Luminescent Ruthenium Polypyridyl Complexes Containing Pendant Pyridinium Acceptors

Abstract

Direct attachment of putative electron acceptors ((bi)pyridinium ions) to either Ru(bpy)3 2+ or Ru(1,10-phenanthroline)3 2+ (excellent photo-excited-state electron donors) leads to enhancement of excited-state lifetimes, rather than the diminution anticipated from electron transfer quenching. An evaluation of photo redox and emission energetics suggests that charged “quencher” attachment lengthens luminescence lifetimes by (a) diminishing the reductant strength of the photo excited state, (b) inhibiting intersystem crossing to a short-lived d−d state, and/or (c) diminishing Franck−Condon factors for nonradiative decay.

Photoinduced Processes within Compact Dyads Based on Triphenylpyridinium‐Functionalized Bipyridyl Complexes of Ruthenium(II)

“…[10b] As expected, the value of q 1 , 868, sharply differs from that determined for 1-phen [20] of 288 (X-ray crystallography). Other relevant dihedral angles about the pyridinium ring are given in Table 1.…”

“…The only parameter to be varied is then the actual degree of electronic conjugation of A with P. In this context, the photophysical properties of the 0-bpy-2-bpy series of complexes are compared with those of an affiliated species (1-phen) previously described by Hupp and co-workers. [20] Indeed, in 1-phen, the p-phenyl-pyridinium A group (PhPy + ; Figure 1) is not sterically hindered, thus allowing the acceptor A and the phen ligand (partaking in the [Ru(phen) 3 ] 2 + P unit) to lie in a coplanar conformation (q 1 !08). 1-phen was shown to exhibit unforeseen improved luminescence while 1-bpy is almost non-luminescent.…”

“…Regarding the thermodynamics of 1-bpy, 2-bpy and 1-phen, comparison of ground-state redox potentials of their pyridinium group with corresponding excited-state reductant strength of *P shows that the formation of the CS state is for the whole three an endoergonic process by about + 0.08, + 0.35 and + 0.02 eV, [20] respectively (Figure 8). Although E-(III/II*) values are roughly estimated, [15,20,34] the perturbation of *P within 2-bpy is so large that a CS formation is merely not expected to occur.…”

“…Although E-(III/II*) values are roughly estimated, [15,20,34] the perturbation of *P within 2-bpy is so large that a CS formation is merely not expected to occur. For 1-bpy and 1-phen, [20] the very slightly unfavorable energetics can be weathered. [38] Hence, the luminescence quenching of *P within 1-bpy can be assigned to an intramolecular PET (Figure 8) all the more since:…”

Molecular Materials and Devices: Developing New Functional Systems Based on the Coordination Chemistry Approach

“…According to the calculations, the electronic band at 575 nm arises from the excitation from MO 155 (HOMO), mainly localized on the [Ru II (bipy) 2 59 This type of behavior has been ascribed to efficient mechanisms of deactivation of the 3 MLCT excited state, associated with the existence of low energy ligand field states. 49,60 The excitation process corresponds to:…”