Wai-Sum Lo

Impressive Europium Red Emission Induced by Two-Photon Excitation for Biological Applications

Three triazine-based europium(III) complexes were synthesized that demonstrated strong two-photon induced europium emission with a high two-photon absorption cross-section. The modified triazine ligand of complex 3 initiated over 100% enhancement of the two-photon absorption cross-section (σ(2): 320 GM) when compared with complex 1 (σ(2): 128 GM) in a solution of DMSO. Europium complex 3 is also stable in vitro, and power-dependence curves were obtained in vitro to confirm the two-photon-induced f-f emission in HeLa cells.

Highly Luminescent SmIII Complexes with Intraligand Charge-Transfer Sensitization and the Effect of Solvent Polarity on Their Luminescent Properties

Samarium complexes with the highest quantum yields to date have been synthesized, and their luminescence properties were studied in 12 solvents. Sensitization via a nontriplet intraligand charge-transfer pathway was also successfully demonstrated in solution states with good quantum yields.

In Vitro Imaging and Human Serum Albumin Responsive Dimeric Lanthanide DO3A Complex

Two series of dimeric DO3A (1,4,7,10-tetraazacyclodecane-1,4,7-triacetate) lanthanide complexes (LnL(1)-LnL(2), Ln = Eu, Gd, and Tb) have been synthesized with two different bridged chromophores. The X-ray structures of dimeric LnL(1) (Ln = Gd and Tb) complexes show that each metal ion has nine coordination numbers with eight directly bound donor atoms of the ligand and one oxygen donor from the water molecule. Photophysical measurements indicate that the bridged antenna in LnL(2) gives a higher efficiency than that of LnL(1) and is responsive to the protein Human Serum Albumin (HSA), giving an f-f luminescence signal enhancement with a binding constant log K = 4.84. In vitro imaging of EuL(1) and EuL(2) in HeLa cells has been recorded, and EuL(2) has demonstrated a higher rate of cellular uptake and low cytotoxicity (IC(50) = 3 mM).

Photo-reactive charge trapping memory based on lanthanide complex

Traditional utilization of photo-induced excitons is popularly but restricted in the fields of photovoltaic devices as well as photodetectors, and efforts on broadening its function have always been attempted. However, rare reports are available on organic field effect transistor (OFET) memory employing photo-induced charges. Here, we demonstrate an OFET memory containing a novel organic lanthanide complex Eu(tta)3ppta (Eu(tta)3 = Europium(III) thenoyltrifluoroacetonate, ppta = 2-phenyl-4,6-bis(pyrazol-1-yl)-1,3,5-triazine), in which the photo-induced charges can be successfully trapped and detrapped. The luminescent complex emits intense red emission upon ultraviolet (UV) light excitation and serves as a trapping element of holes injected from the pentacene semiconductor layer. Memory window can be significantly enlarged by light-assisted programming and erasing procedures, during which the photo-induced excitons in the semiconductor layer are separated by voltage bias. The enhancement of memory window is attributed to the increasing number of photo-induced excitons by the UV light. The charges are stored in this luminescent complex for at least 104 s after withdrawing voltage bias. The present study on photo-assisted novel memory may motivate the research on a new type of light tunable charge trapping photo-reactive memory devices.

New Class of Bright and Highly Stable Chiral Cyclen Europium Complexes for Circularly Polarized Luminescence Applications

High glum values of +0.30 (ΔJ = 1, 591 nm, in DMSO) and -0.23 (ΔJ = 1, 589 nm, in H2O) were recorded in our series of newly designed macrocyclic europium(III) complexes. A sterically locking approach involving a bidentate chromophore is adopted to control the formation of one stereoisomer, giving rise to extreme rigidity, high stability, and high emission intensity. The combination of a chiral substituent on a macrocyclic chelate for lanthanide ions opens up new perspectives for the further development of circulary polarized luminescent chiral tags in optical and bioapplications.

Friend or foe? The role of solvents in non-triplet, intraligand charge transfer sensitization of lanthanide( iii ) luminescence

Sensitization of lanthanide luminescence in the visible and near infra-red (NIR) region was achieved via a non-triplet energy transfer pathway by long-wavelength excitation of an intraligand charge transfer (ILCT) band of a diethylamino-based ligand system. A comprehensive photophysical and solvatochromic study is conducted to evaluate the luminescence properties of our Eu(III), Sm(III) and Yb(III) complexes. The effects of solvent coordination and solvent quenching on lanthanide luminescence were studied in detail and efforts were also devoted into examining the ambiguous energy transfer mechanism of Yb(III) sensitization.

An efficient approach to synthesize glycerol dendrimers via thiol–yne “click” chemistry and their application in stabilization of gold nanoparticles with X-ray attenuation properties

We report here a facile, robust and efficient synthetic approach to glycerol dendrimers in different generations with up to 256 terminal groups, by using a light-mediated thiol–yne “click” reaction and propargylation in an iterative fashion. Neither transition metal nor heating is required during the syntheses. The synthesized first (G1), second (G2) and third (G3) generation dendrimers are well soluble in water and are demonstrated to be nontoxic to HeLa cells. These dendrimers are good organic nanotemplates in the stabilization of gold nanoparticles (AuNPs) in aqueous solution, and a series of narrowly-dispersed AuNPs (d = 1.2–8 nm) were prepared. These AuNPs with good stability exhibit X-ray attenuation properties and thus could be potentially used as computed tomography (CT) contrast agents. In this study, the developed glycerol dendrimers with alkyne or hydroxyl termini would be a good platform for the construction of multifunctional theranostic nanoagents for targeted drug delivery and imaging of diseases.

Gadolinium and Platinum in Tandem: Real-time Multi-Modal Monitoring of Drug Delivery by MRI and Fluorescence Imaging

A novel dual-imaging cisplatin-carrying molecular cargo capable of performing simultaneous optical and MR imaging is reported herein. This long-lasting MRI contrast agent (r1 relaxivity of 23.4 mM-1s-1 at 3T, 25 oC) is a photo-activated cisplatin prodrug (PtGdL) which enables real-time monitoring of anti-cancer efficacy. PtGdL is a model for monitoring the drug delivery and anti-cancer efficacy by MRI with a much longer retention time (24 hours) in several organs such as renal cortex and spleen than GdDOTA and its motif control GdL. Upon complete release of cisplatin, all PtGdL is converted to GdL enabling subsequent MRI analyses of therapy efficacy within its reasonably short clearance time of 4 hours. There is also responsive fluorescence enhancement for monitoring by photon-excitation.