Intramolecular Electronic Energy Transfer in Ruthenium(II) Diimine Donor/Pyrene Acceptor Complexes Linked by a Single C−C Bond

Abstract

The photophysical behavior of [(bpy) 2 Ru(L)] 2+ complexes (L ) 4-(1′′-pyrenyl)-2,2′-bipyridine, bpy-pyr; 2-(1′-pyrenyl)-1,10-phenanthroline, phen-pyr; and 2-(2′-naphthyl)-1,10-phenanthroline, phen-nap) was investigated in solutions and frozen matrices. The conformation of the linked pyrene differs in the two complexes: The pyrene moiety is conformationally constrained to be nearly perpendicular to the phenanthroline in the phen-pyr complex while the pyrene in the bpy-pyr complex has much greater flexibility about the C-C bond linking the ligand and the pyrene. The 3 MLCT excited state of the Ru(II) diimine complex and the 3 (π f π*) state of the pyrenyl substituent are nearly isoenergetic; the 3 MLCT state is the lowest energy state in the bpy-pyr complex, and the pyrene 3 (π f π*) state is lower in energy for the phen-pyr complex. The bpy-pyr complex is unique in that the 3 MLCT state has a very long lived luminescence (approximately 50 µs in degassed CH 3 CN). Luminescence decays for both pyrene containing complexes can be fit as double exponentials, indicating that the 3 MLCT and 3 (π f π*) states are not in equilibrium. Analysis of decays obtained at several temperatures reveal that energy transfer is slower than relaxation of the 3 MLCT state but more rapid than decay of the pyrene localized 3 (π f π*) state. The results also suggest that electronic coupling between the two states is weak despite the fact that the two chromophores are separated by a single covalent bond.

Long Range Electron Transfer Quenching in Polyamine Chains Bearing a Terminal Naphthalene Unit

“…[9][10][11] In particular, we have observed from NMR studies, taken with the compounds here reported and also with similar systems, containing anthracene (or benzene) as the emissive chromophore instead of naphthalene, that the first proton release always takes place with the central nitrogens. [8][9][10][11] On the other hand, the protonation sequence is mainly ruled by the existence of a minimum of repulsion between equally charged species. The obtained exponential dependence for the quenching rate constant, shown in Figure 2, is of general formula, k q ) k q (0) exp(-d), leading to a factor of 0.45 Å -1 , 1-7 suggesting that electron transfer would occur at longer distances than expected for an aliphatic system.…”

“…[5][6][7] In previous work, carried out in systems containing a polyamine chain bearing a terminal aromatic fluorophore, we have shown that the most intense emission occurs for the fully protonated form and that proton abstraction from the polyaminic chain leads to a decrease in the emission intensity. [8][9][10][11] This quenching effect is due to the intramolecular electron transfer process involving the lone pair of a deprotonated amine and the excited fluorophore. Moreover, it was also observed that the degree of quenching shows a crucial dependence, not only with the chain length but also with the stage of protonation.…”

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

“…As a matter of facts, electron transfer/transport processes are not sensitive enough to this type of parameter, [17e, 18b, 18c, 19a] contrary to luminescence [52] under proper conditions mentioned above. [64] A possible application of such switching effects could be for an optical information storage at the molecular level based on the luminescence of *P. [65] Also, the derived possibility of a conformational tuning of nonlinear two-photon absorption processes [66] that could be use for molecule-based photonic materials should be investigated inasmuch the type of compounds studied are also known to exhibit NLO properties. [67,68] …”

Intramolecular Triplet Energy Transfer in Pyrene-Metal Polypyridine Dyads: A Strategy for Extending the Triplet Lifetime of the Metal Complex

“…[5] In fact, several studies have described triplet energy transfer from a metal complex to an aryl hydrocarbon, [6±11] but in several cases the photosystems are unstable with respect to sensitized oxygenation of the polycycle. [6,7,9] Very recently, Schmehl and co-workers [12] studied the photophysical properties of ruthenium(ii) tris(diimine) complexes linked by a single bond to naphthalene or pyrene. It was concluded that the closely spaced terminals remained in weak electronic communication and that triplet states associated with these terminals were not in equilibrium at room temperature.…”