The photophysical properties of a series of ruthenium trisbipyridine complexes covalently linked to aromatic chromophores of the type [Ru(bpy)2(4-methyl-4‘-(2-arylethyl)-2,2‘-bipyridine)]2+(ClO4)2, where aryl = 2-naphthyl ([Ru]-naphthalene), 1-pyrenyl ([Ru]-pyrene), and 9-anthryl ([Ru]-anthracene) have been investigated at room temperature and at 77 K. The photophysical properties of these bichromophores are determined by intramolecular energy-transfer processes that are governed by the relative positions of the various singlet and triplet energy levels. As a result, fluorescence from each of the pendant aromatic chromophores is completely quenched following their photoexcitation. For [Ru]-naphthalene the initial excitation energy is localized on the [Ru]-centered 3MLCT state, whereas for [Ru]-anthracene the energy is localized on the anthracene triplet state. Since the [Ru]-centered 3MLCT state and the lowest energy pyrene triplet state are isoenergetic, an equilibrium is established resulting in a long-lived room-temperature 3MLCT emission from [Ru]-pyrene (τ = 5.23 μs). At 77 K dual emission is observed from this bichromophore comprising pyrene phosphorescence and 3MLCT emission, the relative proportions of which vary with time after the laser pulse.

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The syntheses of linear and star-shaped light harvesting polymers with well defined structure and narrow molecular weight distribution are described. These polymers have ruthenium polybipyridine moieties as the energy trap cores and styrene functionalized coumarin monomers as the light absorbing antenna chromophores. The polymers have been made by reversible addition-fragmentation chain transfer (RAFT) polymerisation using di-or hexafunctional ruthenium-containing RAFT agents. The resulting ruthenium-containing polymers have narrow molecular weight distribution (polydispersity v 1.1) and exhibit energy transfer efficiencies of up to 60% between the coumarin donor dyes and the ruthenium acceptor chromophores.

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With the rapid development of nanotechnology, methodologies that will enable the cost-effective, controlled assembly of nanostructures in a routine manner are in high demand. Photoactive polymers are promising candidates to fulfill the materials requirements for energy storage and conversion devices, molecular sensors, and photonic materials. 1 Of particular interest is the utilization of efficient energy transfer processes in a polymer chain containing sequences of donor chromophores that absorb the incident light and the subsequent trapping of the energy in suitably placed acceptor species. 2 Such "antenna" polymers simulate the efficient light harvesting process of pigment arrays in the photosynthetic apparatus of green plants and can act to effectively increase the light absorption cross section of components in photomolecular devices.The synthesis of photoactive polymers with welldefined architectures has long been of great interest to photochemists but is difficult to achieve by conventional free radical polymerization methods. Living radical polymerization has made great progress in recent years and emerged as one of the most effective synthetic routes to make well-defined polymers. 3 Among them, reversible addition-fragmentation chain transfer (RAFT) polymerization appears particularly useful and, in principle, could be applied to all classical radical polymerization systems.The RAFT process involves performing a conventional free radical polymerization in the presence of certain thiocarbonylthio compounds SdC(Z)-SR that act as highly efficient reversible addition-fragmentation chain transfer agents and provide the polymerization with living characteristics. Following RAFT polymerization, nearly all polymer chains will have the thiocarbonylthio and R as end groups. RAFT polymerization thus provides a means of introducing specifically placed photoactive moieties into polymer chains using appropriately functionalized RAFT agents.We have previously incorporated chromophores into RAFT agents by the coupling reaction of 4-cyano-4-((thiobenzoyl)sulfanyl)pentanoic acid (RAFT-acid) with the required hydroxy-functionalized chromophores. 4 However, the stability of the resulting ester linkage can limit the applications in a number of circumstances, such as in the presence of acid or base. Although the ester linkage could be replaced by a more stable amide linkage, this general method is limited by the low yield of the coupling reaction between RAFT-acid and aminefunctionalized chromophores due to the competing aminolysis reaction of the thiocarbonylthio group by the amine.We describe here a novel alternative method to introduce suitable chromophores into a RAFT agent. The overall process and mechanism are outlined in Scheme 1. This procedure involves performing a RAFTlike polymerization reaction, except the molar ratio of monomer to RAFT agent is kept at unity. A small amount (1-2% molar equivalent) of free radical initiator is used to initiate the reaction. In our work 2-cyanoprop-2-yl dithiobenzoate 5 and 2,2′-az...

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The quenching (ηq) and subsequent cage-escape efficiency (ηce) have been measured for three arene-linked ruthenium trisbipyridine complexes quenched by methyl viologen (MV2+). The bichromophoric complexes are of the type [Ru(bpy)2(4-methyl-4‘-(2-arylethyl)-2,2‘-bipyridine)]2+(ClO4 -)2 where aryl = 2-naphthyl ([Ru]-naphthalene), 1-pyrenyl ([Ru]-pyrene), and 9-anthryl ([Ru]-anthracene). The overall yield of MV•+ is given by the product ηqηce, which depends both on specific solvent effects and on the nature of the quenched excited state of the bichromophore, i.e., whether it is a metal-to-ligand charge transfer (3MLCT) or aromatic triplet state. In aqueous buffer the production of MV•+ is low for the three bichromophores (<10%). In methanol and acetonitrile MV•+ yields for [Ru]-anthracene and [Ru]-pyrene are >70%, reflecting the arene triplet character of the lowest excited state. This increase is due to an increase in the cage-escape efficiency (ηce) in these solvents. In contrast, for [Ru]-naphthalene the lowest excited state is 3MLCT in character and the yield of MV•+ in acetonitrile and methanol remains <10%. NMR spectra of the linking ethane group suggest that the bichromophores adopt different conformations in the different solvents, which could lead to the observed differences in ηce.

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