Photophysical Study of a Self-Assembled Donor–Acceptor Two-Layer Film on TiO₂

Abstract

The self-assembled monolayer (SAM) technique was employed to fabricate a two-layer donor-acceptor film on the surface of TiO2. The approach is based on using donor and acceptor compounds with anchoring groups of different lengths. The acceptor, a fullerene derivative, has a carboxyl anchor attached to the fullerene moiety via a short linker that places the fullerene close to the surface. The donor, a porphyrin derivative, is equipped with a long linker that can penetrate between the fullerenes and keep porphyrin on top of the fullerene layer. The two-layer fullerene-porphyrin structures were deposited on a mesoporous film of TiO2 nanoparticles by immersing the TiO2 film sequentially into fullerene and porphyrin solutions. Transient absorption spectroscopy studies of the samples revealed that after the selective photoexcitation of porphyrin a fast (<5 ps) intermolecular electron transfer (ET) takes place from porphyrin to the fullerene layer, which confirms the formation of the interlayer donor-acceptor interface. Furthermore, in the second step of ET the fullerene anions donate electrons to the TiO2 nanoparticles. The latter reaction is relatively slow with an average time constant of 230 ps. It involves roughly half of the primary generated charges, and the second half relaxes by the interlayer charge recombination. The resulting state with a porphyrin cation and electron in TiO2 has an extremely long lifetime and recombines with an average time constant of 23 ms.

Photoinduced Electron Transfer in CdSe/ZnS Quantum Dot–Fullerene Hybrids

“…This band is assigned to the fullerene radical anion (C − 60 ). 6,21,38,39 The only feasible pathway leading to the C − 60 radical anion is through a photoinduced electron transfer from the excited quantum dot.…”

Color Bricks: Building Highly Organized and Strongly Absorbing Multicomponent Arrays of Terpyridyl Perylenes on Metal Oxide Surfaces

“…The layers were assembled on two types of substrate: 1) quartz plates, carefully cleaned and covered on one side with a 20 nm Al 2 O 3 layer by atomic‐layer deposition (ALD); 2) glass plates with a mesoporous TiO 2 layer on one side, prepared by a doctor‐blade technique …”

“…The plates were rinsed with MilliQ water, sonicated in acetone and isopropanol (30 min in each solvent), and dried in the oven at 150 °C for 1 h. Quartz plates with an Al 2 O 3 layer (20 nm) on one side were used as received after ALD. Mesoporous TiO 2 layers (2 μm, determined by profilometer) were deposited on clean glass plates by using a standard doctor‐blade technique …”

“…The layers were assembled on two types of substrate: 1) quartz plates, carefully cleaned and covered on one side with a2 0nmA l 2 O 3 layer by atomic-layerd eposition (ALD); 2) glass plates with am esoporousT iO 2 layer on one side, prepared by ad octor-bladetechnique. [23] Self-assembled monolayers (SAMs)w ere prepared by ao nestep process, in which the reactionvessel was loaded with asolution of PMI anhydride 4, 6,o r14 in toluene/EtOH( 9:1). The metal-oxide substrate was immersed in the required solution, and the reactionv essel was heated at 80 8Co vernight.A fter washing, drying, and recording the steady-state absorption, the plate was immersed in az inc triflate (Zn(OTf) 2 )s olution.…”

Donor/Acceptor Mixed Self‐Assembled Monolayers for Realising a Multi‐Redox‐State Surface

“…[12] For this, the design of hybrid 2 systems (organic molecule/metal electrode) that can operate in a narrow bias window is crucial. Here, inspired by some recent works on mixed SAMs composed of electron-donor (D) and electron-acceptor (A) units designed to act as artificial systems for light-harvesting and energy-transfer, [13][14][15][16][17] we have prepared bi-component mixed-SAMs on gold composed of two redox-active species that can be electrochemically switched achieving a ternary memory that operates in a quite narrow voltage window. In particular, we employ ferrocene (Fc) as electron donor unit and, as electron acceptor, an anthraquinone (AQ).…”