Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H(2)F(20)TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution. At room temperature in DCM, free base (H(2)F(20)TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime tauf=9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic amines to a solution containing H(2)F(20)TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence emission. Upon addition of amines there was no change in optical absorption spectra of H(2)F(20)TPP. The fluorescence quenching rate constants ranged from 1 x 10(9) to 4 x 10(9) s(-1), which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern-Volmer kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H(2)F(20)TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer rate as function of free energy change (DeltaG(0)) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence quenching of free base neutral porphyrins in homogeneous organic solvent ever known.

Preparation and characterization of absolutely pure and stable nanoparticles of 5,10,15,20-meso-tetrakis phenyl porphyrin (TPP) and catalytically repute 5,10,15,20-meso-tetrakis pentaflurophenyl porphyrin (H 2 F 20 TPP) by improved 'reprecipitation method' is described. The innovation of this modified 'reprecipitation method' lies on the judicial selection of organic solvent and amount of porphyrin solution to be injected in the aqueous media. Exactly similar process produces relatively small nanoparticles for TPP than that of H 2 F 20 TPP while the stability of the H 2 F 20 TPP nanoparticles is bit higher than nanoparticles of TPP. Absorption and emission spectra reveal that the formation of nanoparticles for both the cases is induced by J-and H-type aggregation. DFT calculations predict the optimized geometries and frontier molecular orbital, which favours the strength of face-to-face interaction with neighbour molecules to be more facile for TPP than that of H 2 F 20 TPP helping the latter to form bigger and relatively more stable and free-standing nanoparticles. The use of no other compounds except dichloromethane, a highly volatile organic solvent and respective porphyrins give absolutely pure nanoparticles. This improved method will lead to produce organic nanoparticles of π-conjugated systems easily and efficiently.

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A simple and efficient approach to (þ)-nephrosteranic acid from dodecanol as a starting material is described, employing Sharpless asymmetric epoxidation, ring-closing metathesis, and Gilman addition of a vinyl group as key steps. These key reactions allow fast access to trisubstituted c-butyrolactone. The molecule synthesized exhibits potent antifungal, antibacterial, and cytotoxic activities against all the tested strains.

Stereoselective Synthesis of (+)-Nephrosteranic Acid by Ring-Closing Metathesis and Its Biological Evaluation. -A stereoselective synthesis of (+)-nephrosteranic acid (VIII) is presented. The biological evaluation shows that (VIII) shows potent antifungal, significant antibacterial and significant cytotoxic activities. -(PEREPOGU, A. K.; RAMAN, D.; MURTY, U. S. N.; RAO*, V. J.; Synth. Commun. 40 (2010) 5, 686-696, DOI:10.1080/00397910903011337; Org. Chem. Div., Indian Inst. Chem. Technol., Hyderabad 500 607, India; Eng.) -M. Bohle 32-205