Excited dimers (excimers) formed by aromatic molecules are important in biological systems as well as in chemical sensing. The structure of many biological systems is governed by excimer formation. Since theoretical studies of such systems provide important information about mutual arrangement of aromatic molecules in structural biology, we carried out extensive calculations on the benzene excimer using EOM-CCSD, RI-CC2, CASPT2, and TD-DFT approaches. For the benzene excimer, we evaluate the reliability of the TD-DFT method based on the B3LYP, PBE, PBE0, and ωPBEh functionals. We extended the calculations to naphthalene, anthracene, and pyrene excimers. We find that nearly parallel stacked forms are the minimum energy structure. On the basis of the benzene to pyrene excimers, we might roughly estimate the equilibrium layer-to-layer distance for bilayer-long arenes in the first singlet excited state, which is predicted to be bound.

High-valent manganese(IV or V)-oxo porphyrins are considered as reactive intermediates in the oxidation of organic substrates by manganese porphyrin catalysts. We have generated Mn(V)- and Mn(IV)-oxo porphyrins in basic aqueous solution and investigated their reactivities in C-H bond activation of hydrocarbons. We now report that Mn(V)- and Mn(IV)-oxo porphyrins are capable of activating C-H bonds of alkylaromatics, with the reactivity order of Mn(V)-oxo>Mn(IV)-oxo; the reactivity of a Mn(V)-oxo complex is 150 times greater than that of a Mn(IV)-oxo complex in the oxidation of xanthene. The C-H bond activation of alkylaromatics by the Mn(V)- and Mn(IV)-oxo porphyrins is proposed to occur through a hydrogen-atom abstraction, based on the observations of a good linear correlation between the reaction rates and the C-H bond dissociation energy (BDE) of substrates and high kinetic isotope effect (KIE) values in the oxidation of xanthene and dihydroanthracene (DHA). We have demonstrated that the disproportionation of Mn(IV)-oxo porphyrins to Mn(V)-oxo and Mn(III) porphyrins is not a feasible pathway in basic aqueous solution and that Mn(IV)-oxo porphyrins are able to abstract hydrogen atoms from alkylaromatics. The C-H bond activation of alkylaromatics by Mn(V)- and Mn(IV)-oxo species proceeds through a one-electron process, in which a Mn(IV)-oxo porphyrin is formed as a product in the C-H bond activation by a Mn(V)-oxo porphyrin, followed by a further reaction of the Mn(IV)-oxo porphyrin with substrates that results in the formation of a Mn(III) porphyrin complex. This result is in contrast to the oxidation of sulfides by the Mn(V)-oxo porphyrin, in which the oxidation of thioanisole by the Mn(V)-oxo complex produces the starting Mn(III) porphyrin and thioanisole oxide. This result indicates that the oxidation of sulfides by the Mn(V)-oxo species occurs by means of a two-electron oxidation process. In contrast, a Mn(IV)-oxo porphyrin complex is not capable of oxidizing sulfides due to a low oxidizing power in basic aqueous solution.

A series of trans-pyridyl porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2ꞌ/3ꞌ/4ꞌ-pyridyl)porphyrin (1−3), trans-dicationic pyridinium porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2ꞌ/3ꞌ/4ꞌ-Nmethylpyridyl)porphyrins (4−6) and their copper(II) and zinc(II) derivatives were synthesized. These compounds were characterized using various spectroscopic methods, electrochemical and single crystal X-ray crystallographic studies. The trans-dicationic porphyrin derivatives exhibit red shifted absorption spectra over the simple pyridyl porphyrins. The reduction potentials of trans-pyridyl porphyrins are more positive than those of MTPPs. Crystal structure of 3c is forming networks of molecules through Zn-N coordination displaying large number of channels. The intermolecular interactions involving fluorine contributes considerably to the crystal packing in all the structures which was further confirmed by computational Hirshfeld surface analysis. The dicationic porphyrins were further explored for its DNA interaction abilities and antimicrobial activities. The UV-visible and fluorescence spectroscopic titrations indicate that the porphyrins bind with the calf thymus DNA by outside groove binding mode with or without self-stacking. The intrinsic binding constants K b of these dicationic porphyrins to DNA was found to be in the range of 10 5 −10 6 M −1 . The results reveal that among the three sets of porphyrins (4−6), the 3-/4-pyridyl derivatives display higher DNA binding activities compared to the 2-pyridyl analogues.The photocleavage experiments disclose that the porphyrins employ 1 O 2 -mediated mechanism in cleaving DNA and the freebase and zinc(II) derivatives show better photoinduced cleavage ability compared to its copper(II) analogues. The dicationic porphyrins also show significant antimicrobial activities than those of non-fluorinated analogues.Trans-dicationic pyridinium porphyrins: Synthesis, structure, electrochemical, DNA interaction and antimicrobial studies of fluorinated trans-pyridyl and trans-dicationic pyridinium porphyrins are reported and the studies indicate that they are superior artificial nucleases than its non-fluorinated analogues; bind with the calf thymus DNA by outside groove binding mode with or without self-stacking, also show significant antimicrobial activities than those of nonfluorinated analogues.

Photophysical studies, fluorescence imaging, single crystal X-ray structure analysis and DFT calculations revealed that compounds2and3show enhanced phototoxicity towardsCandida albicanscompared to compound1.

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