By using of this effective probe, it was found that the endogenous Zn2+ was rapidly released from metallothionein under the stimulation of NO in neurons.

DFT study of two-photon absorption of octupolar molecules

The two-photon absorption (TPA) properties of octupolar molecules based on a triphenyl-isocyanurate cyclotrimer, a 1,3,5-triphenyl-benzene or a triphenyl-triazine core were theoretically investigated using DFT and TD-DFT computations. These compounds are very promising regarding their potential application, especially for optical limitation. These systems, which exhibit a threefold axis, contain three arms with a terminal electron-donating group linked in 1, 3 and 5 positions to the central C3N3O3 isocyanurate, benzene or triazine ring. The SAOP functional and a DZP basis set were selected for the TPA computations. The so-computed TPA energies and cross sections are in good agreement with the observed data. Increasing the strength of the donor terminal group enhances the TPA cross section values. The compound with triazine core presents the highest two-photon cross section value compared to the values found for the isocyanurate or the 1,3,5-phenyl core as central ring. Furthermore, this study brings to light a cooperative enhancement of the TPA property between the three arms attached to the isocyanurate ring.

Crystal structures, one- and two-photon excited fluorescence of two complexes based on D-π-A structural 2,2-bipyridine derivative

By coordination of an electron donor-π-bridge-electron acceptor (D-π-A) optical functional organic ligand (L) with ZnBr2 and HgBr2, two fluorescent complexes ZnBr2L (1) and HgBr2L (2) were obtained. The structures of them were solved by single crystal X-ray diffraction analysis. Study of linear and nonlinear optical properties has shown that the complexes exhibit excellent one- and two-photon excited fluorescence and large two-photon absorption cross-section values. Dye 1 shows the potential application in fluorescence microscopy bioimaging.

Substituent effects on linear and nonlinear optical properties of fluorescent (E)-2-(4-halophenyl)-7-arlstyrylimidazo[1,2-A]pyridine: spectroscopic and computational methods

Abstract Effects of alkylamino and bromo substituents on imidazo[1,2-a]pyridines containing donor-π-acceptor type groups were comprehensively investigated for their linear and nonlinear optical properties by solvatochromic and DFT (CAM-B3LYP and BHandHLYP) methods. The difference between the ground and excited dipole moments as well as their ratios obtained by solvatochromic analysis indicate that the excited state is more polar than the ground state for both the bromo and diethyl amino derivative. More than twofold enhancement in the excited state dipole moments was observed as revealed by the difference and ratio of dipole moment upon the introduction of alkylamino donor group and these suggest large intramolecular charge transfer in the dyes. Stabilization energy above 20 kJ/mol was observed for large number of electron donor–acceptor interactions in Natural Bonding Orbital (NBO) analysis. Bond length alternation (BLA) and Bond order alternation (BOA) values tend to zero suggesting a high degree of polarization in the dyes. Enhancement in mean polarizability (α0), first hyperpolarizability (β0) and second static hyperpolarizabilities ( $\bar \gamma$) were observed by the introduction of alkylamino and bromo group in place of chloro in spite of the fact that Hammett constant of chloro and bromo are the same. The dyes have fundamental and intrinsic properties within the Hamiltonian limits. The two-photon absorption cross section value (≈100 GM) is comparable with LDS-698, a commercial TPA dye. This investigation is important for understanding the electronic structure of imidazo[1,2-a]pyridine with active functional groups and extending the potential for optical applications.

A series of two-photon absorption organotin (IV) cyano carboxylate derivatives for targeting nuclear and visualization of anticancer activities

Compared to organotin (IV) compounds with biochemical activity, two-photon absorption (2PA) organotin (IV) complexes for targeting nuclear with anticancer activities are rarely reported. Here, two novel 2PA organotin (IV) cyano carboxylate complexes (C1Sn-1, C1Sn-2) are synthesized and characterized. The two-photon absorption cross section values (δ) in the near-infrared region are significantly enhanced for C1Sn-2 compared to C1Sn-1, thus developing for targeting nuclear by two-photon fluorescence microscopy (2PFM). C1Sn-2 could specifically target nuclear DNA in vitro. The mechanism demonstrated that there are abundant hydrogen bond interactions between hydroxy group of C1Sn-2 and DNA. The animal mode studies are first proposed that C1Sn-2 displayed a certain anti-cancer efficiency with non-significant toxicity.