One-photon Fluorescence Research Articles

New ESIPT-Inspired Photostabilizers of Two-Photon Absorption Coumarin–Benzotriazole Dyads: From Experiments to Molecular Modeling

In this work, a variety of new coumarin–benzotriazole dyads are synthesized to study the photostabilities under the irradiation of broad UV light as well as near-infrared (near-IR) laser respectively inspired by efficient excited state intramolecular proton transfer (ESIPT). The corresponding esterified dyads and the coumarin dyes are prepared as the references. The intramolecular hydrogen bond in the target dyads is confirmed by 1H NMR spectra and UV/visible absorption spectra. The internal proton transfer in the excited states of the target dyads under single photon excitation and near-IR laser irradiation is demonstrated by the measurements of one-photon fluorescence spectra and two-photon upconverted fluorescence spectra, respectively. The photostabilities of the target dyads under broad UV light irradiation and near-IR laser irradiation in various organic solvents with saturated air, oxygen, or argon are studied. The theoretical evidence of ESIPT of the target dyads is provided by the molecular geome...

Self-Assembly of Electron Donor-Acceptor-Based Carbazole Derivatives: Novel Fluorescent Organic Nanoprobes for Both One- and Two-Photon Cellular Imaging.

In this study, we report fluorescent organic nanoprobes with intense blue, green, and orange-red emissions prepared by self-assembling three carbazole derivatives into nanorods/nanoparticles. The three compounds consist of two or four electron-donating carbazole groups linked to a central dicyanobenzene electron acceptor. Steric hindrance from the carbazole groups leads to noncoplanar 3D molecular structures favorable to fluorescence in the solid state, while the donor-acceptor structures endow the molecules with good two-photon excited emission properties. The fluorescent organic nanoprobes exhibit good water dispersibility, low cytotoxicity, superior resistance against photodegradation and photobleaching. Both one- and two-photon fluorescent imaging were shown in the A549 cell line. Two-photon fluorescence imaging with the fluorescent probes was demonstrated to be more effective in visualizing and distinguishing cellular details compared to conventional one-photon fluorescence imaging.

Two novel dyes containing spirobifluorene and triphenylamine: Synthesis, one- and two-photon excited fluorescence and applications as probes for silver ions, water and cell imaging

Two fluorophores, SPF-TNS and SPF-TBB, with electron-rich triphenylamine groups and Ag+ receptor units on the respective biphenyl branches of 9,9′-spirobifluorene were synthesized. They exhibit strong one- and two-photon excited fluorescence, and the two-photon absorption cross-section values are 665 GM for SPF-TNS and 355GM for SPF-TBB. The probing behaviors toward metal ions were investigated via UV/Vis absorption spectra as well as one-photon fluorescence changes. The results indicated that SPF-TNS and SPF-TBB exhibit distinct fluorescent quenching in the presence of silver ions that can be used for highly sensitive and selective naked-eye detection of Ag+. The one-photon excited fluorescence of SPF-TBB can be made to measure water content of organic solvents. The detection limits were calculated to be 0.04% for THF and 0.03% for 1,4-dioxane. The two-photon scanning microscopy experiments suggest that SPF-TNS is a promising label potentially applicable for the tracking of biomolecules.

A series of novel dibenzothiophene-based two-photon fluorescent probes for cellular nucleus imaging

In this study, a series of novel dibenzothiophene-based two-photon excited fluorescence (TPEF) probes with excellent nuclear staining ability were prepared and investigated. The one-photon photophysical properties indicated these labels possessed UV absorption wavelength of 390–393nm and quantum yields of 0.425–0.71. The two-photon photophysical performance exhibited two-photon absorption (TPA) cross-sections of 506–630GM by excitation of femtosecond laser at a wavelength of 800nm. 18–30-fold one-photon excited fluorescence (OPEF) enhancement and 300–450% TPEF increment binding with calf thymus DNA in Tris-HCl buffer solutions displayed obvious fluorescence “turn-on” effect. The co-localization studies showed mean co-localization coefficients of 0.88–0.94 by double-staining with commercial nuclear staining reagent DAPI in 3T3 cells, indicating accurate nuclear localization ability. The confocal fluorescence imaging displayed clear TPEF nuclear imaging. The staining penetration depth of 0–9μm exhibited good membrane permeability and three dimensional imaging ability. The observation time of 1800s and fluorescence decay amplitude of 8–10% within 300s under persistent irradiation were achieved in TPEF imaging for nuclear labeling. The DNA binding mechanism was discussed as well.

Synthesis, optical characterization, and solvatochromism study of new two-photon absorption compounds

The new donor-π-acceptor/acceptor-π-acceptor compounds (FQQ, KZQ, JYQ, and LVQ) were facilely synthesized and characterized by infrared, proton nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their UV-visible absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited fluorescence were systematically investigated in different solvents. The experiment results indicate that all these compounds exhibit relatively strong up-converted fluorescence and obvious solvatochromic effects. KZQ shows the largest σ value of 707 GM in THF upon 830 nm excitation. Its excellent optical properties provide a promising alternative as a polarity-sensitive two-photon fluorescent probe. Aided with the quantum chemical density functional theory calculations, the relationships between the structures and the properties were studied.

Inorganic nanoparticles for optical bioimaging

The tremendous progress in the synthesis of different inorganic nanoparticles with pretailored size, shape, structural, compositional, and surface properties has significantly raised their potential applications in biomedicine. Optically active inorganic nanoparticles are those that, based on inorganic materials, can produce fluorescence or scattered light under suitable optical excitation. These outgoing radiations can be conveniently used for bioimaging purposes. In this work, the different types of optically active inorganic nanoparticles that are being used for optical bioimaging are reviewed in detail. Special attention is paid to fluorescent and inorganic persistent luminescence nanoparticles and how their different excitation mechanisms (no-photon, one-photon, or multiphoton excited fluorescence) and working spectral ranges can be conveniently applied for in vitro and in vivo high-contrast optical bioimaging.

Hybrid polymeric nano-capsules loaded with gold nanoclusters and indocyanine green for dual-modal imaging and photothermal therapy.

Currently there is a great need to design nano-carriers which enable multi-modal imaging of tumors and administration of therapeutics with high efficacy simultaneously. Herein we report a facile and robust approach to fabricate multifunctional nano-capsules based on double emulsions. The hybrid nano-capsules were loaded with BSA capped gold nanoclusters (AuNCs) and indocyanine green (ICG) for dual-modal imaging and effective photothermal therapy. RGD peptides were conjugated onto the surface of the hybrid nano-capsules to target cells overexpressing integrin ανβ3. We demonstrated that the as-prepared nano-capsules can be used for both one-photon and two-photon fluorescence imaging of tumor cells, and subsequent photothermal ablation with high effectiveness. The background noise of tissue autofluorescence was dramatically suppressed in the two-photon imaging mode. Therefore, it assisted a great deal to acquire images with a high signal-to-noise ratio using the hybrid nano-capsules. Due to a unique combination of the one-photon/two-photon fluorescence imaging and highly-effective photothermal properties, the hybrid nano-capsules may find broad biomedical applications as attractive theranostic nanomaterials.

Computational design of zinc-ion-responsive two-photon fluorescent probes with conjugated multi-structures.

A series of conjugated multi-structured fluorescent probe molecules based on a salen ligand were designed and investigated in dimethyl sulfoxide solvent using a quantum-chemical method. The results indicate that the one-photon absorption and fluorescence emission spectra (λ (O) and λ (EM)) of these molecules generally show redshifts (of 23.1-74.5 and 22.7-116.6 nm, respectively) upon the coordination of the molecules to Zn(2+). Large Stokes shifts (1511.2-11744.1 cm(-1)) were found for the molecules, meaning that interference between λ (O) and λ (EM) can be avoided for these molecules. The two-photon absorption spectra of the molecules usually present blueshifts, but the two-photon absorption cross-section (δ) greatly increases (by 221.5-868.0 GM) upon the coordination of the molecules with Zn(2+). Most of the molecules show strong two-photon absorption peaks in the range 678.2-824.4 nm, i.e., in the near-infrared region. In a word, the expanded π-conjugated frameworks of these molecules lead to redshifted λ (O) and λ (EM) and enhanced δ values. Moreover, (L-phenyl)​2 and (L-phenyl-ethynyl)2 are the most suitable of the multi-structured molecules examined in this work for use as two-photon fluorescent probes for zinc ion detection in vivo. Graphical Abstract Scheme of the calculated transition energies (E0k and E0n) and the transition dipole moments (M0k and Mkn). NTO 109, NTO 197 and NTO 228 of Zn(L-phenyl-ethynyl), Zn2(L-phenyl-ethynyl)2 and Zn3(L-phenyl)3 for one-photon absorption, respectively.

Silole-Based Red Fluorescent Organic Dots for Bright Two-Photon Fluorescence In vitro Cell and In vivo Blood Vessel Imaging.

Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2 DTTPS), is synthesized and characterized. (MesB)2 DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2 DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 10(5) GM, which yields a two-photon action cross section of 1.09 × 10(5) GM. These (MesB)2 DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.

Efficient Two-Photon Fluorescent Probe for Nitroreductase Detection and Hypoxia Imaging in Tumor Cells and Tissues.

Hypoxia plays an important role in tumor progression, and the development of efficient methods for monitoring hypoxic degree in living systems is of great biomedical importance. In the solid tumors, the nitroreductase level is directly corresponded with the hypoxic status. Many one-photon excited fluorescent probes have been developed for hypoxia imaging in tumor cells via the detection of nitroreductase level. However, two-photon excited probes are more suitable for bioimaging. In this work, a two-photon probe 1 for nitroreductase detection and hypoxic status monitoring in living tumor cells and tissues was reported for the first time. The detection is based on the fact that the nitro-group of probe 1 could be selectively reduced to an amino-group by nitroreductase in the presence of reduced NADH, following by a 1,6-rearrangement-elimination to release the fluorophore, resulting in the enhancement of fluorescence. The probe exhibited both one-photon and two-photon excited remarkable fluorescence enhancement (∼70-fold) for nitroreductase, which afforded a high sensitivity for nitroreductase, with a detection limit of 20 ng/mL observed. Moreover, the applications of the probe for fluorescent bioimaging of hypoxia in living cells and two-photon bioimaging in tissues were carried out, with tissue-imaging depths of 70-160 μm observed, which demonstrates its practical application in complex biosystems.

A new series of two-photon blue/violet fluorescent trans-alkenes: Green synthesis and optical properties

A new series of trans-alkenes (3a–3e) containing different electron-donating groups were synthesized by the solvent-free Horner–Wadsworth–Emmons reaction, and characterized by infrared, hydrogen nuclear magnetic resonance, mass spectrometry and elemental analysis. Their UV–visible absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited fluorescence were systematically investigated in different solvents. Experimental results show different trends in linear and nonlinear optical properties with different donor units. 3a with triphenylamine donor exhibits the best optical properties. It emits strong blue up-converted fluorescence, and the two-photon absorption cross-section can be as large as 218 GM in DCM.

An effective colorimetric and ratiometric fluorescent probe for bisulfite in aqueous solution

We have developed the first two-photon colorimetric and ratiometric fluorescent probe, BICO, for the detection of bisulfite (HSO3−) in aqueous solution. The probe contains coumarin and benzimidazole moieties and can detect HSO3− based on the Michael addition reaction with a limit of detection 5.3 × 10−8 M in phosphate-buffered saline solution. The probe was used to detect bisulfite in tap water, sugar and dry white wine. Moreover, test strips were made and used easily. We successfully applied the probe to image living cells, using one-photon fluorescence imaging. BICO overcomes the limitations in sensitivity of previously reported probes and the solvation effect of bisulfite, which demonstrates its excellent value in practical application.

Localizable and photoactivatable fluorophore for spatiotemporal two-photon bioimaging.

Photoactivatable probe-based fluorescent imaging has become an efficient and attractive technique for spatiotemporal microscopic studies of biological events. However, almost all previously reported photoactivatable organic probes have been based on hydrosoluble precursors, which have produced water-soluble active fluorophores able to readily diffuse away from the photocleavage site, thereby dramatically reducing spatial resolution. Hydroxyphenylquinazolinone (HPQ), a small organic dye known for its classic luminescence mechanism through excited-state intramolecular proton transfer (ESIPT), shows strong light emission in the solid state, but no emission in solution. In this work, HPQ was employed as a precursor to develop a localizable, photoactivatable two-photon probe (PHPQ) for spatiotemporal bioimaging applications. After photocleavage, PHPQ releases a precipitating HPQ fluorophore which shows both one-photon and two-photon excited yellow-green fluorescence, thereby producing a localizable fluorescence signal that affords high spatial resolution for bioimaging, with more than 200-fold one-photon and 150-fold two-photon fluorescence enhancement.

Two-photon responsive metal-organic framework.

Two-photon processing presents a facile means to tailor the properties of materials in three-dimensions. A two-photon responsive metal-organic framework (MOF) has been realized through the incorporation of a photoactive linker into a MOF via a multivariate strategy. The resulting MOF exhibits a significant one-photon and two-photon excited fluorescence change in response to UV light and infrared femtosecond laser, enabling spatial modulation of the fluorescence property of the MOF. It thus demonstrates the capacity of two-photon patterning and imaging inside the crystal, and the formation of three-dimensional two-photon excited fluorescent structure in a high resolution.

The fluorescence and dynamics properties in phenoxy-phthalocyanines liquid

We investigated the one/two-photon fluorescence and excited state dynamics properties of two synthesized phenoxy-phthalocyanines (Pc1 and Pc2) using mild reaction coordination method. The results show that the fast decay component in the time-resolved fluorescence technique dynamics comes from the intramolecular vibrational relaxation, the slower ones from the internal conversion. Furthermore, in comparison with one-photon fluorescence spectra, the red shift of two-photon fluorescence spectra can be explained by the reabsorption effect of molecules. The samples are expected to be a potential candidate for optical applications and photodynamic therapy.

Correction to "Morphology and Carrier Extraction Study of Organic-Inorganic Metal Halide Perovskite by One- and Two-Photon Fluorescence Microscopy".

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.

Morphology and Carrier Extraction Study of Organic-Inorganic Metal Halide Perovskite by One- and Two-Photon Fluorescence Microscopy.

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.

Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

Four novel Zn(II) terpyridine complexes (ZnLCl2, ZnLBr2, ZnLI2, ZnL(SCN)2) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limiting (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations (TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence (OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080nm. These results revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior optical power limiting property.

Photoacoustic microscopy using ultrashort pulses with two different pulse durations.

We propose photoacoustic microscopy using ultrashort pulses with two different pulse durations in the range from femtoseconds to picoseconds. The subtraction of images for longer-pulse excitation from those for shorter-pulse excitation extracts two-photon photoacoustic images effectively, based on observation that the intensity ratio of two-photon to one-photon absorption-induced photoacoustic signals depends on the pulse duration in the same manner as the intensity ratio of two-photon and one-photon fluorescence signals. Two-photon photoacoustic microscopy using this subtraction method enables precise observation of the cross-sections of silicone hollows filled with the mixture of one-photon and two-photon absorption solutions.

Phototherapeutic functionality of biocompatible graphene oxide/dendrimer hybrids

Hydroxyl-terminated fourth generation poly(amido amine) dendrimer and folic acid were chemically bound on graphene oxide. The resultant hybrids exhibited one-photon and two-photon fluorescence emission, since the excitation irradiation at 390 and 780nm on the hybrids brought a fluorescence emission in the visible region around 450nm. In addition, the photocytotoxicity study revealed that under the two-photon excitation at 780nm, the hybrids can absorb near-infrared light and generate reactive oxygen species which can oxidize the HeLa cells and cause their death, suggesting the phototherapeutic behavior. Cytotoxicity measurement revealed the high biocompatibility of the hybrids toward HeLa cells. Thus, the present biocompatible hybrids consisting of only dendrimer, folic acid and graphene oxide have potentials as photodynamic therapeutic agents for medical treatment.