Luminescence of Transition Metal d6 Chelates

Abstract

Emission and absorption spectra have been determined for Rh(III) and Ir(1II) complexes of the nitrogen ligands, ethylenediamine (en) pyridine, 2,2′-dipyridyl (dip), and 1,10-phenanthroline (phen). Emission lifetimes at 77°K in glassy solution and at room temperature have been measured. From lifetime measurements and the energies of emission, luminescence from these heavy metal chelates is assigned as “phosphorescence,” indicating complete intersystem crossing, consistent with the heavy metal spin–orbit mixing of excited singlet and triplet states. Spin–orbit coupling is further manifested in the appearance of room temperature phosphorescence for the bis Ir(III) complexes of dip and phen. The emission can be classified as (1) metal localized (“d–d” emission) or (2) “delocalized molecular” (ligand localized or charge transfer). The metal localized emission appears at low energies, is broad and structureless, and exhibits a large Stokes shift. The delocalized molecular emission appears at higher energies and shows characteristic vibrational structure and a small Stokes shift. The intensity of the delocalized molecular emission is large, indicating a quantum yield approaching one. The “d–d” emission is less intense. Correlation of the relative emission intensities of the “d–d” emitters with the displacement of the emitting state from the ground state determined from the Stokes shifts suggest that recent Jortner and Rice theories of nonradiative transitions rationalizes these relative intensities. The “strong coupling” limit is illustrated by the tris and bis(en) complexes of Ir(III) and is consistent with the low intensity emission of these complexes. The larger emission intensity of the Rh(III) en complexes is consistent with the weaker vibrational coupling predicted for these complexes by the theory.

Luminescence Properties of Transition-Metal Ions in Double Complex Salts

“…Some of the double complexes which we have looked at exhibit substantial overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, the emission being at higher energy than the absorption and the donor possessing a strong transition dipole moment. 6 ] an anion emission much weaker than for the component complexes [18][19][20][21] were measured. The donor components of these systems exhibit an electric dipole allowed n-n* transition giving rise to a strong dipole moment which would be very suitable for initiating energy transfer, and the acceptors in mono-complexes are known to be relatively poor emitters [22,23].…”

Synthesis and Spectral Properties of Phenyl‐Pyridin‐2‐Ylmethylene‐Amine Complex of Rhodium(III)

“…This is con sis tent with the con clusion de rived from the band-shape, life time and the peak po sition stud ies per formed on rho dium com plexes co or di nated with polypyridine lig ands. 13 The emis sion po lar iza tion spec tra of the com plex (excited by 313 and 365 nm) ex hibit flat with a van ish ing slope. This ob ser va tion in di cates that the com bi na tion of ab sorber and emit ter(s) gives the same po lar iza tion across the emission band.…”

“…The lat ter in the bipyridine (bipy) co or di nated an a logues has also been reported at about 26 kK. 13 The ex ci ta tion po lar iza tion spec trum of the com plex is shown in the bot tom half (part B) of Fig. 3.…”

“…The pro ton NMR spec trum ac quired for the com plex reveals 8 unequivalent pro tons and the 13 C spec trum ex hib its 10 car bon res o nance sig nals. Ac cord ing to these NMR data, the two PA lig ands are chem i cally equiv a lent in [Rh(PA)2Cl2] + .…”

Luminescent Eu(III) and Gd(III) Trisbipyridine Cryptates: Experimental and Theoretical Study of the Substituent Effects

“…[29] By comparison, 2,2'-bipyridine itself shows a structured phosphorescence band in a methanol-ethanol mixture (4:1, v/v) at 77 K with a high-energy feature at 425 nm, the lowest energy triplet was measured at 23 500 cm À1 for the phosphorescence spectrum in water, cyclohexane and hexane. [36,37] The triplet state level for the bipyridine chelate (2,2,2,2-[(2,2-bipyridine-6,6-diyl)bis(methylenenitrilo)] tetrakis (acetic acid) [38] was found at 22 400 cm À1 .…”