Yingying Ning

Design of Near-Infrared Luminescent Lanthanide Complexes Sensitive to Environmental Stimulus through Rationally Tuning the Secondary Coordination Sphere

The design of near-infrared (NIR) emissive lanthanide (Ln) complexes sensitive to external stimulus is fundamentally important for the practical application of Ln materials. Because NIR emission from Ln is extremely sensitive to X-H (X = C, N and O) bond vibration, we herein report to harness the secondary coordination sphere to design NIR luminescent lanthanide sensors. Toward this goal, we designed and synthesized two isomeric [(η5-C5H5)Co{(D3CO)2P = O}3]-Yb(III)-7,8,12,13,17,18-hexafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porpholactol NIR emitters, Yb-up and Yb-down, based on the stereoisomerism of porphyrin peripheral β-hydroxyl group. Yb-up, in which β-OH is at the same side of Yb(III) center, can form an intramolecular hydrogen bond with the axial Kläui ligand, whereas Yb-down cannot because its β-OH is opposite to Yb(III) center. X-ray crystal structures and photophysical studies suggested that the intramolecular hydrogen bond plays important roles on the NIR luminescence of ytterbium(III), which shortens the distance between β-OH and Yb(III) and facilitates the nonradiative deactivation of Ln excited state. Importantly, Yb-up/down were demonstrated to be highly sensitive toward temperature and viscosity. The PMMA polymer using Yb-up as the dopant NIR emitter showed thermosensitivity up to 6.0% °C-1 in the wide temperature range of 77-400 K, higher than that of Yb-down (3.8% °C-1). These complexes were also explored as the first NIR viscosity sensor, revealing their potential applications as optical sensors without visible light interference. This work demonstrates the importance of secondary coordination sphere on designing NIR Ln luminescent functional materials.

β-Fluorinated porpholactones and metal complexes: synthesis, characterization and some spectroscopic studies

We describe the synthesis of β-fluorinated porpholactones by oxidation of the fluorinated CC bond of the pyrrolic subunit in porphyrin using the “RuCl3 + Oxone®” protocol. The electron-withdrawing effects of β-fluorine on the absorption, fluorescence, phosphorescence and redox properties of the β-fluoroporpholactones were studied. A potential application of the β-fluoroporpholactones was demonstrated in sensitizing near-IR (NIR) emissive ytterbium, giving a high quantum yield (58%) and long luminescence time (525 μs) in CD2Cl2.

The design of rigid cyclic tripyrrins: the importance of intermolecular interactions on aggregation and luminescence

We designed a cyclic tripyrrin “locked” by a bridging benzene-1,4-diol-moiety which is perpendicular to the tripyrrin plane. The cyclic structures promote the scaffold rigidity and enhance the fluorescence. While the halogen-substitution of the bridging moiety was found to slightly affect the fluorescence of 1–3 in solution, such substitution significantly affects the aggregation behaviour and solid emission. 1 and 2 exhibit typical J-aggregate emission but 3 does not. The analysis of crystal packing combined with the reduced density gradient (RDG) analysis suggests that the bridging moieties of 1–3 play an important role in inducing the different crystal packing by tuning intermolecular interactions in the solid state. The energy decomposition analysis using symmetry adapted perturbation theory (SAPT) revealed that such weak intermolecular interactions mainly consist of halogen bonds and π–π interactions.

Lutetium(III) porphyrinoids as effective triplet photosensitizers for photon upconversion based on triplet-triplet annihilation (TTA)

We described the first application of lanthanide complexes of porphyrinoids, exemplified by lutetium (Lu), as efficient photosensitizers in photon upconversion (UC) based on triplet–triplet annihilation (TTA). Compared to the widely used d block metals, Lu(III) porphyrinoids exhibit a better sensitization ability in photon UC based on TTA (TTA-UC), which is ascribed to the extra-long triplet lifetime compared with the d block metal counterparts, using 9,10-bis(2-phenylethynyl)anthracene (BPEA) or rubrene as an acceptor. Notably, the Lu(III) complex of the porphyrin (Lu-1)/BPEA pair showed a high upconversion efficiency of 12.4% in degassed toluene. Importantly, to demonstrate the potential application of Lu porphyrinates in TTA-UC based bioimaging, we prepared nanomicelles and mesoporous silica nanoparticles with Lu-1/BPEA or Lu(III) porpholactone (Lu-2)/BPEA pairs. In living cell imaging, the capability of Lu-1 or Lu-2 as a TTA-UC sensitizer has been observed, displaying their potential application in biological studies. This work enriches the repertoire of metal sensitizers in TTA-UC with the capability of living cell imaging and, more importantly, also extends the scope of lanthanide coordination chemistry to lanthanide chemical biology related to biological optical materials and medicine.

Synthesis, characterization and reactivity of trans-dihydroxy platinum(IV) porphyrins

Synthesis of two trans-dihydroxy platinum(IV) porphyrins (TPP, tetraphenylporphyrin and F20TPP, tetrakispentafluorophenylporphyrin) by dimethyl dioxirane (DMD) oxidation of their PtII porphyrin precursors have been described. The oxidation state of Pt cation in such complexes was assessed by X-ray photoelectron spectroscopy and shown to be +4. More importantly, proton was found to promote the formation and stabilization of the trans-dihydroxy platinum(IV) porphyrins, as revealed by UV-vis spectroscopic results and single crystal structures. In addition, these trans-dihydroxy PtIV porphyrins were much easier to be reduced than their Pt(II) counterparts and capable to transfer oxygen atom to triphenylphosphine and thioanisol, which is important for further application of Pt(IV) complexes in catalytic reactions.