Synthesis, Structure, And Properties Of Tridentate Pt(Ⅱ) Complexes Of Triazolyl/Carboxylato-bipyridine

Square-planar d8platinum(Ⅱ) complexes have recently received a great deal of attention inview of their rich and unique photophysical properties and promising applications in many fields,such as in luminescent devices, optical sensors, and solar energy conversion materials. In this thesis,four tridentate chelating ligands and ten tridentate platinum(Ⅱ) complexes have been designed andthesised. The structures and photophysical properties of these Pt(Ⅱ) complexes have beeninvestigated by single-crystal X-ray diffraction, nuclear magnetic resonance spectroscopy, massspectroscopy, elemental analysis, UV-Vis spectroscopy, fluorescence spectroscopy.Two new Pt(Ⅱ) chlorido complexes Pt(ftbpy)Cl (1) and Pt(ftmbpy)Cl (2) with deprotonated6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-2,2′-bipyridine (ftbpyH) and6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine (ftmbpyH) terdentate ligands has been synthesized andcharacterized. Complex2gives a distorted square-planar configuration with a mono-anionicchelate ftmbpy, and displays a1-D zigzag head-to-tail arrangement along the b axis formed viaintermolecular π···π stacking and Pt···Pt interactions. A relatively weak broad absorption isobserved at360~435nm in dilute CH2Cl2solution at room temperature for1and2, tentativelyascribed to the metal-to-ligand charge transfer (1MLCT) excited state with some mixing of intra-ligand1ππ*character inside ftmbpy, as supported by TD-DFT analysis. It is demonstrated thatcomplex2is emissive in both solution and solid states and exhibits the concentration-dependentluminescence properties originating from intermolecular Pt···Pt and π···π interactions, and theintroduction of substituents (e.g. two methyl groups) into the2,2′-bipyridyl ring is effective forimproving the solubility of Pt(Ⅱ) complexes and leads to the blue-shifting of the emission ofcomplex2relative to complex1.Two platinum(Ⅱ) complexes [Pt(ftmbpy)PPh3](ClO4)(3) and [Pt(ftmbpy)2(μ-dppm)](ClO4)2(4) have been afforded via the reaction of complex2with PPh3and dppm, respectively. Asrevealed by single-crystal X-ray diffraction, complex3adopts a distorted square-planararrangement generated by three N atoms of ftmbpy and one P atom of PPh3. A weak broadabsorption is observed at355~450nm in CH2Cl2solution for3, tentatively ascribed to the metal-to-ligand charge transfer (1MLCT) state with some mixing of intra-ligand1ππ*character insideftmbpy. A weak broad absorption of complex4is observed at360~430nm, tentatively assigned tothe metal–metal-to-ligand charge transfer (1MMLCT) state with some mixing of the intra-ligand 1ππ*character inside ftmbpy. The luminescence of complex4is red-shifted compared to complex3. The solution emissions of complexes3and4are all blue-shifted relative to their respectivesolid-state emissions.Using two chelating ligands6-methoxycarbony-2,2′-bipyridine and6-methoxycarbony-4,4′-dimethyl-2,2′-bipyridine, three Pt(Ⅱ) complexes Pt(bpyc)Cl (5), Pt(mbpyc)Cl (6), and[Pt(mbpyc)PPh3](ClO4)(7) have been synthesized. As revealed by single-crystal X-ray diffraction,complex7adopts a distorted square-planar N2OP arrangement generated by one O atom and two Natoms of4,4′-dimethyl-2,2′-bipyridine-6-carboxylate (mbpyc) and one P atom of PPh3. A weaklowest-energy absorption is observed at320~450nm in CH3CN solution for5–7, which is affectedby the substituents of tridentate chelating ligand and ancillary ligand and is ascribed to metal-to-ligand charge-transfer (1MLCT) transitions mixed with ligand-to-ligand charge-transfer (1LLCT)and intra-ligand charge-transfer (1ILCT) characters, as supported by the TD-DFT calculations.Complexes5–7have the luminescence properties in solid state at ambient temperature, which isalso influenced by ancillary ligand and the substituents of tridentate chelating ligand.Three pyrazolate-linked dinuclear platinum(Ⅱ) complexes [Pt(bpyc)(μ-dmpz)]2(8),[Pt(bpyc)(μ-pz)]2(9), and [Pt(mbpyc)(μ-dmpz)]2(10) have been prepared via the reaction ofcomplexes5and6with pyrazol (pz) and3,5-dimethyl-pyrazol (dmpz), respectively. Thepyrazolate-bridged di-Pt(Ⅱ) complexes8and10give a boat-like conformation. The introductionsof two methyl groups into the ligand almost have no effect on the luminescence properties ofcomplexes810. The pyrazolate bridge controls the Pt···Pt distances of complexes810, and theabsorption and emission bands red-shift with the decreasing Pt···Pt distance. Complexes8and9are all luminescent in CH3CN solution, and their emissive states are tentatively ascribed to metal–metal-to-ligand charge transfer3MMLCT transitions.