Synthesis and spectroscopic studies of cyclometalated Pt(II) complexes containing a functionalized cyclometalating ligand, 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine.
Three new luminescent cyclometalated Pt(II) complexes, [Pt(L)Cl] (1), [Pt2(L-)2] (2), and [Pt(L)(PPh3)]ClO4 (3.ClO4) (where HL=2-phenyl-6-(1H-pyrazol-3-yl)-pyridine), were synthesized and characterized by X-ray crystallography. HL represents a new class of C,N,Npyrazolyl cyclometalating ligands containing a Cphenyl, a Npyridyl, and a Npyrazolyl donor moiety, as well as a 1-pyrazolyl-NH, that can also be available for metal coordination and other chemical interactions. Complex 1 possesses intense intraligand transitions at 275-375 nm and moderately intense metal-to-ligand charge transfer (1MLCT) (dpi(Pt)-->pi*(L)) transition at 380-410 nm. The room temperature solid-state emission lambdamax of 1 occurs at 580 nm and is attributable to the 3MMLCT (dsigma*(Pt)-->pi*(L)) transition. It also displays strong phosphorescence in acetonitrile solutions at room temperature with an emission lambdamax at 514 nm, which can be tentatively assigned to the 3MLCT (pi*(L)-->dpi(Pt)) transition. Complex 1 can be deprotonated in organic solvents to yield a cycloplatinated dimer 2, which shows a relatively high room-temperature luminescent quantum yield of 0.59 in DMF (lambdamax=509 nm). Substitution of the ancillary chloro-ligand in 1 by triphenylphosphine yields 3, which also possesses a good room-temperature luminescent quantum yield of 0.52 in DMF (lambdamax=504 nm) and a better solubility in water. Complex 3 is synthesized to demonstrate the pH dependence of luminescent properties of this C,N,Npyrazolyl cyclometalated Pt(II) system. Such a pH response is ascribable to the protonation/deprotonation of the 1-pyrazolyl-NH on the C,N,Npyrazolyl cyclometalating ligand. The pKa of the 1-pyrazolyl-NH in 3, measured in 1:2 (v/v) aqueous DMF solutions, is approximately 4.0.
Koo
Chi-Kin
CK
Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.
Ho
Yu-Man
YM
Chow
Cheuk-Fai
CF
Lam
Michael Hon-Wah
MH
Lau
Tai-Chu
TC
Wong
Wai-Yeung
WY
D018360:Crystallography, X-Ray; D003500:Cyclization; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D017671:Platinum Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011720:Pyrazoles / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012996:Solutions; D013057:Spectrum Analysis; D013696:Temperature
C520616:2-phenyl-6-(1H-pyrazol-3-yl)pyridine; D008024:Ligands; D017671:Platinum Compounds; D011720:Pyrazoles; D011725:Pyridines; D012996:Solutions