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Phosphorescent materials based on cyclometalated platinum complexes have attracted a great deal of attention because of their potential in chemical, biological and optoelectronic applications, specifically as emitters in organic light-emitting diode devices. In addition, development of phosphorescent materials emitting in the deep red and/or near infrared region have become a popular area of focus because of their capabilities as chemosensors, in solar cells and bioimaging dyes. Several classes of phosphorescent cyclometalated platinum complexes based on tridentate and tetradentate ligands have already been developed by our lab. In this study, two series of cyclometalated N^N^C Pt(II) complexes 1a-6a and 1b-6b, were designed to emit throughout a wide range of the visible spectrum and were successfully synthesized bearing either a phenyl acetylide or phenyl ancillary ligand. The photophysical properties of complexes can be tuned as desired through methodical modifications of the cyclometalating or ancillary ligand with varying electron accepting or donating moieties. Photophysical studies were conducted on the synthesized complexes and found emission wavelengths ranging from 496-643 nm, quantum yield ([Phi]p) values between 43.0% and [less than] 0.1% and lifetimes ([tau]) as long as 13.1 [micro]s at 298 K. TD-DFT calculations of ground state HOMO and LUMO orbitals, as well as X-ray crystallographic analysis of select complexes were conducted and analyzed. The data comparison of the obtained results between the phenyl acetylide and phenyl coordinated complexes assists in identifying any structure-photophysical property relationships present, which will be discussed in detail.
The synthesis, structure, and photophysical properties of luminescent platinum (II) complexes with different coordination patterns, (C^C*N^N), (N^C*N), (N^N*C) and (N^N^C) are reported, where "C^N or N^N" denotes a bidentate coordination to the platinum to form a five-membered metallacycle and "C*N" denotes a bidentate coordination to the platinum to form a six-membered metallacycle. Sixteen cyclometalated platinum complexes have been synthesized with different coordination patterns, which include six complexes with tridentate N^C*N cyclometalating ligands (13, 14, 15, 16, 17, and 18), five complexes with N^N*C cyclometalating ligands (19a, 19b, 20a, 20b, and 24), three complexes with N^N^C cyclometalating ligands (21a, 21b, and 29) and two complexes with tetradentate C^C*N^N cyclometalating ligands (33 and 34). The structures of the platinum complexes 13, 15, 16, 18, 19a, 19b, 20a, 21a, 21b, 24, 29, 33, and 39 were determined by single crystal X-ray diffraction. In platinum complexes with five-six membered metallacycle (15, 16, 18, 19a, 19b, 20a, 24, and 39), the square geometry of the complexes is improved when compared to that of platinum complexes with five-five membered metallacycle as the biting angle is increased. The tetradentate coordination (C^C*N^N), square planar geometry of complex 33 are revealed from its X-ray crystal structure. The DFT calculations have been carried out on complexes 13, 14, 15, 16, 17, 18, 33, and 34 to examine the molecular orbital character of the complexes, which are used in interpreting the electronic spectra of the complexes. The photophysical properties of the platinum complexes were studied and a majority of the complexes were highly emissive in solution at room temperature. Complex 13 exhibited the highest quantum yield (65%) among all of the complexes. Self quenching was not observed in a majority of the platinum complexes at lower concentrations. The cytotoxicity (IC50) of the complexes in three lung cancerous cell lines and one prostate cancer cell line were determined by MTT assay. The toxic platinum complexes induced the cell death by triggering apoptosis. The interactions of the platinum complexes with plasmid and calf thymus DNA were studied. Activation of caspase -7, PARP, and p53 were also observed in RV1 and HCC827 cell lines when treated with platinum complexes. Complexes 35, 37 and 38 were more potent than the clinically approved drug, cis-platin.
The synthesis, structure, and photophysical properties of a series of novel, highly luminescent tridentate platinum complexes with general coordination geometry of (C^N*N)-PtL are reported, where "C^N" denotes a coordination of C and N to the platinum to form a five-membered metallacycle and "N*N" denotes a coordination of two N atoms to the platinum to form a six-membered metallacycle; L is a mono anionic ligand such as halides or acetylides. Compared to the known (C^N^N)-PtL type of complexes that were reported to emit with low quantum yields, the structural modification leads to dramatic improvements in phosphorescence efficiency. For example, new complexes (C^N*N)-PtL with L = hexylacetylide and phenylacetylide emitted intensely with quantum yields of 47% and 56%, respectively, latter of which is among the highest quantum yields reported so far for cyclometalated platinum (II) complexes. Selectivity in C-H bond activation by platinum and the exact mechanism of cycloplatination are issues that still remain unclear. A series of ligands which include sp2/sp3, primary/secondary sp3 C-H bonds, and aromatic/vinylic sp2 C-H bonds with a carbon linker between the bipyridine and the carbon groups have been prepared. All ligands have been attempted for cycloplatination in glacial acetic acid and acetonitrile. All ligands produced the same sp2 C-H bond activated complex in both solvents, which suggests that the linker atom does play a role on selectivity.
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The present dissertation describes the synthesis, photophysical, and electrochemical properties of a library of pyrazolate-bridged dinuclear cyclometalated platinum(II) complexes. All the complexes investigated here were synthesized with complete characterization. Both the steady state, as well as the time-resolved photophysical techniques employed during the study, helped in defining the photophysical behavior exhibited by such complexes. All the dinuclear Pt(II) complexes discussed here can be expressed by a general formula [Pt(C^N)(µ-R2pz)]2; where C^N is a cyclometalating ligand, and R2Pz are various 3,5-disubstituted pyrazolates. The bridging pyrazolates initiates the metal-metal interaction by building up steric strain within the resulting A-frame topology of the complexes. All the Pt(II) complexes are strongly emissive at room temperature. The influence of the nature of cyclometalating ligand, and the bridging pyrazolates on the photophysical and electrochemical behavior displayed by the complexes were thoroughly investigated. Both room temperature and low temperature measurements aided in distinguishing the nature of lowest energy emissive state present in such complexes. The second part of this dissertation merges our research interest in metal-organic light harvesting chromophores and MLCT complexes with extended lifetime. The dinuclear platinum(II) complexes investigated, have a 4-piperidinyl-1,8-naphthalimide (PNI) unit covalently attached to the cyclometalating 2-phenylpyridine ligand. The resulting bichromophoric complex displayed an enhanced light harvesting ability as compared to the parent dimers. Our study is an effort towards understanding the influence of increased metal-metal interaction on the establishment of a thermal equilibrium between the 3PNI and the 3MMLCT excited states.
Aryl group can indeed be transferred into platinum metal having strong phosphine ligand provided that Cu(I) salts used as catalyst. Different ligands were tested to investigate the scope of the reaction, a library of monosubstituted, symmetrically disubstituted and asymmetrically disubstituted platinum complexes were prepared. Basic photophysical properties i.e. ground-state absorption, steady-state emission in both air-saturated and argon purged solutions were studied. Finally, the novel carbon-platinum bond formation reaction was used to synthesize a series of platinum complexes in which 2,1,3-benzothiadiazole was ligated with various electron-rich systems was connected via platinum metal. Extensive photophysical and electrochemical investigation was conducted on these novel platinum complexes.