Wen Liang Huang

Synthesis, photophysical and electrochemical studies of di-2-pyridyl ketone complexes of rhodium(III)

Complexes of rhodium(III) with di-2-pyridyl ketone (dpk), Rh(dpk)(MeCN)Cl3(1) and cis-[Rh(dpk)2Cl2]+(2), have been successfully prepared and characterized. At low temperature (77 K), complex (2) in EtOH/MeOH (4:1, v/v) shows a broad, symmetric and structureless red emission with a microsecond lifetime and, hence, is assigned as the dd* phosphorescence. Electrochemical data, including cyclic voltammetry, normal pulse voltammetry, triple pulse voltammetry and controlled potential electrolysis, have been obtained for the two dpk complexes of rhodium(III) in MeCN. On the basis of analysis of the electrochemical (1,2) and luminescence data (2), electron transfer mechanisms are proposed. For complex (1), two reduction processes occur at the metal-localized orbitals with elimination of chlorides during the first reduction step. This is followed by a one-electron reduction at the metal. For complex (2), three electrons are transferred to the metal in two successive reduction steps accompanied by elimination of two chlorides. After these two reduction steps another one-electron reduction occurs at the dpk ligand.

Emission studies of hetero-bischelated iridium(III)–diimine complexes

Abstract Two mixed-ligand complexes, cis -[Ir(bipy)(HDPA)Cl 2 ]Cl and cis -[Ir(phen)(HDPA)Cl 2 ]Cl (where bipy=2,2′-bipyridine, phen=1,10-phenanthroline, and HDPA=2,2′-dipyridylamine), have been synthesized and characterized. Both complexes show spin-allowed π–π* bands in the UV region. Besides, spin-allowed and spin-forbidden charge transfer bands are also observed in the vicinity of 24.8 and 19.5 kK, respectively. The magnitude of the polarization, P , in the excitation polarization spectra obtained for the two complexes indicate that both luminophores behave as linear oscillator corresponding to the symmetry lower than C 2 v of the two complexes. The emission spectra of both cis -[Ir(bipy)(HDPA)Cl 2 ] + in neutral and cis -[Ir(phen)(HDPA)Cl 2 ] + in slightly acidified EtOH–MeOH solvent (4:1 v/v) at 77 K, exhibit 3 MLCT phosphorescence at 16–22 kK with lifetimes near 18 μs and a single vibration progression of 1240 and 1300 cm −1 , respectively. The property that the emission energy becomes smaller while the polarity of solvent increases is consistent with the orbital nature of 3 MLCT state. The emission energies of both complexes are nearly constant in acidic EtOH–MeOH solvent and are 3.1–3.3 kK smaller in basic solvent than that in the neutral one. The emissions of both complexes in the basic case are assigned as 3 MLCT emission caused by the complexes of deprotonated form, cis -Ir(bipy)(DPA)Cl 2 and cis -Ir(phen)(DPA)Cl 2, with lifetimes of approximately 19 μs.

Spectral and electrochemical properties of 2-pyridyl N-methyl-2-imidazolyl ketone complex of rhodium(III)

A new complex of [Rh(pik)2Cl2]Cl (where pik is 2-pyridyl N-methyl-2-imidazolyl ketone) has been synthesized and characterized. Both the free pik and the complex show high intensity bands in the UV region, and are assigned to spin-allowed π–π* transitions. Only the complex, however, exhibits medium-intensity absorption band profile in the lower energy region. This low-energy absorption might be explained by spin-allowed CT and, perhaps, convoluted with the weak d–d* transitions. Emission spectra at low temperature (77 K) of both the free pik and the complex in EtOH/MeOH (4:1 v/v) have also been investigated. The less structure spectrum observed for free pik is confirmed as n–π* transition. On the other hand, the complex shows a broad, symmetric, and structureless red emission with microsecond lifetime and hence is assigned as d–d* phosphorescence. Voltammetric data have also been obtained for free pik and the complex. The one-electron transfer occurred at the pi-system of the CO fragment of the free pik. There were three reduction peaks observed for the complex. The first peak, including two reduction steps with elimination of two chlorides, is consistent with ECEC reaction. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in the last reduction is assigned to be the π* orbital localized at the carbonyl fragment of pik.

Synthesis and spectral properties of 2-pyridyl N-methyl-2-imidazolyl ketone complexes of iridium(III)

Abstract Complexes of iridium(III) with 2-pyridyl N -methyl-2-imidazolyl ketone (pik), K[Ir(pik)Cl 4 ] ( 1 ) and [Ir(pik)(phen)Cl 2 ] + ( 2 ), have been successfully prepared and characterized. Both complexes show high intensity bands in the UV region, and these are assigned to spin-allowed π–π* transitions. The medium-intensity absorption band profile in the lower energy region can be explained by spin-allowed CT and, perhaps, convoluted with the weaker n–π* transitions. At low temperature (77 K), complex 2 in EtOH/MeOH (4:1, v/v) shows a structural emission with a single vibrational progression of 1090 cm −1 . The luminescence lifetime measured at 474 nm ( ν max , 0–0′ band) emission is 9.7 μs and the emission energy becomes smaller while the polarity of solvent increases. Electrochemical data have also been obtained for complex 2 in MeCN. There were two reduction peaks observed for the complex and both are one-electron charge transfer process. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in each of the reduction processes is assigned to be the π* orbital localized at the carbonyl fragment of pik. On the basis of analysis of the luminescence and electrochemical data, the emission of complex 2 is assigned as 3 MLCT, with a charge transfer to the accepting pik π* orbital.