Singlet Excitation Energy Harvesting and Triplet Emission in the Self‐Assembled System Poly{1,4‐phenylene‐[9,9‐bis (4‐phenoxy‐butylsulfonate)]fluorene‐2,7‐diyl} copolymer/tris(bipyridyl)ruthenium(II)in Aqueous Solution

Abstract

Electronic energy transfer in conjugated polymers is of both theoretical and practical importance. At the theoretical level, the study of on-chain and interchain energy transfer is helping reveal the mechanism of exciton migration in conjugated polymers, [1] which is of fundamental importance for their application in many optoelectronic devices. Interest at the practical level extends from color tuning in light-emitting devices [2] to applications in chemical and biological sensors. [3,4] Fluorene-based copolymers are particularly attractive as energy donors in Förster Resonance Energy Transfer (FRET), because their high fluorescence quantum yields and blue emission allow efficient transfer to acceptors, emitting over the whole visible and near-infrared spectrum.[5] In addition, using complexes containing heavy metals, such as Ir, Pt, or Ru, it is possible to capture both singletand triplet-state energy, and produce high efficiency electrophosphorescent devices.[6] Whilst triplet-energy transfer to metal complexes normally involves the short-range Dexter (exchange) mechanism, [7] it is anticipated that the efficiency of this process can be optimized if both this and the long-range Förster(dipoledipole) [8] mechanisms are involved. Conjugated polyelectrolytes (CPE), conjugated polymers containing charged groups, are of particular interest, and are finding applications which include chemical and biological sensors, [3,4] light-emitting devices, [9] charge injection, and transport layers.[10] In addition, they self-assemble with oppositely charged species, such as surfactants, to build up complex multilayered structures, which have interesting materials properties with potential for molecular-electronics applications.[11] These tend to cluster in aqueous solutions, [12c] but we have shown that with the fluorene-based anionic poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP), the clusters can be broken up by addition of nonionic surfactants, such as pentaethylene glycol monododecyl ether (C 12 E 5 ), to form cylindrical micelles, in which the CPE is present as isolated chains. [12a,b,d] Polypyridylruthenium(II) complexes are amongst the most widely studied systems in inorganic photochemistry, [13] and are used in areas such as photovoltaic devices [14] and optical sensors, [15] in addition to showing potential as light-emitting electrochemical cells and other devices.[16] The emission spectrum of PBS-PFP has a near-perfect overlap with the lowest singlet-singlet transition in the absorption spectrum of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy) 3 2þ ). In addition, intersystem crossing in this metal complex to the emitting 3 MLCT (metal-toligand charge transfer) state occurs on a sub-picosecond time scale, [17] such that all electronic energy from excited singlet or triplet states of donor or acceptor will be funneled to the triplet state of the metal complex. Phase segregation is a problem in many systems involving conjugated polymers and metal complexes. However, it is ant...

Amplified Spontaneous Emission in Pentathienoacene Dioxides by Direct Optical Pump and by Energy Transfer: Correlation with Photophysical Parameters

“…This strongly suggests the presence of ground‐state interaction between 1 and 2 and between 1 and 3 . A similar behavior has been previously found with the system consisting of the organic conjugated poly{1,4‐phenylene‐[9,9‐bis(4‐phenoxy‐butylsulfonate)]fluorene‐2,7‐diyl} copolymer and the quencher tris(bipyridyl)ruthenium(II) . These high k q values are in line with the quantum chemical calculations presented in section 3.2 in three main concerns: i) Simulations anticipate the formation of robust dimers due to the suitable coupling between the ground state dipoles, either in 1 + 2 and in 1 + 3 ; ii) The relative orientation of the dipoles in each subunit is very adequate for energy transfer since the transmission of the excitation from 1 to 2 / 3 might give rise to large variations of the transition dipole‐dipole momenta; iii) In addition, we have calculated the absorption and emission spectra of 1 and compare them with the theoretical absorption profiles of 2 and 3 such as shown in Figure .…”

Incorporation of polyfluorenes into poly(lactic acid) films for sensor and optoelectronics applications

“…7(C)). This is in agreement with excitation energy being transferred from the polyelectrolyte to the ruthenium(II) complex 5. The fluorescence of the PBS‐PFP in the 400–480 nm region is attenuated in relation to that of the polymer alone, giving two apparent peaks due to substantial overlap of the polymer emission and the Ru(bpy)$_{3}^{2+}$ absorption spectra.…”

“…Conjugated polyelectrolytes (CPEs) are emerging as an important and versatile class of materials, which show excellent characteristics as optical sensors for a range of chemical and biological systems 1–3. Fluorene‐based systems are extremely good candidates for many of these applications because of high fluorescence quantum yields and blue emission4 and the possibility of tuning their emission via excitation energy transfer to long‐wavelength emitters, such as polypyridylruthenium(II) complexes 5. These complexes are used in many areas such as photovoltaic devices6 and optical sensors 7.…”

“…These complexes are used in many areas such as photovoltaic devices6 and optical sensors 7. Burrows et al 5 have shown that the usual phase separation in this system, involving conjugated polymers and metal complexes, can be minimized by the association of the opposite charges to produce self‐assembled structures.…”

Solubilization of Poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} in Water by Nonionic Amphiphiles

“…63 We have been interested in developing systems involving conjugated polyelectrolytes selfassembled with oppositely charged metal complexes for light harvesting, and have found with PBS-PFP and tris(bipyridyl) ruthenium(II) that C 12 E 5 appears to inhibit aggregation of the CPE chains by this cationic metal complex. 64 This may be associated, at least in part, to the formation of a protective sheath of surfactant molecules around the CPE backbone. This behavior shows similarities to cyclodextrin-threaded conjugated systems which have been suggested to have potential as isolated molecular wires.…”