The attachment of redox or photoactive molecules to solid surfaces is important for the development of many applications. One area of research that is receiving extensive interest at present is the immobilization of molecular dyes on mesoporous nanocrystalline metal oxide electrodes. Such functionalized films are currently under investigation for device applications ranging from solar cells to chemical and biological sensors. [1][2][3][4][5][6] Recently there has been interest in the use of more complex supramolecular or multifunctional sensitizers to build a range of new applications including heterosupramolecular devices. [7][8][9][10][11][12][13][14] The use of such materials is particularly attractive as it enables the development of electroactive structures that exhibit a remarkable degree of structural organization, improved stability, redox reversibility, and a greater functional diversity. [14][15][16] A key requirement for the exploitation of such materials in electronic devices is the ability to electrically interface the supramolecular or multifunctional materials to the metal oxide electrode whilst achieving control over key device parameters such as interfacial charge transfer. Such issues have been considered in great detail for molecular-based adsorbates, [17] but are yet to be addressed systematically for functionalized films that comprise more complex, supramolecular or multifunctional sensitizer dyes. This understanding is both of fundamental interest and essential to the design and application of such materials in electronic devices. Herein we address this issue by exploring a class of multifunctional sensitizer dyes that exhibit multistep charge-transfer cascades. We show that by careful design of the "supersensitizer" dye it is possible to modulate the charge-recombination dynamics by five orders of magnitude and achieve remarkably long-lived photoinduced charge separation at a dye/TiO 2 interface. These studies enable us to address the relationship between supermolecular dye structure and interfacial charge transfer and provide an insight into the fundamental processes that govern charge-transfer dynamics at the supermolecular sensitizer dye/TiO 2 interface.We have used sensitizer dyes in which the dye chromophore is modified by the covalent attachment of secondary electron donors. By introducing such secondary electrontransfer cascades within the dye structure, as illustrated in Figure 1, it is possible to retard the charge-recombination dynamics by increasing the physical separation between the dye-cation moiety and the surface of the TiO 2 surface. Such an approach has been recently adopted, however in all cases reported to date, only simple monomeric electron-donor groups have been employed. [9,14,18] Herein we consider the influence of structure of the electron-donating moiety upon the charge-recombination dynamics. In particular we address the influence of extended p-conjugation within the electrontransfer cascade and the use of polymeric electron-donating units which allows us to addr...

The synthesis, characterization, and properties of a highly soluble bifunctional polymer are described in which a tris(bipyridyl)Ru(II) unit acts as dye and triphenylamine units act as charge transport moieties. First a macroligand, a bipyridine carrying two poly(4-bromostyrene) chains, was synthesized by atom transfer radical polymerization (ATRP) of 4-bromostyrene in bulk using CuCl/ PMDETA as the catalytic system and bis(chloromethyl) bipyridine as the initiator. The target polymer was then obtained via a polymer amination reaction in which the bromophenyl group was converted into a triphenylamine followed by metallation of the bipyridine unit of the macroligand with Ru(II) bis(bipyridine). The reaction conditions of ATRP and polymer amination reaction were optimized, and the degree of conversion for both steps was determined by gas chromatography (GC) analysis of rest monomer content and elemental analysis of unreacted bromine, respectively. The control in molecular weight was achieved maintaining a narrow distribution in the desired low molecular weight range of bulk polymerization of 4-bromostyrene. The polymer amination reaction using the Pd(OAc) 2 and P(t-Bu)3 system was found to be very efficient, and the reaction was complete within 2 h. The metallation reaction could be followed by UV/vis spectroscopy. MALDI-TOF MS of the three polymers was carried out to obtain absolute molecular weights and their distribution. A comparison of these molecular weights gave additional information about the degree of polymer amination and metallation reaction. The thermal properties of the different polymers suggest that the thermal stability as well as the glass transition temperature increases from the starting macroligand which carries poly(4-bromostyrene) chains to the intermediate polymer having poly(vinyltriphenylamine) chains and finally to the bifunctional Ru(II) polymer complex.

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The attachment of redox or photoactive molecules to solid surfaces is important for the development of many applications. One area of research that is receiving extensive interest at present is the immobilization of molecular dyes on mesoporous nanocrystalline metal oxide electrodes. Such functionalized films are currently under investigation for device applications ranging from solar cells to chemical and biological sensors. [1][2][3][4][5][6] Recently there has been interest in the use of more complex supramolecular or multifunctional sensitizers to build a range of new applications including heterosupramolecular devices. [7][8][9][10][11][12][13][14] The use of such materials is particularly attractive as it enables the development of electroactive structures that exhibit a remarkable degree of structural organization, improved stability, redox reversibility, and a greater functional diversity. [14][15][16] A key requirement for the exploitation of such materials in electronic devices is the ability to electrically interface the supramolecular or multifunctional materials to the metal oxide electrode whilst achieving control over key device parameters such as interfacial charge transfer. Such issues have been considered in great detail for molecular-based adsorbates, [17] but are yet to be addressed systematically for functionalized films that comprise more complex, supramolecular or multifunctional sensitizer dyes. This understanding is both of fundamental interest and essential to the design and application of such materials in electronic devices. Herein we address this issue by exploring a class of multifunctional sensitizer dyes that exhibit multistep charge-transfer cascades. We show that by careful design of the "supersensitizer" dye it is possible to modulate the charge-recombination dynamics by five orders of magnitude and achieve remarkably long-lived photoinduced charge separation at a dye/TiO 2 interface. These studies enable us to address the relationship between supermolecular dye structure and interfacial charge transfer and provide an insight into the fundamental processes that govern charge-transfer dynamics at the supermolecular sensitizer dye/TiO 2 interface.We have used sensitizer dyes in which the dye chromophore is modified by the covalent attachment of secondary electron donors. By introducing such secondary electrontransfer cascades within the dye structure, as illustrated in Figure 1, it is possible to retard the charge-recombination dynamics by increasing the physical separation between the dye-cation moiety and the surface of the TiO 2 surface. Such an approach has been recently adopted, however in all cases reported to date, only simple monomeric electron-donor groups have been employed. [9,14,18] Herein we consider the influence of structure of the electron-donating moiety upon the charge-recombination dynamics. In particular we address the influence of extended p-conjugation within the electrontransfer cascade and the use of polymeric electron-donating units which allows us to addr...

No abstract