On the photophysics of nanographene – investigation of functionalized hexa-peri-hexabenzocoronenes as model systems

In the current study, we report on hexa-peri-hexabenzocoronenes (HBCs) as a representative model for nanographene. To this end, we synthesized a family of functionalized HBCs and investigated the impact of the substituents on the π-extended system of the HBCs. DFT and TD-DFT calculations suggested a charge transfer character, which intensifies as the electron density withdrawing effects of the substituents (–M-effect) increase. Unambiguous corroboration of the charge transfer character in the case of the NO2-substituents was realized with steady-state absorption and fluorescence experiments, which focused on the dependencies on solvent polarity and temperature featuring. Going beyond HBCs with NO2-substituents time-correlated single photon counting, femtosecond and nanosecond transient absorption spectroscopy unveil long-lived singlet and triplet excited states. As a complement, we performed electrochemical and spectroelectrochemical measurements. These were carried out to shed light onto the nature of functionalized HBCs as electron acceptors and/or donors, on one hand, and their corresponding spectroscopic signatures, on the other hand. All of the aforementioned enabled intermolecular charge separation assays with, for example, suitable electron acceptors by steady-state and time-resolved spectroscopies

Panchromatic light funneling through the synergy in hexabenzocoronene–(metallo)porphyrin–fullerene assemblies to realize the separation of charges

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data

Controlling the self-metalation rate of tetraphenylporphyrins on Cu(111) via cyano functionalization

The reaction rate of the self-metalation of free-base tetraphenylporphyrins (TPPs) on Cu(111) increases with the number of cyano groups (n=0, 1, 2, 4) attached at the para positions of the phenyl rings. The findings are based on isothermal scanning tunneling microscopy (STM) measurements. At room temperature, all investigated free-base TPP derivatives adsorb as individual molecules and are aligned with respect to densely packed Cu substrate rows. Annealing at 400K leads to the formation of linear dimers and/or multimers via CN-Cu-CN bonds, accompanied by self-metalation of the free-base porphyrins following a first-order rate equation. When comparing the non-cyano-functionalized and the tetracyano-functionalized molecules, we find a decrease of the reaction rate by a factor of more than 20, corresponding to an increase of the activation energy from 1.48 to 1.59eV. Density functional theory (DFT) calculations give insights into the influence of the peripheral electron-withdrawing cyano groups and explain the experimentally observed effects.57321007410079Agências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

3-Hydroxy-propanamidines, a new class of orally active antimalarials targeting Plasmodium falciparum

3-Hydroxypropanamidines are a new promising class of highly active antiplasmodial agents. The most active compound 22 exhibited excellent antiplasmodial in vitro activity with nanomolar inhibition of chloroquine-sensitive and multidrug-resistant parasite strains ofPlasmodium falciparum (with IC50 values of 5 and 12 nM against 3D7 and Dd2 strains, respectively) as well as low cytotoxicity in human cells. In addition, 22 showed strong in vivo activity in thePlasmodium berghei mouse model with a cure rate of 66% at 50 mg/kg and a cure rate of 33% at 30 mg/kg in the Peters test after once daily oral administration for 4 consecutive days. A quick onset of action was indicated by the fast drug absorption shown in mice. The new lead compound was also characterized by a high barrier to resistance and inhibited the heme detoxification machinery in P. falciparum