Phosphorescent platinum(ii) complexes containing different β-diketonate ligands: synthesis, tunable excited-state properties, and their application in bioimaging

Abstract

A series of square-planar Pt(II) complexes [Pt(C^N)(O^O)] (1-5) (C^N ¼ 2-phenylpyridine, O^O denotes a series of b-diketonate ligands) is reported. Detailed studies of theoretical calculations, electrochemical and photophysical properties have shown that their excited states can be attributed to the mixing of 3 MLCT, 3 LLCT and 3 LC/ 3 ILCT transitions. For 1, the excited state is dominated by the C^N ligand. The excited states of complexes 2-5, however, are dominated by O^O ligands. Through variation of the b-diketonate ligands, the emission colors of 1-5 can be tuned from blue-green to yellow. Further investigations have revealed that the emission of 4 in the solid state can be attributed to the 3 MLCT and 3 LLL'CT transitions, which has been confirmed by X-ray diffraction studies as well as theoretical calculations. Moreover, exclusive staining of cytoplasm and low cytotoxicity have been observed for 1-4, which makes them promising candidates as phosphorescent probes for bioimaging.

HOMO–LUMO energy gap control in platinum(ii) biphenyl complexes containing 2,2′-bipyridine ligands

“…Square planar complexes of platinum(II) containing a biphenyl dianion ligand and the other ligand being diimine, 1,2,3,4 phosphine, 5 pyridyl, 6 acetonitrile, 6,7 CO, 8,9 or diene, 10,11 as well as complexes containing η 1 -biphenyl monoanion 12 and phenylpyridine 13,14 ligands have been attractive to researchers due to potential applications in photocatalytic, 5,15 optoelectronic, 16,17,18 chemosensory, 1,13 and biomedical imaging devices. 14 This research interest is largely due to the significant Stokes shift, tunable emission wavelengths and high photoluminescence efficiency of these compounds.…”

Oxygen and temperature sensitivity of blue to green to yellow light-emitting Pt(ii) complexes

“…12,[30][31][32][33] The strong absorption for all complexes 1-5 at 225-345 nm can be related to spin-allowed ligand-centered transitions (π → π*), which are the expected absorption bands in this region. 18,34,35 Solvatochromatic metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) transitions are located between 350 and 450 nm. 18,12 The β-diketonato ligand has no detectable influence on the luminescence properties of the excited state.…”

“…18,34,35 Solvatochromatic metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) transitions are located between 350 and 450 nm. 18,12 The β-diketonato ligand has no detectable influence on the luminescence properties of the excited state. 1,5,6,12 The emission of the complexes 1-5 is due to a mixed 3 LC-MLCT state 12 and the particular effects of the respective C^N substituents can directly be seen in the emission spectra (Fig.…”

“…1,11,12 As a consequence of their favourable properties, it has already been demonstrated that platinum(II) complexes can be beneficially applied to chemosensors, 13 light-emitting devices, 14 photovoltaics 15,16 and colorimetric oxygen sensors, 17 and, due to their good cell membrane permeability, also in imaging of living cells. 18 Moreover, Pt(II) complexes are also promising indicators for optical dual oxygen and temperature sensors, if they can be combined with a second indicator and the resulting pressure and temperature signals can be separated by optical filters. This can be achieved, if the indicators emit at sufficiently different wavelengths without spectral overlap.…”

Potential strategy used for controlling the phosphorescent properties in tetradentate Pt(II) complexes: Effect of azole ligand

“…In the past few decades, transition metal complexes have aroused extensive interest and attention, they are widely used in the field of organic light‐emitting diodes (OLEDs) . Because Pt(II) and Ir(III) can introduce a strong spin–orbit coupling (SOC) effect, causing the effective intersystem crossing between singlet (S n ) and triplet (T n ) excited states and partial allowance of T n (usually, n = 1) → ground state transition, Pt(II) and Ir(III) complexes are regarded as the most popular emitters in OLEDs.…”