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Title: Ytterbium(III) porpholactones : β-lactonization of porphyrin ligands enhances sensitization efficiency of lanthanide near-infrared luminescence
Authors: Ke, XS
Yang, BY
Cheng, X
Chan, SLF 
Zhang, JL
Issue Date: 2014
Source: Chemistry - a European journal, 2014, v. 20, no. 15, p. 4324-4333
Abstract: The near-infrared (NIR) luminescence efficiency of lanthanide complexes is largely dependent on the electronic and photophysical properties of antenna ligands. Although porphyrin ligands are efficient sensitizers of lanthanide NIR luminescence, non-pyrrolic porphyrin analogues, which have unusual symmetry and electronic states, have been much less studied. In this work, we used porpholactones, a class of β-pyrrolic-modified porphyrins, as ligands and investigated the photophysical properties of lanthanide porpholactones Yb-1 a-5 a. Compared with Yb porphyrin complexes, the porpholactone complexes displayed remarkable enhancement of NIR emission (50-120 %). Estimating the triplet-state levels of porphyrin and porpholactone in Gd complexes revealed that β-lactonization of porphyrinic ligands lowers the ligand T1 state and results in a narrow energy gap between this state and the lowest excited state of Yb3+. Transient absorption spectra showed that YbIII porpholactone has a longer transient decay lifetime at the Soret band than the porphyrin analogue (30.8 versus 17.0 μs). Thus, the narrower energy gap and longer lifetime arising from β-lactonization are assumed to enhance NIR emission of Yb porpholactones. To demonstrate the potential applications of Yb porpholactone, a water-soluble Yb bioprobe was constructed by conjugating glucose to Yb-1 a. Interestingly, the NIR emission of this Yb porpholactone could be specifically switched on in the presence of glucose oxidase and then switched off by addition of glucose. This is the first demonstration that non-pyrrolic porphyrin ligands enhance the sensitization efficiency of lanthanide luminescence and also display switchable NIR emission in the region of biological analytes (800-1400 nm). Lanthanide porphyrinoids: Ytterbium porpholactones show enhanced sensitization efficiency for near-infrared luminescence of Yb3+, narrower energy gaps between the porphyrinoid T1 state and the lowest excited states of Yb 3+, and longer transient decay lifetimes than their porphyrin analogues (see figure). Furthermore, a glucose-conjugated water-soluble Yb porpholactone has potential applications as a switchable NIR-emissive probe.
Keywords: Biosensors
Publisher: Wiley-VCH
Journal: Chemistry - a European journal 
ISSN: 0947-6539
EISSN: 1521-3765
DOI: 10.1002/chem.201303972
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