Multichromophores Onto Graphene: Supramolecular Non-Covalent Approaches for Efficient Light Harvesting.

The idea of attaching multiple porphyrins to graphene is explored. A charged porphyrin salt is stabilized onto exfoliated graphene by taking advantage of π-π* interactions and a second porphyrin light harvester is anchored through electrostatic interactions with the former. The interactions are capable of allowing electronic communication of the second, electrostatically attached, porphyrin with graphene, effectively quenching its emission. The graphene-porphyrin-porphyrin triad is examined through optical (UV-Vis, steady state and time resolved photoluminescence) techniques, while electrochemistry is employed to study the thermodynamically favored pathways through which the interaction occurs. The porphyrin that is electrostatically stabilized onto the graphene nanoensemble shows lifetimes one order of magnitude faster than its π-π* stacked analogue suggesting a more efficient pathwa

Chemical Functionalization of Exfoliated Graphene

Graphene is turning out to be the material that will effectively kick-start a new era for nanotechnology. The impressive properties of this atom-thick carbon layer are taking shape and form with early reports of successful applications based on it. The turning point for this material will be its low cost mass production. In this report a chemist’s perspective on the production methods for graphene and the subsequent functionalization processes is discussed

Donor-acceptor graphene-based hybrid materials for managing photoinduced electrontransfer reactions

Graphene research and in particular the topic of chemical functionalization has been exploded in the last decade. The main aim is to induce solubility and thereby enhance processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. In this frame, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets, soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. Some donor-acceptor hybrid materials with photo- and/or electro-active components were prepared and characterized, while their charge-transfer properties were evaluated. However, it was obvious that the highly defected framework of graphene oxide cannot be really utilized in applications that are governed by charge-transfer processes, for example in solar cells. The alternative route for solubilizing and modifying graphene by exfoliating graphite is the current method of choice for the realization of novel hybrid materials and further boost their direct applicability in artificial photosynthesis and the construction of photovoltaic devices. In this review article, the routes for obtaining donor-acceptor graphene-based hybrid materials for managing charge-transfer phenomena, mainly, but not exclusively, with porphyrins and phthalocyanines are presented. Earlier examples and studies performed on graphene oxide modified with organic electron donors are also given

One-step covalent hydrophobic/hydrophilic functionalization of chemically exfoliated molybdenum disulfide nanosheets with RAFT derived polymers

The covalent functionalization of chemically exfoliated molybdenum disulfide (ce-MoS2) with hydrophobic poly(methyl methacrylate) and hydrophilic poly(acrylic acid) polymers, in a single-step without additives, is presented. The nature of chemical modification and the impact on the structure of ce-MoS2 were spectroscopically investigated. Complexation of Eu3+ was accomplished on grafted polycarboxylate chains on MoS2

Graphene exfoliation in organic solvents and switching solubility in aqueous media with the aid of amphiphilic block copolymers.

The successful exfoliation of graphite to graphene sheets in liquid phase via tip sonication was achieved. A number of solvents were examined for several time periods and it was found that o-dichlorobenzene (o-DCB) and N-methyl-1,2-pyrolidone (NMP) are ideal solvents to exfoliate graphite and produce stable 10 dispersions of graphene. The exfoliated graphene dispersions were characterized by complementary techniques including AFM, DLS, TGA and Raman. Furthermore, treatment of stable dispersions of exfoliated graphene sheets in NMP with poly[styrene-b-(2-vinylpyridine)] block copolymer, under acidic conditions, resulted on aqueous solubilization of graphene. Similar results were obtained, i.e. transfer of graphene from the organic to the aqueous phase, when poly(isoprene-b-acrylic acid) block copolymer was 15 added on exfoliated graphene in NMP

Ping‐pong energy transfer in covalently linked porphyrin‐MoS2 architectures

Molybdenum disulfide nanosheets covalently modified with porphyrin were prepared and fully characterized. Neither the porphyrin absorption nor its fluorescence was notably affected by covalent linkage to MoS2. The use of transient absorption spectroscopy showed that a complex ping‐pong energy‐transfer mechanism, namely from the porphyrin to MoS2 and back to the porphyrin, operated. This study reveals the potential of transition‐metal dichalcogenides in photosensitization processes.This project has received funding from EC H2020 under the Marie Sklodowska‐Curie grant agreement No. 642742. HRSTEM and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016‐79776‐P (AEI/FEDER, UE) and from EC H2020 programs “Graphene Flagship” (785219), FLAG‐ERA—“GATES” (JTC‐PCI2018‐093137) and “ESTEEM3” (823717). R.A. also acknowledges Government of Aragon under the project “Construyendo Europa desde Aragon” 2014‐2020 (grant number E13_17R).Peer reviewe

New hybrid materials with porphyrin-ferrocene and porphyrin-pyrene covalently linked to single-walled carbon nanotubes.

Novel porphyrin derivatives bearing additional pyrene or ferrocene units as light harvesting antenna systems were synthesized and fully characterized. Following a covalent functionalization approach for single-walled carbon nanotubes (SWCNTs), stable SWCNT suspensions in common organic solvents 10 were produced. Subsequently, the resulting porphyrin-pyrene and porphyrin-ferrocene dyads were incorporated onto the nanotubes' backbone yielding donor-donor-acceptor hybrids. The resulting hybrid materials were soluble in common organic solvents and were characterized using micro-Raman, ATR-IR, UV-Vis and photoluminescence spectroscopy, transmission electron microscopy, thermogravimetric analysis and εlectrochemistry. Photoluminescence quenching of the porphyrin emission in both hybrid 15 materials was detected thus suggesting the potentiality of these materials in photoelectrochemical cells

Pyrene coating transition metal disulfides as protection from photooxidation and environmental aging

This article belongs to the Section Nanocomposite Materials.Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical properties of TMD/pyrene are assessed via electronic absorption and fluorescence emission spectroscopy. High-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy confirms extensive pyrene surface coverage, with density functional theory calculations suggesting a strongly bound stable parallel-stacked pyrene coverage of ~2–3 layers on the TMD surfaces. Raman spectroscopy of exfoliated TMDs while irradiating at 0.9 mW/4 μm2 under ambient conditions shows new and strong Raman bands due to oxidized states of Mo and W. Yet remarkably, under the same exposure conditions TMD/pyrene remain unperturbed. The current findings demonstrate that pyrene physisorbed on MoS2 and WS2 acts as an environmental barrier, preventing oxidative surface reactions in the TMDs catalyzed by moisture, air, and assisted by laser irradiation. Raman spectroscopy confirms that the hybrid materials stored under ambient conditions for two years remained structurally unaltered, corroborating the beneficial role of pyrene for not only hindering oxidation but also inhibiting aging.This research was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742, under the “Graphene Flagship” project grant agreement No 785219 and under the ESTEEM-3 project grant agreement No 823717. This research was also partially funded by the project “Advanced Materials and Devices” (MIS 5002409), which is implemented under the “Action for the Strategic Development on the Research and Technological Sector” funded by the Operational Program “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). This work was supported by the COST Action CA15107 MultiComp. This research was also supported by the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P), from the Government of Aragon and the European Social Fund under the project “Construyendo Europa desde Aragon” 2014–2020 (grant number E13_17R).Peer reviewe

Electrocatalytic activity for proton reduction by a covalent non-metal graphene-fullerene hybrid

A non-metal covalent hybrid of fullerene and graphene was synthesized in one step via fluorographene chemistry. Its electrocatalytic performance for the hydrogen evolution reaction and durability was ascribed to intrahybrid charge-transfer phenomena, exploiting the electron-accepting properties of C-60 and the high conductivity and large surface area of graphene.Web of Science58608399839

Pyrene-functionalized tungsten disulfide as stable resistive photosensor

Pyrene carrying an 1,2-dithiolane linker was employed to functionalize exfoliated WS2 and the resulting material was used in a proof-of-concept application as a photoresistor type sensor. The WS2–pyrene hybrid material was comprehensively characterized by spectroscopic, thermal and microscopy techniques, coupled to density functional theory modelling. The high solubility of the WS2–pyrene hybrid material allows easy manipulation in wet media, making it suitable for device fabrication. Thus, a two-terminal resistive photosensor was developed and tested for photodetection. The photosensitivity of WS2 was improved by the presence of covalently attached pyrene by a factor of 2–3, the response linearly dependent on light intensity. Device reaction time was also improved, and critically the photosensor stability was significantly enhanced. Functionalization of exfoliated WS2 material heals vacancies, oxidation and other damage sites liable to impede photoelectric response. This proof-of-concept study opens the way for incorporation of diverse chromophores active in the visible and/or NIR region of the electromagnetic spectrum to WS2 in order to stabilise it and broaden its photoresistive sensing applicability