Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C 60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C 60 . In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates.
Neutral free-base and metallo-porphyrins have been successfully used in organic light-emitting diodes (OLEDs) and solar cells. [1][2][3][4][5] This field is mainly driven by their ease of modification to enhance light-harvesting and photoluminescence (PL) properties based on an efficient energy and/or electron transfer process from moieties attached at the periphery to the porphyrin core.This feature of dyad-like porphyrins is of utmost relevance for lighting schemes, since it could open a new avenue to decouple charge transport and emission processes by only using one active compound. This is more critical in light-emitting electrochemical cells (LECs) than in OLEDs, in which the charge transport is not performed by the emitter, but by a multilayered device architecture. 6,7 In LECs, the presence of mobile ions in the active singlelayer assists the charge injection process, while the charge transport, electron-hole recombination, and emission processes occur via the emitter. 8-10 Thus, to define clear guidelines to design LEC materials that are intrinsically able to decouple charge transport and emission is a challenge in the field. 8-10As an alternative, the host-guest approach by (i) using OLED-host materials doped with ionic liquids, 11 (ii) mixtures of iTMCs, 12-14 and (iii) using ionic-based small-molecule charge transporters, 15 has been explored in LECs to date. All these approaches show the typical problem of the host-guest strategy, that is, to determine the optimum doping level and effective doping range, which are typically very low and narrow, respectively. Here, a low doping level causes an inefficient energy transfer (ET) from the host to the guest, resulting in a poor color purity and device performance, while a high concentration of the guest leads to the a strong self-quenching of its emission and a prominent phase separation in thin films. The latter are paramount in determining the overall device performance. Herein, we report on a new concept to decouple charge transport and emission in small-molecule LECs by using only one active compound mixed with an ionic electrolyte. To this end, we took advantage of our mature experience in the synthesis of BODIPYporphyrin dyads and their implementation in solar cells [16][17][18][19] to further expand their application to lighting schemes, in which the above-mentioned drawbacks of the host-guest approach are circumvented. In detail, two BODIPY-porphyrin dyads have been designed -Scheme 1. On one hand, these dyads fulfill all of the key requirements, such as (i) the energy alignment of the electronic levels between the BODIPY and the porphyrin evokes in a chargeScheme 1 Synthesis of BODIPY-porphyrin dyads 1 and 2.
Ammonium-modified MoS and WS were prepared and characterized by complementary spectroscopic, thermal, and microscopic means. The positive charges on functionalized MoS and WS, due to the presence of ammonium units, were exploited to electrostatically bring in contact an anionic porphyrin bearing a carboxylate moiety, yielding porphyrin/MoS and porphyrin/WS ensembles, 5a and 5b, respectively. Efficient photoluminescence quenching of porphyrin's emission by MoS and WS within nanoensembles 5a and 5b, in combination with time-resolved photoluminescence assays, revealed transduction of energy from the photoexcited porphyrin to MoS or WS.
In this study, a highly efficient photocatalytic H2 production system is developed by employing porphyrins as photocatalysts. Palladium and platinum tetracarboxyporphyrins (PdTCP and PtTCP) are adsorbed or coadsorbed onto TiO2 nanoparticles (NPs), which act as the electron transport medium and as a scaffold that promotes the self‐organization of the porphyrinoids. The self‐organization of PdTCP and PtTCP, forming H‐ and J‐aggregates, respectively, is the key element for H2 evolution, as in the absence of TiO2 NPs no catalytic activity is detected. Notably, J‐aggregated PtTCPs are more efficient for H2 production than H‐aggregated PdTCPs. In this approach, a single porphyrin, which self‐organizes onto TiO2 NPs, acts as the light harvester and simultaneously as the catalyst, whereas TiO2 serves as the electron transport medium. Importantly, the concurrent adsorption of PdTCP and PtTCP onto TiO2 NPs results in the most efficient catalytic system, giving a turnover number of 22,733 and 30.2 mmol(H2) g(cat)−1.
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