Light Harvesting and Charge Separation in a π-Conjugated Antenna Polymer Bound to TiO₂

Abstract

This paper describes photophysical and photoelectrochemical characterization of a light harvesting polychromophore array featuring a polyfluorene backbone with covalently Ru(II) polypyridyl complexes (PF-Ru-A), adsorbed on the surface of mesostructured TiO 2 (PFRu-A//TiO2). The surface adsorbed polymer is characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and attenuated total reflectanceFourier transform infrared (ATR-FTIR) spectroscopy, providing evidence for the morphology of the surface adsorbed polymer and the mode of binding. Photoexcitation of the Ru complexes bound to the metal oxide surface (proximal) results in electron injection into the conduction band of TiO 2 , which is then followed by ultrafast hole transfer to the polymer to form oxidized polyfluorene (PF + ). More interestingly, chromophores that are not directly bound to the TiO 2 interface (distal) that are excited participate in site-to-site energy transfer processes that transport the excited state to surface bound chromophores where charge injection occurs, underscoring the antenna-like nature of the polymer assembly. The charge separated state is long lived and persists for >100 µs, a consequence of the increased separation between the hole and injected electron.

Light-harvesting antennae based on photoactive silicon nanocrystals functionalized with porphyrin chromophores

“…The majority of such articial antennas are based on dendrimers. Other nanostructures have been investigated: for example, zeolites, 13 polymers, 14,15 G-quartet nanostructures, 16 and DNA. Other nanostructures have been investigated: for example, zeolites, 13 polymers, 14,15 G-quartet nanostructures, 16 and DNA.…”

Polymer‐Based Ruthenium(II) Polypyridyl Chromophores on TiO2 for Solar Energy Conversion

“…Loss of the bpy .− absorption at 385 nm while retaining the ground‐state bleach amplitude at 450 nm is the spectral signature of decay of the MLCT state by electron injection into TiO 2 . The decay at 385 nm (Figure D) is multi‐exponential, exhibiting both fast ( τ 1 =60 ps) and slow ( τ 2 =500 ps) components, as has been observed in a similar light‐harvesting array at TiO 2 featuring a poly(fluorene) polymer backbone . This photoinduced electron injection event has been shown to be a multi‐exponential process, resulting from dynamic relaxation processes that occur within the photoexcited chromophores.…”

“…We recently developed a nitroxide‐mediated living radical polymerization (NMP) method to afford polymers with controlled molecular weight and narrow PDI . Click assembly via an azide‐alkyne Huisgen cycloaddition reaction allows attachment of ethyl ester‐containing polypyridyl Ru II chromophores to each polystyrene repeat unit (PS‐Ru‐E) …”

“…In Figure B, the polymer appears to form a film that uniformly coats the surface of the nano‐TiO 2 particles. This morphology is similar to that seen in a previous study where a polyfluorene‐Ru polymer was anchored to nano‐TiO 2 via the carboxylate units on the bipyridine ligands . The evidence here suggests a similar binding motif between PF‐Ru‐A and the nano‐TiO 2 particles.…”

Light-Driven Water Oxidation Using Polyelectrolyte Layer-by-Layer Chromophore–Catalyst Assemblies

“…[1][2][3] Most photoanodes used in DSPECs utilize Ru polypyridine chromophores and a water oxidation catalyst or covalently linked chromophore-catalyst assemblies bound to mesoporous wide bandgap metal oxide semiconductor films. [4][5][6][7][8] In spite of considerable synthetic efforts directed to the construction of chromophore and catalyst assemblies, only linkers such as phosphonate and carboxylate groups, which form a covalent bond to the oxide surface (generally TiO 2 ), have been explored. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 Layer-by-layer (LbL) polyelectrolyte self-assembly involves the sequential deposition of oppositely charged polymers to build up multilayer polymer structures that feature a tailored nanostructure that can be defined by the polyelectrolyte structures and sequence used during multilayer construction.…”