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

Abstract

A series of photoactive dyads bearing pyrene and metal (M Ru II ) or Os II ) tris(2,2'-bipyridine) terminals bridged by an ethynylene or Pt II bis(sacetylide) moiety has been synthesized and investigated by transient spectroscopy. Selective excitation into the terminal metal complex is possible in each case and generates the lowest energy, excited triplet state localized on that molecular fragment. For both Os II -based dyads, the triplet state is unperturbed by the appended pyrene unit and the observed photophysical properties can be understood within the framework of the energy-gap law. The triplet state localized on the metal complex in the two Ru II -based dyads is involved in reversible energy transfer with the triplet associated with the pyrene unit, which is situated at slightly lower energy. When the terminal metal complex is a Ru II bis(2,2':6',2''-terpyridyl) fragment, however, the triplet levels are inverted such that the pyrene-like triplet state lies slightly above that of the metal complex. Kinetic spectrophotometry has allowed determination of the various rate constants and energy gaps and, on the basis of nonadiabatic electron-transfer theory, it appears that the central Pt bis(sacetylide) unit is a much inferior electronic conductor than is a simple ethynylene group. Reversible energy transfer of this type greatly prolongs the triplet lifetime of the Ru II tris(2,2'-bipyridyl) fragment. For example, equilibration between the triplet states is achieved within 10 ps for the ethynylenebridged dyad while the equilibrium mixture decays with a lifetime of about 40 ms in deoxygenated acetonitrile at room temperature.

Synthesis and Spectroscopic Properties of Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes

“…Ru(bipy) 3 2ϩ dyads with either one 1-pyrenyl moiety at the 4-position of one bipy [61] or with one 1-ethynylpyrenyl moiety at the 5-position of a bipy have been investigated in detail. [62] To contribute to this field we additionally applied our coupling method to the synthesis of 5-(pyren-1-yl)-2,2Ј-bipyridine (5o) (Scheme 1 and Table 1), the subsequent complexation of which with rac- Figure 1. Structure and ORTEP [64] plot of the Λ-enantiomer of 19…”

“…[61,62] Some of these complexes show outstanding photophysical properties such as reverse triplet-triplet energy-transfer between the two partners. Ru(bipy) 3 2ϩ dyads with either one 1-pyrenyl moiety at the 4-position of one bipy [61] or with one 1-ethynylpyrenyl moiety at the 5-position of a bipy have been investigated in detail.…”

A study of acridine and acridinium-substituted bis(terpyridine)zinc(ii) and ruthenium(ii) complexes as photosensitizers for O2 (1Δg) generation

“…43b For O 2 ( 1 Δ g ) sensitization purposes the localization of the triplet state is of course less important than overall light absorption, yield of triplet formation and triplet lifetime itself, and consequently the O 2 ( 1 Δ g ) quantum yield (Φ Δ ) was evaluated. 43b One might ask why not more of the promising -multichromophoric or otherwise improved -bis(terpyridine) systems have been analyzed for their suitability as 3 47,48 In part the apparent absence of such reports can be attributed to the popular choice of anthracene 42a and pyrene 49,50 dye in multichromophore approaches because of their suitable matching triplet levels. An early seminal work on anthracenesubstituted terpyridine ligands by Maestri et al 51 mentioned O 2 ( 1 Δ g ) generation for a homoleptic bis(terpyridine) complex of Ru II , which in turn degraded the anthracene moiety due to endo-peroxide formation.…”

Carbon nanotubes dispersed in aqueous solution by ruthenium(ii) polypyridyl complexes

“…Interestingly, its emission lifetime in water reaches 665 µs. In accordance with previous studies, this phenomenon is attributed to the emission from 3 [33][34][35][36] To study the interaction of RuPy complexes with a variety of nanotubes types (chiralities) we employed HiPco nanotubes. SWCNTs were dispersed in D 2 O solutions of either RuPy1 or RuPy2 with different initial amounts of HiPco SWCNTs.…”