Georgios Rotas

Fullerene‐based donor‐acceptor (D‐A) dyads have been extensively studied for their unique electronic properties, with applications in photoinduced energy conversion devices. In these systems, dynamic quenching of the excited donor's emission occurs, via energy or electron transfer to the fullerene acceptor. However, there are no reports on fullerene dyads bearing chemiluminescent donor analogues. In this context, the synthesis of two luminol‐fullerene D‐A dyads, bridged with alkyl chains of different lengths, is reported herein. The electronic communication between the two moieties was thoroughly evaluated, following either the photo‐ or chemi‐excitation of the linked units. Steady state and time‐resolved absorption studies, combined with emission techniques, were employed to monitor the deactivation fate of excited species. In general, a significant quenching of the excited luminol‐derived emission signals was observed, revealing detectable intramolecular interactions between the two moieties. Unlike what is usually observed in other luminol‐based D‐A systems, quenching of the excited species generated upon photo‐ and chemi‐excitation of the luminol‐fullerene dyads is attributed to electron rather than energy transfer. This was found to be consistent with the estimated Gibbs energy of photoinduced electron transfer and with DFT theoretical calculations.

Aggregation-induced emission dyes (AIEs) have gained significant interest due to their unique optical properties. Upon aggregation, AIEs can exhibit remarkable fluorescence enhancement. These systems are ideal candidates for applications in bioimaging, such as image-guided drug delivery or surgery. Encapsulation of AIEs in polymeric nanocarriers can result in biocompatible and efficient nanosystems. Herein, we report the fabrication of novel nanoaggregates formulated by amino terpolymer and tetraphenylethylene (TPE) AIE in aqueous media. Poly(di(ethylene glycol) methyl ether methacrylate-co-2-(dimethylamino)ethylmethacrylate-co-oligoethylene glycol methyl ether methacrylate), P(DEGMA-co-DMAEMA-co-OEGMA) hydrophilic terpolymer was utilized for the complexation of the sodium tetraphenylethylene 4,4′,4″,4‴-tetrasulfonate AIE dye. Fluorescence spectroscopy, physicochemical studies, and self-assembly in aqueous and fetal bovine serum media were carried out. The finely dispersed nanoparticles exhibited enhanced fluorescence compared to the pure dye. To investigate the role of tertiary amino groups in the aggregation phenomenon, the polymer was quaternized, and quaternized polymer nanocarriers were fabricated. The increase in fluorescence intensity indicated stronger interaction between the cationic polymer analog and the dye. A stronger interaction between the nanoparticles and fetal bovine serum was observed in the case of the quaternized polymer. Thus, P(DEGMA-co-DMAEMA-co-OEGMA) formulations are better candidates for bioimaging applications than the quaternized ones, presenting both aggregation-induced emission and less interaction with fetal bovine serum.

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).

Solution-processable molecular dopants are popular wet-lab mediators to engineer the electronic properties of organic semiconductors and to optimize the level performance of their corresponding devices. Nonetheless, the exact doping mechanism that is operative during the interaction of organic semiconductors with Lewis acid species is not fully elaborated. The products of the doping reactions between Lewis acids and organic semiconductors have not been studied in detail. Here we focus on the macromolecular poly[bis(4-phenyl)(2,4-dimethylphenyl)]amine (PTAA) and molecular fluorinated anthradithiophene (diF-TES-ADT) organic semiconductors for addressing their chemical integrity after p-doping by the tris(pentafluorophenyl) borane [B(C₆F₅)₃] Lewis acid agent. The PTAA and diF-TES-ADT organic substrates are studied in mixtures with B(C₆F₅)₃ at three discrete concentration regimes. In the dilute solution regime, UV-Vis absorption spectroscopy verifies the effectiveness of p-doping by the changes observed in the absorption spectra of the solutions at increased B(C₆F₅)₃ content. In the concentrated solution regime, the reactivity of B(C₆F₅)₃ with PTAA and diF-TES-ADT is monitored by proton nuclear magnetic resonance (¹H-NMR) and electrospray ionization mass spectroscopy (ES-MS), as well as thin-layer chromatography (TLC). Finally, in the solid-state the photophysical properties of spin-coated PTAA:B(C₆F₅)₃ and diF-TES-ADT:B(C₆F₅)₃ films are examined as a function of their B(C₆F₅)₃ content. Density functional theory (DFT) calculations corroborate the experimental findings. Both theoretical and experimental results exclude the formation of Lewis adduct species in the PTAA:B(C₆F₅)₃ and diF-TES-ADT:B(C₆F₅)₃ systems. In agreement with recent literature, the B(C₆F₅)₃ reactivity is attributed to the Brønsted-type acidity of the hydrated B(C₆F₅)₃–OH₂ complex that induces p-doping via the protonation of the organic substrates. The formation of the B(C₆F₅)₃–OH₂ acidic agent is identified experimentally by its characteristic ¹H-NMR signal at 4.7 ppm. All results for the three concentration regimes provide evidence for the occurrence of PTAA and diF-TES-ADT decomposition in the presence of B(C₆F₅)₃. At high B(C₆F₅)₃ loadings, ES-MS spectroscopy and TLC analysis suggest that B(C₆F₅)₃ remains unreacted, revealing the catalytic role in the decomposition process of PTAA and diF-TES-ADT. The results suggest that after interacting with Lewis acids, organic semiconductors may undergo detrimental decomposition reactions. This potentially undesired chemical reactivity should be considered for evaluating the operation stability of the p-doped electronic devices.

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.

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 pK_a 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(a¹Δ_g), 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(a¹Δ_g). These results expand the available options in the toolbox of fluorescein-based fluorophores.

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.

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.

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.

Ein Komplex aus [10]Cycloparaphenylen ([10]CPP) mit dem Bisazafulleren (C₅₉N)₂ wurde experimentell und computerchemisch untersucht. In dieser Struktur sind zwei [10]CPP‐Ringe an das dimere Azafulleren gebunden, [10]CPP⊃(C₅₉N)₂⊂[10]CPP. Die beobachteten photophysikalischen und Redox‐Eigenschaften lassen auf eine elektronische Interaktion zwischen den Komponenten schließen, insbesondere mit dem zweiten [10]CPP. Im Gegensatz zu [10]CPP⊃C₆₀, in dem nur eine vernachlässigbare elektronische Kommunikation zwischen den Komponenten beobachtet wurde, konnte zwischen dem [10]CPP und dem (C₅₉N)₂ durch Lichtanregung ein Ladungstransferphänomen induziert werden, ähnlich einem mit einem CPP eingekapselten Metallofulleren. Solch elektronenreiche Fullerenspezies zeigen C₆₀‐artige Grundzustandseigenschaften und verhalten sich im angeregten Zustand wie Metallofullerene. Diese Eigenschaft eröffnet neue Möglichkeiten für die Konstruktion von funktionalen supramolekularen Architekturen mit organischen Materialien.