Photophysical Properties and Applications of Lanthanoid Helicates - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 192

ESA excited state absorption

ETU energy transfer upconversion

oppert-Mayer unit: 10 50 cm 4 sphoton 1 for 2PA and 10 83 cm 6 GM G

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s 2 photon 2 for 3PA
Her2/ neu human epidermal growth factor receptor
HHH head to head to head arrangement of ligand strands
IgG immunoglobulin G
JO Judd-Ofelt
LIS lanthanoid-induced shift
LMCT ligand-to-metal charge transfer
LOD limit of detection
mAb monoclonal antibody
MALDI-TOF matrix-assisted laser desorption - ionization time of flight mass
spectrometry

MD magnetic dipole

MLCT metal-to-ligand charge transfer

NIR near infrared

NMR nuclear magnetic resonance

NP nanoparticle

pet photoinduced electron transfer

PCR polymerase chain reaction

TL total luminescence

tpy terpyridine

TRD time-resolved detection

TRLM time-resolved luminescence microscopy

WST-1 water-soluble tetrazolium salts

YAG yttrium aluminum garnet

6.1 Introduction

A helicate is a discrete coordination compound constituted by one or more organic
covalent strand(s) wrapped helically around at least two metal centres defining the helical
axis [1]. Additionally, weak interactions programmed between the ligand strands lead to
supramolecular recognition of the metal ions. The first helicates synthesized by J.-M.
Lehn in 1987 contained d-transition metal ions. The fact that ions with spherical elec-
tronic density such as Cu I ,Zn II or Ga III easily self-assemble with polytopic ligands bear-
ing adequate coordination groups to yield double- or triple-stranded polynuclear helicates
opened perspectives for tailoring helical edifices in which the metal ions are trivalent lan-
thanoid ions (Ln III ). These ions have a [Xe]4f n electronic configuration, so that 4f elec-
trons are shielded from external interactions by the filled 5s 2 5p 6 electronic subshells.
Consequently, they are large, spherical and labile so that the polytopic ligands encapsulat-
ing them have to be carefully designed. Interest for lanthanoid helical complexes started
in 1992 when the group of E. Constable showed the helical wrapping of sexipyridine
around Eu III in [Eu(NO 3 ) 2 (L1)](PF 6 ) [2]. The same year, Xing Ya Cheng et al. and C.
Piguet et al. reported the first tripled-stranded dinuclear lanthanoid helicates. The Chinese