Transient excited-state absorption and gain spectroscopy of a two-photon absorbing probe with efficient superfluorescent properties

The synthesis, linear photophysical properties, two-photon absorption (2PA), excited-state transient absorption, and gain spectroscopy of a new fluorene derivative tert-butyl 4,4'-(4,4' (1E,1'E)-2,2'-(9,9-bis(2- (2-ethoxyethoxy)ethyl)-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl)bis(4,1 phenylene)]dipiperazine-1-carboxylate (1) are reported. The steady-state linear absorption and fluorescence spectra, along with excitation anisotropy, fluorescence lifetimes, and photochemical stability of 1 were investigated in a number of organic solvents at room temperature. The 2PA spectra of 1 with a maximum cross-section of ~ 300 GM were obtained with a 1 kHz femtosecond laser system using open-aperture Z-scan and two-photon-induced fluorescence methods. The transient excited-state absorption (ESA) and gain kinetics of 1 were investigated by a femtosecond pump-probe methodology. Fast relaxation processes (~1-2 ps) in the gain and ESA spectra of 1 were revealed in ACN solution, attributable to symmetry-breaking effects in the first excited state. Efficient superfluorescence properties of 1 were observed in a nonpolar solvent under femtosecond excitation. One- and two-photon fluorescence microscopy imaging of HCT 116 cells incubated with probe 1 was accomplished, suggesting the potential of this new probe in two-photon fluorescence microscopy bioimaging.     

A mitochondrial-targeted two-photon probe for zinc ion

We report a two-photon probe (SZn-Mito) for mitochondrial zinc ions ([Zn2+]m). This probe shows a 7-fold enhancement of two-photon-excited fluorescence in response to Zn2+ with a dissociation constant (Kd(TP)) of 3.1 ± 0.1 nM and pH insensitivity in the biologically relevant range, allowing the detection of [Zn2+]m in a rat hippocampal slice at a depth of 100?200 μm without interference from other metal ions through the use of two-photon microscopy.     

A two-photon turn-on probe for glucose uptake

We report a two-photon turn-on probe (AS1) that can be excited by 780 nm femto-second pulses and visualize glucose uptake and the changes in the intracellular glucose concentration in live cells and tissue by two-photon microscopy.     

A specific probe for two-photon fluorescence lysosomal imaging

Lysosomes are vital organelles in physiological processes, as they receive and degrade macromolecules from the secretory and endocytic procedures. Evidences have shown that lysosomes were related to oncogenic activation and cancer progression, so lysosomes targeting and imaging probes make them convenient to be observed. In this study, a lysosome specific probe W-7 was designed and synthesized via convenient one-pot reaction and Heck reaction. This probe was derived from Tröger's base with a dimethylaminomethyl end group. The optical properties of this compound were measured. W-7 also showed two-photon absorption (TPA) effect by using laser excitation at the wavelength of infrared light. In vivo experiment, W-7 showed high specificity and selectivity for lysosomes in living cells (HeLa cells, MRC-5 cells and NRK cells), compared with LT Red, GT Red and MT Red (R = 0.96). Two-photon fluorescence images of HeLa cells stained by W-7 were obtained. And high resolution 3D reconstruction of lysosomes in one HeLa cell was provided by using two-photon confocal microscopy. The anantioseparation of racemic W-7 was carried out by chiral-HPLC, and the two enantiomers showed no significant difference in lysosomes imaging.     

A turn-on two-photon fluorescent probe for ATP and ADP

An acedan derivative containing Zn(II)-DPA has been developed as a two-photon probe for nucleoside phosphates, which shows enhanced fluorescence toward ATP and ADP at physiological pH 7.4 among other competing anions including AMP; the probe is permeable to cell membranes and thus can be directly used for two-photon imaging of ATP and ADP in live cells.     

Extended squaraine dyes with large two-photon absorption cross-sections

Extended bis(donor)-substituted squaraine chromophores exhibit very high two-photon cross-sections (as high as 33 000 GM) in the near-IR; these can be attributed to the combination of large transition dipoles with small detuning energies. The modulus of the third-order nonlinear optical susceptibility at 1.3 mum has been found to be 7.0 x 10-11 esu for one of these chromophores.     

A lysosomal polarity-specific two-photon fluorescent probe for visualization of autophagy

Autophagy plays a vital role in maintaining the balance of normal physiological state of living cells. In this paper, a polarity-specific two-photon fluorescent probe Lyso-NA based on naphthalimide was synthesized for the purpose of monitoring autophagy during biological research. The results of photophysical properties and theoretical calculation confirmed that different polarities of solvents mainly effected fluorescent intensities of probe. Fluorescent intensity, quantum yield and fluorescence lifetime of probe kept a good linear relationship with polarity respectively. In addition, due to its low toxicity and selective accumulation in lysosomes, Lyso-NA is suitable for detecting changes in lysosomal polarity of living cells. Compare with the imaging results of plasmid transfection, a better performed real-time long-term fluorescent visualization of autophagy in living cells was achieved. Probe Lyso-NA can work as an efficient and cost effective imaging tool for visualizing autophagy in living cells.     

A two-photon absorption cross section measurement in nitric oxide

We report here the measurement of a two-photon absorption cross section for the R₂₂ + S₁₂ (J″ = 9.5) [A ²Σ⁺ (ν′ = 0) - X ²Π (ν′ = 0)] transition in the gamma band system of nitric oxide by measuring the third-order susceptibility using a four-wave mixing technique. A value of σ⁽²⁾ = (1.0 ± 0.6) X 10^?38 πg(2ω₁ ? ω_f) cm⁴ s was obtained.     

A photochromic porphyrin-perinaphthothioindigo conjugate and its two-photon absorption properties

A porphyrin-perinaphthothioindigo conjugate having two-photon absorption cross-sections of approximately 2000 GM and approximately 700 GM for trans- and cis-isomers, respectively, was synthesized and exhibited clear photochromic behavior upon one-photon and two-photon excitation.     

Ratiometric detection of mitochondrial thiols with a two-photon fluorescent probe

We report a ratiometric two-photon probe (SSH-Mito) for mitochondrial thiols. This probe shows a marked blue-to-yellow emission color change in response to RSH, a significant two-photon cross section, good mitochondrial thiol selectivity, low cytotoxicity, and insensitivity to pH over the biologically relevant pH range, allowing the direct visualization of RSH levels in live cells as well as in living tissues at 90-190 μm depth without interference from other biologically relevant species through the use of two-photon microscopy.     

Ultrafast dynamics in multibranched structures with enhanced two-photon absorption

The understanding of the mechanism of the enhanced two-photon absorption (TPA) in multibranched chromophore systems is of importance to the design of materials with the large TPA cross-sections and for future applications. In this communication, the mechanism of enhanced TPA properties is investigated. For a dendritic model system, the excited-state dynamics for both population (T1-process) and phase relaxation (T2-process) processes involved are investigated by a combination of time-resolved spectroscopic techniques. The results of time-resolved fluorescence anisotropy are compared with previous results obtained from other branched chromophore systems. It is found that the PRL-701 trimer system, which possesses the large enhancement of two-photon absorption cross-section, gives a faster anisotropy decay (fluorescence upconversion and transient absorption), a longer population relaxation time (fluorescence lifetime), and a weaker coupling to the solvent (a larger photon echo peak shift initial value). New strategies for rational design of large TPA materials can be achieved based on a better understanding of the mechanism of the enhancement.     

Triphenylamine derivatized phenylacetylene macrocycle with large two-photon absorption cross-section

A phenylacetylene macrocycle (PAM) derivative containing triphenylamine as the framework was synthesized in one-step Sonogashira coupling. The photophysical and electrochemical properties were investigated in details. This hexamer shows significant enhancement in two-photon absorption cross-section relative to reported PAM derivatives.     

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activity

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.     

A small molecule two-photon probe for hydrogen sulfide in live tissues

We report a two-photon probe (FS1) which shows a 21-fold two-photon excited fluorescence enhancement in response to H(2)S and can selectively detect H(2)S in a rat hippocampal slice at a depth of 90-190 μm by using two-photon microscopy.     

Molecular proximity effects in two-photon absorption

Under laser irradiation, the mutual interaction between molecules is shown to lead to a cooperative nonlinear process which results in entirely new features in the absorption spectrum. In the quantum electrodynamical formalism the coupling between molecular centres, induced by molecular proximity rather than collision, is mediated by means of virtual photon coupling and allows transitions which are forbidden in the absence of such interactions. The manifestation of circular dichroism, potential methods of observation and specific molecular examples are discussed. Attention is drawn to a number of possible resonance enhancement mechanisms and to the dependance of the absorption rate of molecular separation.     

Detection of nickel in fish organs with a two-photon fluorescent probe

Molecular imaging by two‐photon microscopy (TPM) has become indispensable to the study of biology/medicine owing to its capability of imaging deep inside intact tissues. To make TPM a more‐versatile tool, a large variety of two‐photon probes are needed. Herein, we report a new two‐photon fluorescent probe (ANi2) that can be excited by 750 nm femtosecond pulses and detect Ni²⁺ ions in fresh fish organs at 90–175 μm depth without interference from the pH value or from other biologically relevant species through the use of TPM. TPM images of fish organs labeled with ANi2 revealed that Ni²⁺ ions accumulate in fish organs in the order: kidney > heart > gill ≥ liver. Moreover, a linear relationship was found between the two‐photon‐excited fluorescence (TPEF) and the inductively coupled plasma mass spectrometry intensities (ICP‐MS), thereby allowing the quantitative measurement of Ni²⁺ ions in live tissue.     

Novel 2,1,3-benzothiadiazole-based red-fluorescent dyes with enhanced two-photon absorption cross-sections

This paper reports the two-photon absorbing and orange-red fluorescence emitting properties of a series of new 2,1,3-benzothiadiazole (BTD)-based D-pi-A-pi-D-type and star-burst-type fluorescent dyes. In the D-pi-A-pi-D-type dyes 1-6, a central BTD core was connected with two terminal N,N-disubstituted amino groups via various pi-conjugated spacers. The star-burst-type dyes 8 and 10 have a three-branched structure composed of a central core (benzene core in 8 and triphenylamine core in 10) and three triphenylamine-containing BTD branches. All the BTD-based dyes displayed intense orange-red color fluorescence in a region of 550-689 nm, which was obtained by single-photon excitation with good fluorescent quantum yield up to 0.98 as well as by two-photon excitation. Large two-photon absorption (TPA) cross-sections (110-800 GM) of these BTD dyes were evaluated by open aperture Z-scan technique with a femtosecond Ti/sapphire laser. The TPA cross-sections of D-pi-A-pi-D-type dyes 2-6 with a benzene, thiophene, ethene, ethyne, and styrene moiety, respectively, as an additional pi-conjugated spacer are about 1.5-2.5 times larger than that of 1c with only a benzene spacer. The TPA cross-sections significantly increased in three-branched star-burst-type BTDs 8 (780 GM) with a benzene core and 10 (800 GM) with a triphenylamine core, which are about 3-5 times larger than those of the corresponding one-dimensional sub-units 9 (170 GM) and 11 (230 GM), respectively. The ratios of sigma/e(pi) between three-branched and one-dimensional dyes were 6.5:3.8 (for 8 and 9) and 6.0:4.0 (for 10 and 11), which are larger than those predicted simply on the basis of the chromophore number density (1:1), according to a cooperative enhancement of the two-photon absorbing nature in the three-branched system.     

A bright two-photon fluorescent probe for real-time monitoring autophagy in living cells

A novel donor-acceptor(D-A) type of two-photon(TP) fluorescent probe,i.e.Lyso-OSC,based on the lysosome-targeting morpholine group was developed.The polarity sensing coumarin group was functionalized as the acceptor and the 1-vinyl-4-methoxybenzene group was engineered as the donor.The fluorescence intensity and emission maximum wavelength of Lyso-OSC are highly sensitive to the polarity changes of solvent.The two-photon absorption cross-section and tissue penetration depth are up to 254 GM and 150 μm,respectively.The strong fluorescence,high sensitivity to polarity,low cytotoxicity,and accurate lysosome-targeting ability entail Lyso-OSC the excellent performance in detecting the polarity changes ofcellular environment.To this end,a bright,real-time imaging autophagy of living cells has been achieved.