Long-lived two-photon excited luminescence of water-soluble europium complex: applications in biological imaging using two-photon scanning microscopy

Photodynamic therapy and two-photon bio-imaging applications of hydrophobic chromophores through amphiphilic polymer delivery

The synthesis and photophysical properties of two lipophilic quadrupolar chromophores featuring anthracenyl (1) or dibromobenzene (2) were described. These two chromophores combined significant two-photon absorption cross-sections with high fluorescence quantum yield for 1 and improved singlet oxygen generation efficiency for 2, in organic solvents. The use of Pluronic nanoparticles allowed a simple and straightforward introduction of these lipophilic chromophores into biological cell media. Their internal distribution in various cell lines was studied using fluorescence microscopy and flow-cytometry following a successful staining that was achieved upon 2 h of incubation. Finally, multiphoton excitation microscopy and photodynamic therapy capability of the chromophores were demonstrated by cell exposure to a 820 nm fs laser and cell death upon one photon resonant irradiation at 436 ± 10 nm, respectively.

Lanthanide dota-like complexes containing a picolinate pendant: structural entry for the design of Ln(III)-based luminescent probes

In this contribution we present two ligands based on a do3a platform containing a picolinate group attached to the fourth nitrogen atom of the cyclen unit, which are designed for stable lanthanide complexation in aqueous solutions. Potentiometric measurements reveal that the thermodynamic stability of the complexes is very high (log K = 21.2-23.5), being comparable to that of the dota analogues. Luminescence lifetime measurements performed on solutions of the Eu(III) and Tb(III) complexes indicate that the complexes are nine coordinate with no inner-sphere water molecules. A combination of density functional theory (DFT) calculations and NMR measurements shows that for the complexes of the heaviest lanthanides there is a major isomer in solution consisting of the enantiomeric pair Λ(δδδδ) and Δ(λλλλ), which provides square antiprismatic coordination (SAP) around the metal ion. Analysis of the Yb(III)-induced paramagnetic shifts unambiguously confirms that these complexes have SAP coordination in aqueous solution. For the light lanthanide ions however both the SAP and twisted-square antiprismatic (TSAP) isomers are present in solution. Inversion of the cyclen ring appears to be the rate-determining step for the Λ(δδδδ) ↔ Δ(λλλλ) enantiomerization process observed in the Lu(III) complexes. The energy barriers obtained from NMR measurements for this dynamic process are in excellent agreement with those predicted by DFT calculations. The energy barriers calculated for the arm-rotation process are considerably lower than those obtained for the ring-inversion path. Kinetic studies show that replacement of an acetate arm of dota by a picolinate pendant results in a 3-fold increase in the formation rate of the corresponding Eu(III) complexes and a significant increase of the rates of acid-catalyzed dissociation of the complexes. However, these rates are 1-2 orders of magnitude lower than those of do3a analogues, which shows that the complexes reported herein are remarkably inert with respect to metal ion dissociation.

Synthesis and characterizations of star-shaped octupolar triazatruxenes-based two-photon absorption chromophores

A series of star-shaped octupolar triazatruxenes (TATs, 1-6) with intramolecular "push-pull" structure were synthesized and their photophysical properties have been systematically investigated. These chromophores showed obvious solvatochromic effect, i.e., significant bathochromic shift of the emission spectra and larger Stokes shifts were observed in more polar solvents mainly due to photoinduced intramolecular charge transfer (ICT). The two-photon absorption (2PA) cross-section values were determined by two-photon excited fluorescence (2PEF) measurements in toluene and THF. These chromophores exhibited large two-photon absorption cross-sections ranging from 280 to 1620 GM in the near-infrared (NIR) region. Compound 6 showed the largest 2PA action cross-section (σ(2)Φ) of 564 GM and could be a potential two-photon fluorescent (2PF) probe. In addition, compounds 1-6 all displayed good thermal stability and photostability.

Metal Ion-Responsive Fluorescent Probes for Two-Photon Excitation Microscopy

Metal ion-responsive fluorescent probes are powerful tools for visualizing labile metal ion pools in live cells. To take full advantage of the benefits offered by two-photon excitation microscopy, including increased depth penetration, reduced phototoxicity, and intrinsic 3D capabilities, the photophysical properties of the probes must be optimized for nonlinear excitation. This review summarizes the challenges associated with the design of two-photon excitable fluorescent probes and labels and offers an overview on recent efforts in developing selective and sensitive reagents for the detection of metal ions in biological systems.

High-fidelity hydrophilic probe for two-photon fluorescence lysosomal imaging

The synthesis and characterization of a novel two-photon-absorbing fluorene derivative, LT1, selective for the lysosomes of HCT 116 cancer cells, is reported. Linear and nonlinear photophysical and photochemical properties of the probe were investigated to evaluate the potential of the probe for two-photon fluorescence microscopy (2PFM) lysosomal imaging. The cytotoxicity of the probe was investigated to evaluate the potential of using this probe for live two-photon fluorescence biological imaging applications. Colocalization studies of the probe with commercial Lysotracker Red in HCT 116 cells demonstrated the specific localization of the probe in the lysosomes with an extremely high colocalization coefficient (0.96). A figure of merit was introduced to allow comparison between probes. LT1 has a number of properties that far exceed those of commercial lysotracker probes, including higher two-photon absorption cross sections, good fluorescence quantum yield, and, importantly, high photostability, all resulting in a superior figure of merit. 2PFM was used to demonstrate lysosomal tracking with LT1.

A europium complex with enhanced long-wavelength sensitized luminescent properties

We report a new complex Eu(tta)(3).bpt (tta = thenoyltrifluoroacetonate; bpt = 2-(N,N-di-ethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine) with excellent long-wavelength sensitized luminescent properties, in which four hydrogen atoms replace the methyl groups at the 3,3'- and 5,5'-positions of the pyrazolyl rings in a previously reported complex Eu(tta)(3).dpbt. Upon visible-light excitation (lambda(ex) = 410 nm) at 295 K, the quantum yield (Phi(Ln)(L)) of Eu(3+) luminescence of Eu(tta)(3).bpt is higher by 23% than that of Eu(tta)(3).dpbt. Different from the case of Eu(tta)(3).dpbt, Phi(Ln)(L) of Eu(tta)(3).bpt increases linearly with the decrease in temperature. Because of the different coordination environments around Eu(3+) ion, the fine structure of the hypersensitive (5)D(0)-->(7)F(2) emission band of Eu(tta)(3).bpt is quite different from that of Eu(tta)(3).dpbt, with the strongest emission line locating at 620 nm rather than 613 nm where the strongest emission line of Eu(tta)(3).dpbt appears. The excitation window of Eu(tta)(3).bpt is much broader than that of Eu(tta)(3).dpbt with a red edge extending up to 450 nm in a dilute toluene solution (1.0 x 10(-5) M) and 500 nm in a toluene solution (1.0 x 10(-2) M). Eu(tta)(3).bpt also exhibits excellent two-photon-excitation luminescent properties.

A two-photon europium complex as specific endoplasmic reticulum probe

Highly emissive europium complexes with specific endoplasmic reticulum localization potential includes several advantages such as fast uptake, long resident lifetime, low dosage requirement, low cytotoxicity and highly emissive two-photon induced f-f emission imaging.

Eu(III) Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance[]

The luminescence properties of lanthanoid ions can be dramatically enhanced by coupling them to antenna ligands that absorb light in the UV/visible and then efficiently transfer the energy to the lanthanoid center. The synthesis and the complexation of Ln(III) cations (Ln=Eu; Gd) for a ligand based on four 1-hydroxy-2-pyridinone (1,2-HOPO) chelators appended to a ligand backbone derived by linking two L-lysine units (3LI-bis-LYS) is described. This octadentate Eu(III) complex ([Eu(3LI-bis-LYS-1,2-HOPO)](-)) has been evaluated in terms of its thermodynamic stability, UV/visible absorption and luminescence properties. For this complex the conditional stability constant (pM) is 19.9, which is an order of magnitude higher than diethylenetriaminepentacetic acid (DTPA) at pH= 7.4. This Eu(III) complex also shows an almost two-fold increase in its luminescence quantum yield in aqueous solution (pH= 7.4) when compared to other octadentate ligands. Hence, despite a slight decrease of the molar absorption coefficient, a much higher brightness is obtained for [Eu(3LI-bis-LYS-1,2-HOPO)](-). This overall improvement was achieved by saturating the coordination sphere of the Eu(III) cation, yielding an increased metal centered efficiency by excluding solvent water molecules from the metal's inner sphere.