Solon P. Economopoulos

Exfoliation and Chemical Modification Using Microwave Irradiation Affording Highly Functionalized Graphene

Efficient exfoliation of graphite flakes by sonicating them in benzylamine was accomplished, affording stable suspensions of few-layers graphene. The latter were chemically modified following the Bingel reaction conditions, with the aid of microwave irradiation, producing highly functionalized graphene-based hybrid materials. The resulting hybrid materials, possessing cyclopropanated malonate units covalently grafted onto the graphene skeleton, formed stable suspensions for several days in a variety of organic solvents and were characterized by diverse and complementary spectroscopic, thermal, gravimetric, and high-resolution electron microscopy techniques. When a malonate derivative, bearing the electro-active extended tetrathiafulvalene (exTTF) moiety, was synthesized and used for the functionalization of graphene, energy dispersive X-ray (EDX) analysis verified the presence of sulfur in the corresponding graphene-based hybrid material. Moreover, the redox potentials of the exTTF-graphene hybrid material were determined by electrochemistry, while the formation of a radical ion pair that includes one-electron oxidation of exTTF and one-electron reduction of graphene was suggested with the energy gap of (graphene)(•-)-(exTTF)(•+) being calculated as 1.23 eV.

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 chemists perspective on the production methods for graphene and the subsequent functionalization processes is discussed.

Photoinduced electron transfer in aqueous carbon nanotube/block copolymer/CdS hybrids: application in the construction of photoelectrochemical cells

Pristine and shorted multi-walled carbon nanotubes (pMWCNT and sMWCNT, respectively) non-covalently modified with a block copolymer (poly[sodium (2-sulfamate-3-carboxylate) isoprene-b-styrene]—abbreviated as CSI) are used for the formation of CdS semiconductor nanohybrids. The CdS nanoparticles are preferentially localized on the surface of the nanotubes due to specific interactions with the polymer chains. In these nanohybrid materials photoinduced electron transfer phenomena are found to occur from the photoexcited CdS nanoparticles to the nanotubes as evidenced by the efficient fluorescence emission quenching of CdS nanoparticles. Nanosecond transient absorption spectroscopy sheds light on the transient species formed by charge separation, namely (pMWCNT)˙−/CSI/(CdS)˙+ and (sMWCNT)˙−/CSI/(CdS)˙+. The MWCNT/CSI/CdS nanohybrid materials are deposited onto ITO electrodes by the drop-casting method. The ITO/sMWCNT/CSI/CdS electrode exhibit an incident photon to photocurrent efficiency (IPCE) of 7% at an applied bias of +0.2 V vs.SCE in a standard three-compartment electrochemical cell. Direct electron injection from the reduced nanotubes to ITO electrode after the photoinduced charge separation is responsible for the photocurrent generation.

Solvent-free microwave-assisted Bingel reaction in carbon nanohorns

In this paper we exploit the benefits of microwave-assisted functionalization of carbon nanohorns (CNHs). Using Bingel reaction conditions we have successfully incorporated malonyl moieties in CNHs. The resulting hybrid materials were characterized by diverse and complementary analytical techniques, including Raman, UV-Vis and photoluminescence spectroscopy, transmission electron microscopy, thermogravimetric analysis, while electrochemistry was employed to determine possible variations in the energy levels when photoactive units were grafted onto the skeleton of CNHs.

Novel BODIPY-based conjugated polymers donors for organic photovoltaic applications

Five new polymers based on the 4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene core (BODIPY) chromophore moiety have been synthesized as low bandgap polymers for optoelectronic applications. The polymers exhibited high solubility in common organic solvents and optical bandgaps ranging from 1.7–2 eV. The materials were characterized using NMR, UV-Vis, steady state and time-resolved photoluminescence and the energy levels were examined using electrochemistry and validated using quantum chemical calculations. Finally, a representative BODIPY derivative : PCBM blend was examined in terms of photovoltaic properties. Preliminary device performance parameters as a function of photo-active layer thickness and composition are reported and discussed, relating to power conversion efficiency values.

Microwave assisted covalent functionalization of C60@SWCNT peapods

The covalent functionalization of the external wall of C(60)@SWCNT peapods, by in situ generated aryl diazonium salts, assisted by microwave irradiation is reported. Spectroscopic, thermal and microscopy characterization was performed. Electrochemistry revealed the three reversible reductions of encapsulated C(60), however, shifted towards positive potentials when compared with those of intact C(60).

Fullerene–Coumarin Dyad as a Selective Metal Receptor: Synthesis, Photophysical Properties, Electrochemistry and Ion Binding Studies

A coumarin derivative with a malonate unit has been synthesized and used for the preparation of a fullerene-coumarin dyad through the Bingel cyclopropanation method. The newly synthesized dyad is soluble in organic solvents and has been fully characterized with traditional spectroscopic techniques. Electronic interactions between the two components of the dyad were probed with the aid of UV/Vis spectroscopy, fluorescence emission, and electrochemistry measurements. Our studies clearly show the presence of electronic interactions between C(60) and modified coumarin in the ground state; efficient electron-transfer quenching of the singlet excited state of the coumarin moiety by the appended fullerene sphere was also observed. Time-resolved fluorescence measurements revealed lifetimes for the coumarin-C(60) dyad at a maximum of 50 ps, while the quantum yield was reaching unity. Additionally, the redox potentials of the C(60)-coumarin dyad were determined and the energetics of the electron-transfer processes were evaluated. Finally, after alkaline treatment of C(60)-coumarin, which resulted in the deprotection of carboxylate units, the dyad was tested as a metal receptor for divalent metal cations; ion competition studies and fluorescence experiments showed binding selectivity for lead ions.

2-(2,3,4,5,6-Pentafluorophenyl)-1H-benzo[d]imidazole, a fluorine-rich building block for the preparation of conjugated polymer donors for organic solar cell applications

We have introduced the pentafluorophenyl substituted benzimidazole as a building block of conjugated polymers for optoelectronic applications. We present the synthesis of a copolymer bearing fluorene as the comonomer. A detailed characterization of the novel material including structural, electrochemical and optical (using absorption, emission and time-resolved photoluminescence techniques) properties as well as computational modeling is described. The polymer exhibits highly efficient photoluminescence quenching when blended with fullerene derivatives (PCBM). The experimental results are compared with the alternating fluorene copolymer (APFO-3) in order to identify structure and property relations with the novel synthesized conjugated polymer. Early photovoltaic performance data are presented and compared with the well established APFO-3 : PCBM material system.