Kevlar®, Nomex®, and VAR Modification by Small Organic Molecules Anchoring: Transfusing Antibacterial Properties and Improving Water Repellency.

The surface modification of fabrics composed of Kevlar®, Nomex®, or VAR was extensively investigated. Kevlar® and Nomex® are widely-utilized aramid materials, whereas VAR is a technical fabric comprising 64% viscose, 24% para-aramid (Kevlar®), 10% polyamide, and 2% antistatic fibers. Both aramid materials and cellulose/viscose exhibit exceptional mechanical properties that render them valuable in a wide range of applications. For the herein studied modification of Kevlar®, Nomex®, and VAR, we used small organic molecules 3-allyl-5,5-dimethylhydantoin (ADMH) and 3-(acrylamidopropyl)trimethylammonium chloride (APTAC), which were anchored onto the materials under study via graft polymerization. By doing so, excellent antibacterial properties were induced in the three studied fabrics. Their water repellency was improved in most cases as well. Extensive characterization studies were conducted to probe the properties of the modified materials, employing Raman and FTIR spectroscopies, Scanning Electron Microscopy (SEM), and thermogravimetric analysis (TGA).

Graphene performs the role of an electron donor in covalently interfaced porphyrin-boron azadipyrromethene dyads and manages photoinduced charge-transfer processes.

Herein, we introduced the versatility of free-base and zinc-metallated porphyrin (H2P and ZnP, respectively) to combine with boron azadipyrromethene (azaBDP) NIR absorbing species, for extending their photophysical interest and covalently anchored onto graphene. In particular, the covalent functionalization of graphene with those H2P-azaBDP and ZnP-azaBDP dyads ensured an invariable structure, in which both chromophores and graphene are in intimate contact, free of aggregations and impurities. Both H2P-azaBDP and ZnP-azaBDP dyads were found to perform energy transfer processes between the chromophores, however, only ZnP-azaBDP confirmed additional charge separation between the chromophores yielding the ZnP˙+-azaBDP˙- charge-separated state. On the other hand, graphene in (H2P-azaBDP)-graphene and (ZnP-azaBDP)-graphene hybrids was found to act as an electron donor, yielding (H2P-azaBDP˙-)-graphene˙+ and (ZnP-azaBDP˙-)-graphene˙+ charge-separated states at an ultrafast timescale. The creation of such donor-acceptor systems, featuring graphene as an electron donor and Vis-to-NIR electron-acceptor dyads, expands their utility when considered in optoelectronic applications.

Modulation by Phosphonium Ions of the Activity of Mitotropic Agents Based on the Chemiluminescence of Luminols.

Mitochondria-targeting drugs and diagnostics are used in the monitoring and treatment of mitochondrial pathologies. In this respect, a great number of functional compounds have been made mitotropic by covalently attaching the active moiety onto a triphenylphosphonium (TPP) cation. Among these compounds, a number of molecular detectors for reactive oxygen species (ROS) are based on fluorescent and chemiluminescent probes. In this regard, luminol (probably the most widely known chemiluminescent molecule) has been employed for a number of biological applications, including ROS detection. Its oxidation under specific conditions triggers a cascade of reactions, ultimately leading to the excited 3-aminophthalate (3AP *), which emits light upon deactivation. Hence, the photophysical interaction between the light-emitting species 3AP * and TPP cations needs to be evaluated, as it can add valuable information on the design of novel emission-based mitotropic systems. We herein investigate the quenching effect of ethyltriphenylphosphonium cation onto substituted 3-aminophthalates. These were prepared in situ upon hydrolysis of the corresponding anhydrides, which were synthesized from 3-aminophthalimides. Steady-state fluorescence and time-resolved experiments were employed for the evaluation of a possible electron transfer quenching by phosphonium ions. Our experimental results confirmed such quenching, suggesting it is mainly dynamic in nature. A minor contribution of static quenching that was also detected is attributed to complex formation in the ground state. Accordingly, the chemiluminescence of luminol was indeed strongly reduced in the presence of phosphonium ions. Our results have to be taken into account during the design of new chemiluminescent mitotropic drugs or diagnostic agents of the luminol family.

Building a Functionalizable, Potent Chemiluminescent Agent: A Rational Design Study on 6,8-Substituted Luminol Derivatives.

Luminol is a prominent chemiluminescent (CL) agent, finding applications across numerous fields, including forensics, immunoassays, and imaging. Different substitution patterns on the aromatic ring can enhance or decrease its CL efficiency. We herein report a systematic study on the synthesis and photophysics of all possible 6,8-disubstituted luminol derivatives bearing H, Ph, and/or Me substituents. Their CL responses are monitored at three pH values (8, 10, and 12), thus revealing the architecture with the optimum CL efficiency. The most efficient pattern is used for the synthesis of a strongly CL luminol derivative, bearing a functional group for further, straightforward derivatization. This adduct exhibits an unprecedented increase in chemiluminescence efficiency at pH = 12, pH = 10, and especially at pH = 8 (closer to the biologically relevant conditions) compared to luminol. Complementary work on the fluorescence of the emissive species as well as quantum chemistry computations are employed for the rationalization of the observed results.

High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence.

Blue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light-emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency (EQE) of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m-2. Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures.

Oxygen- and pH-Dependent Photophysics of Fluorinated Fluorescein Derivatives: Non-Symmetrical vs. Symmetrical Fluorination.

Fluorescein, and derivatives of fluorescein, are often used as fluorescent probes and sensors. In systems where pH is a variable, protonation/deprotonation of the molecule can influence the pertinent photophysics. Fluorination of the xanthene moiety can alter the molecule's pKa such as to render a probe whose photophysics remains invariant over a wide pH range. Di-fluorination is often sufficient to accomplish this goal, as has been demonstrated with compounds such as Oregon Green in which the xanthene moiety is symmetrically difluorinated. In this work, we synthesized a non-symmetrical difluorinated analog of Oregon Green which we call Athens Green. We ascertained that the photophysics and photochemistry of Athens Green, including the oxygen-dependent photophysics that results in the sensitized production of singlet oxygen, O2(a1Δg), can differ appreciably from the photophysics of Oregon Green. Our data indicate that Athens Green will be a more benign fluorescent probe in systems that involve the production and removal of O2(a1Δg). These results expand the available options in the toolbox of fluorescein-based fluorophores.

Preparation, Photophysical and Electrochemical Evaluation of an Azaborondipyrromethene/Zinc Porphyrin/Graphene Supramolecular Nanoensemble.

The preparation of an entirely supramolecular, multichromophoric azaborondipyrromethene (ABDP)/zinc tetraphenylporphyrin (ZnTPP)/exfoliated graphene (GR) nanoensemble was accomplished. The ABDP derivative bears glycol chains for enhancing solubility and a pyridine functionality for allowing coordination with ZnTPP. The ABDP/ZnTPP/GR nanoensemble was characterized in terms of morphology and composition by using complementary microscopy imaging, thermogravimetric analysis, Raman as well as steady-state and time-resolved absorption and emission spectroscopy. The photophysical and electrochemical assessment of ABDP/ZnTPP/GR as well as the binding properties of the ABDP/ZnTPP complex, employed as a reference, are presented. Energy and electron transfer events were observed in ABDP/ZnTPP upon photoexcitation. However, in the case of ABDP/ZnTPP/GR, the graphene-induced aggregation of the chromophores alters their electronic interactions, enhancing the energy/electron transfer process between them.

Synthesis and Chemiluminescent Properties of Amino-Acylated luminol Derivatives Bearing Phosphonium Cations.

The monitoring of reactive oxygen species in living cells provides valuable information on cell function and performance. Lately, the development of chemiluminescence-based reactive oxygen species monitoring has gained increased attention due to the advantages posed by chemiluminescence, including its rapid measurement and high sensitivity. In this respect, specific organelle-targeting trackers with strong chemiluminescence performance are of high importance. We herein report the synthesis and chemiluminescence properties of eight novel phosphonium-functionalized amino-acylated luminol and isoluminol derivatives, designed as mitochondriotropic chemiluminescence reactive oxygen species trackers. Three different phosphonium cationic moieties were employed (phenyl, p-tolyl, and cyclohexyl), as well as two alkanoyl chains (hexanoyl and undecanoyl) as bridges/linkers. Synthesis is accomplished via the acylation of the corresponding phthalimides, as phthalhydrazide precursors, followed by hydrazinolysis. This method was chosen because the direct acylation of (iso)luminol was discouraging. The new derivatives' chemiluminescence was evaluated and compared with that of the parent molecules. A relatively poor chemiluminescence performance was observed for all derivatives, with the isoluminol-based ones being the poorest. This result is mainly attributed to the low yield of the fluorescence species formation during the chemiluminescence oxidation reaction.

Interfacing tetrapyridyl-C60 with porphyrin dimers via π-conjugated bridges: artificial photosynthetic systems with ultrafast charge separation.

We report on the synthesis, characterization and photophysical properties of a donor-bridge-acceptor supramolecular hybrid system, consisting of a tetrapyridyl fullerene derivative (C60-tpyr) as electron acceptor, with the four pyridyl groups as part of oligophenyleneethynylene/phenylenevinylene bridges, and zinc porphyrin dimers (ZnP)2 as electron donor species. Based on the metal-to-ligand coordination between the zinc metal centers of (ZnP)2 and the four pyridyl entities of C60-tpyr, a strong binding constant (5 × 105 M-1) for the formation of C60-tpyr·[(ZnP)2]2 was evidenced. Insights into the electronic interactions between the photoactive (ZnP)2 units and C60-tpyr emanated from complementary physicochemical assays, which were further supported by theoretical calculations. Notably, the absorption and emission titration assays revealed strong interactions between the electron donor and acceptor species within C60-tpyr·[(ZnP)2]2, both in the ground and excited state. Moreover, femtosecond and nanosecond laser photolysis transient absorption measurements were performed and provided solid evidence for intramolecular electron transfer processes derived from the singlet excited state of (ZnP)2 to C60-tpyr. Comparison with systems in which either four monomeric zinc porphyrins (ZnP) were complexed with C60-tpyr or a (ZnP)2 was coordinated with a dipyridylfullerene revealed the beneficial role of C60-tpyr in increasing the lifetime of charge-separation.

Electronic Communication between two [10]cycloparaphenylenes and Bis(azafullerene) (C59 N)2 Induced by Cooperative Complexation.

The complex of [10]cycloparaphenylene ([10]CPP) with bis(azafullerene) (C59 N)2 is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59 N)2 ⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the components especially when the second [10]CPP is bound. Unlike [10]CPP⊃C60 , in which there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon is revealed between [10]CPP and (C59 N)2 reminiscent of CPP-encapsulated metallofullerenes. Such an alternative electron-rich fullerene species demonstrates C60 -like ground-state properties and metallofullerene-like excited-state properties opening new avenues for construction of functional supramolecular architectures with organic materials.

Spectromicroscopy of C60 and azafullerene C59N: Identifying surface adsorbed water.

C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C60 and C59N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation.

Axially Substituted Silicon Phthalocyanine as Electron Donor in a Dyad and Triad with Azafullerene as Electron Acceptor for Photoinduced Charge Separation.

The synthesis of a donor-acceptor silicon phthalocyanine (SiPc)-azafullerene (C59 N) dyad 1 and of the first acceptor-donor-acceptor C59 N-SiPc-C59 N dumbbell triad 2 was accomplished. The two C59 N-based materials were comprehensively characterized with the aid of NMR spectroscopy, MALDI-MS as well as DFT calculations and their redox and photophysical properties were evaluated with CV and steady-state and time-resolved absorption and photoluminescence spectroscopy measurements. Notably, femtosecond transient absorption spectroscopy assays revealed that both dyad 1 and triad 2 undergo, after selective photoexcitation of the SiPc moiety, photoinduced electron transfer from the singlet excited state of the SiPc moiety to the azafullerene counterpart to produce the charge-separated state, with lifetimes of 660 ps, in the case of dyad 1, and 810 ps, in the case of triad 2. The current results are expected to have significant implications en route to the design of advanced C59 N-based donor-acceptor systems targeting energy conversion applications.

Azafullerene C59 in Donor-Acceptor Dyads: Synthetic Approaches and Properties.

Energy conversion schemes have attracted considerable attention in recent years. A large amount of research effort has focused on fullerenes, particularly C60 and its derivatives, as suitable electron acceptors, owing to their outstanding properties. In this context, C59 N-based donor-acceptor systems have lately attracted attention, owing to their exceptional energy-and electron-transfer properties. As a result, chemical derivatization of C59 N plays an important role in the realization of the aforementioned systems. The current Minireview aims to familiarize researchers with the main aspects of azafullerene synthesis, chemistry, and photophysical properties, while it mainly focuses on the synthetic methodologies employed for as well as on energy conversion schemes of azafullerene-based donor-acceptor systems.

Does a nitrogen matter? Synthesis and photoinduced electron transfer of perylenediimide donors covalently linked to C59N and C60 acceptors.

The first perylenediimide (PDI) covalently linked to an azafullerene (C59N) is described. PDI-C59N and PDI-C60 dyads where PDI acts as an electron-donor moiety have been synthesized by connection of the balls to the PDI 1-bay position. Photoexcitation of the PDI unit in both systems results in formation of the charge-separated state by photoinduced electron transfer from the singlet excited state of the PDI moiety to the C59N or to the C60 moiety. The charge-separated state has a lifetime of 400 ps in the case of PDI-C59N and 120 ps for the PDI-C60 dyad in benzonitrile at 298 K. This result has significant implications for the design of organic solar cells based on covalent donor-acceptor systems using C59N as an electron acceptor, indicating that longer-lived charge-separated states can be attained using C59N systems instead of C60 systems.

Tuning the reorganization energy of electron transfer in supramolecular ensembles--metalloporphyrin, oligophenylenevinylenes, and fullerene--and the impact on electron transfer kinetics.

Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 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 C60. 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.

Organic-inorganic azafullerene-gold C(59)N-Au nanohybrid: synthesis, characterization, and properties.

Azafullerene (C59 N) was functionalized using a Mannich-type reaction and then subsequently condensed with lipoic acid to yield dithiolane-modified C59 N. In the following step, the extended dithiolane moiety from the C59 N core was utilized to decorate the azafullerene sphere with gold nanoparticles (Au NPs). The latter were initially stabilized with dodecanothiol (DT⋅Au) and then integrated on azafullerene through a ligand exchange reaction with the dithiolane-functionalized C59 N to produce the C59 N/DT⋅Au nanohybrid. The nanohybrid was fully characterized by spectroscopy and microscopy, revealing the formation of spherical nanoparticles with a diameter in the range of 2-5 nm, as imaged by HR-TEM. In the electronic absorption spectrum of C59 N/DT⋅Au nanohybrid, the characteristic surface plasmon band (SPB) of Au NPs was observed, however, it was redshifted compared with that of DT⋅Au. The redshift of the SPB is indicative of closer interparticle proximity of Au NPs, in accordance with the formation of aggregated NPs as observed by TEM, in C59 N/DT⋅Au nanohybrid. Excited-state interactions in C59 N/DT⋅Au were probed by photoluminescence assays. It was found that the weak emission of C59 N at 819 nm was blueshifted by 14 nm in C59 N/DT⋅Au, but was stronger in intensity, thus suggesting energy transfer to C59 N, within the organic-inorganic C59 N/DT⋅Au nanohybrid. Finally, with the aid of pump-probe measurements and transient absorption spectroscopy, the formation of the singlet excited state of C59 N was identified.

A corrole-azafullerene dyad: synthesis, characterization, electronic interactions and photoinduced charge separation.

The preparation and characterization of the first corrole-azafullerene dyad are described. The photophysical and electrochemical properties of the new corrole-C59N dyad were examined and it was found that photoexcitation of the corrole unit leads to the formation of a charge separated state.

Azafullerene C59N-phthalocyanine dyad: synthesis, characterisation and photoinduced electron transfer.

The synthesis of a new azafullerene C(59)N-phthalocyanine (Pc) dyad is described. The key step for the synthesis of the C(59)N-Pc dyad was the formation of the C(59)N-based carboxylic acid, which was smoothly condensed with hydroxy-modified Pc. The structure of the C(59)N-Pc dyad was verified by (1)H and (13)C NMR spectroscopy, IR spectroscopy, UV/Vis spectroscopy and MS measurements. The photophysical and electrochemical properties of the C(59)N-Pc dyad were investigated in both polar and non-polar solvents by steady state and time-resolved photoluminescence and absorption spectroscopy, as well as by cyclic voltammetry. Different relaxation pathways for the photoexcited C(59)N-Pc dyad, as a result of changing the solvent polarity, were found, thus giving rise to energy-transfer phenomena in non-polar toluene and charge-transfer processes in polar benzonitrile. Finally, the detailed quenching mechanisms were evaluated and compared with that of a C(60)-Pc dyad, which revealed that the different excited-state energies and reduction potentials of the two fullerene spheres (i.e. C(59)N vs. C(60)) strongly diverged in the deactivation pathways of the excited states of the corresponding phthalocyanine dyads.

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.

Host-guest interactions in azafullerene (C59N)-single-wall carbon nanotube (SWCNT) peapod hybrid structures.

The effect of azafullerene encapsulation on the electronic states of single-wall carbon nanotubes (SWCNTs) is investigated; UV-vis-NIR absorption and photoluminescence spectroscopy shows that the interaction between SWCNTs and the encapsulated azafullerenes is originated from the weak intermolecular forces, which suggests a lack of strong doping effect such as electron transfer between them.