Metal-to-Metal Electron-Transfer Emission in Cyanide-Bridged Chromium−Ruthenium Complexes: Effects of Configurational Mixing Between Ligand Field and Charge Transfer Excited States

Abstract

Irradiations of the transition metal-to-transition metal charge transfer (MMCT) absorption bands of a series of cyanide-bridged chromium(III)-ruthenium(II) complexes at 77 K leads to near-infrared emission spectra of the corresponding chromium(II)-ruthenium(III) electron transfer excited states. The lifetimes of most of the MMCT excited states increase more than 10-fold when their am(m)ine ligands are perdueterated. These unique emissions have weak, low frequency vibronic sidebands that correspond to the small excited-state distortions in metal-ligand bonds that are characteristic of transition metal electron transfer involving only the non-bonding metal centered d-orbitals suggesting that the excited-state Cr(II) center has a triplet spin configuration. However, most of the electronically excited complexes probably have overall doublet spin multiplicity and exhibit an excitation energy dependent dual emission with the near in energy Cr(III)-centered and MMCT doublet excited states forming an unusual mixed valence pair.

Electronic Energy Transduction from {Ru(py)4} Chromophores to Cr(III) Luminophores

“…It is important to note that the emission wavelengths of 1 4– – 3 4– in methanol under MM′CT illumination are very similar, despite different MM′CT state energies. These results allow us to rule out major contributions from MM′CT emission, which is in stark contrast to {Cr-Ru-Cr} complexes reported by Endicott and co-workers. , …”

How fast is optically induced electron transfer in organic mixed valence systems?

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In most but not all cases, asymmetric systems were in focus in which -owing either to two different redox centres or to an asymmetric bridging moiety -the two diabatic states possess different Gibbs energies. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In most but not all cases, asymmetric systems were in focus in which -owing either to two different redox centres or to an asymmetric bridging moiety -the two diabatic states possess different Gibbs energies.…”

Inversion of donor–acceptor roles in photoinduced intervalence charge transfers

“…ESMV is a more general concept, including also those systems where mixed valence interactions are already present in the ground state (GSMV). ESMV systems can result, for example, from photoexcitation on the GSIVCT band of a GSMV moiety, [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] or from photoinduced energy transfer to GSMV-donor-or GSMV-acceptor-centered excited states. 27,36,37 In contrast, the term PIMV is reserved only for those systems where GSMV interactions are absent.…”