Chellaiah Arunkumar

Third-order nonlinear optical investigations of meso-tetrakis(2,3,5,6-tetrafluoro-N,N-dimethyl-4-anilinyl)porphyrin and its metal complexes.

We report here the experimental investigation on third-order nonlinear optical parameters of 5,10,15,20-tetrakis(2,3,5,6-tetrafluoro-N,N-dimethyl-4-anilinyl)porphyrin and its various metal complexes, using Z-scan technique at 532 nm. The third-order nonlinear optical susceptibilities (χ(3)) were of the order 10(-12) esu and are compared through degenerate four wave mixing (DFWM). The operating mechanism is reverse saturable absorption (RSA) as the effective excited-state absorption cross-section was found higher than ground state absorption cross-section as well as the magnitude of nonlinear absorption coefficient was found decreasing with on-axis input intensity. The compounds found to exhibit good optical limiting at 532 nm, 7 ns excitation steering applications in laser safety.

Axial ligand modified high valent tin(IV) porphyrins: synthesis, structure, photophysical studies and photodynamic antimicrobial activities on Candida albicans

Herein, we report the synthesis, structure, photophysical properties and photodynamic antimicrobial activities on Candida albicans of axial ligand modified high valent tin(IV) porphyrins, namely SnIV(OH)2T(4-CMP)P (1), SnIV(OH)2T(4-CP)P (2) and SnIV(O-NO2Ph)2T(4-CMP)P (3). The newly synthesized porphyrins were characterized by various spectroscopic methods and single crystal X-ray diffraction analysis. The crystal structures of the precursor porphyrin, SnIV(Cl)2T(4-CMP)P and 3 are well stabilized by various intermolecular interactions and porphyrin 3 shows complementary bonding interactions between the nitro groups (N⋯O) forming a one-dimensional array. The fluorescence lifetime of 3 is lower compared to other porphyrins which indicates that there is a considerable interaction between the tin(IV) porphyrin core and nitrophenyl system and this could be the reason for its significant phototoxicity. This is further evident from X-ray crystallography and DFT calculations. In the presence of light, tin(IV) porphyrins significantly inhibited the growth of C. albicans in liquid as well as in the solid agar medium and the growth inhibitory effects were much less under dark conditions. The porphyrin internalization as well as localization within the Candida cells were examined by fluorescence microscopic analysis. Our results suggest that the mechanism behind the photodynamic inactivation of C. albicans could be through the generation of singlet oxygen species within the cells.

Synthesis, structure, electrochemical, DNA interaction and antimicrobial studies of fluorinated trans-dicationic pyridinium porphyrins

A series of trans-pyridyl porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2′/3′/4′-pyridyl)porphyrin (1–3), trans-dicationic pyridinium porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2′/3′/4′-N-methylpyridyl)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 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 Kb of these dicationic porphyrins to DNA was found to be in the range of 105 to 106 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 1O2-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.

Influence of steric hindrance on the solvent-dependent absorption spectral behavior of highly brominated free base porphyrin and its Zn(II) complex

Electronic absorption spectra of highly brominated free base porphyrin, 2,3,7,8,12,13,17,18-octabromo-tetrakis(2′,6′-dibromo-3′,5′-dimethoxyphenyl)porphyrin, H2T(3′,5′-DMP)PBr16 and its Zn(II) complex were examined in various solvents. These derivatives exhibit red-shifted absorption spectral features in polar solvents relative to that observed in less polar or nonpolar solvents. The extent of red shifts observed in highly brominated porphyrins is less than those reported for the corresponding 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin, H2TPPBr8 and its Zn(II) complex. The crystal structure of the H2T(3′,5′-DMP)PBr16 showed saddle-shaped geometry with steric hindrance of the bromo groups on the opposite phenyl rings which provide limited open access to the core. The decreased red shift of the absorption spectral bands of MT(3′,5′-DMP)PBr16 (M = 2H, Zn(II)) derivatives when compared to unhindered MTPPBr8 is possibly due to the steric hindrance offered by the ortho-bromo groups rather than the electronic effects of the porphyrin π-system.

Fluorinated meso-tetraaryl Pt(II)-porphyrins: structure, photophysical, electrochemical, and phosphorescent oxygen sensing studies

Fluorinated Pt(II)-porphyrins (F1–F8) were synthesized, characterized; photophysical and electrochemical studies were conducted. The electronic absorption spectra of the complexes exhibited an intense Soret band (392–402 nm) and two hypsochromically shifted visible (Q) bands (508–510 and 538–541 nm). They also exhibited two emission bands (701–721 nm and 651–658 nm), corresponding to the T → S0 transition. The cyclic voltammetric studies of the porphyrins revealed the order of electron deficiency is as follows; F2 > F7 ≈ F8 > F5 > F4 > F3. The crystals of F3, F4, and F7 were structurally characterized and the crystal packing was mainly controlled by F⋯H, O⋯H, O⋯O, C⋯H close contacts. The oxygen sensing studies of the synthesized Pt(II)-porphyrins demonstrate that the highest sensitivity was observed for F8 compared to other complexes. The modified Stern–Volmer or two-site model provides the highest weighted quenching constant (KSV) of 0.068 Torr−1 for F8, which is twofold of the reference compound F1.

A “turn-on-and-off” pH sensitive BODIPY fluorescent probe for imaging E. coli cells

We report fluorescent turn-on-and-off pH BODIPY probes which show a drastic shift in pKa values upon introducing electron withdrawing substituents on the meso-phenyl ring. The sensors utilize 4-amino- and 4-hydroxyl groups as proton receptors and work by intramolecular photoinduced electron transfer (PET) under acidic pH conditions. The acid sensing mechanism is proven by 1H NMR, IR spectroscopic methods and electrochemical studies. Unlike previous reports, the pH response of the –OH group in compound 3 is due to the formation of –OH2+. Compounds 1 and 4 are highly selective to H+ over other metal ions and displayed good photostability and reversibility. The utility of acid sensitive behavior of 1 and 4 to visualize extreme acidity is also demonstrated using the model organism E. coli.

Protonation and axial ligation intervened fluorescence turn-off sensing of picric acid in freebase and tin(IV) porphyrins

Freebase and tin(IV)-porphyrins are examined for the selective detection of picric acid and their affinity is revealed by spectroscopic titrations and X-ray structures. The sensing is mediated through protonation and axial ligation in 1–5 and 6–9 respectively. Fluorescent lifetime studies show that the quenching is dynamic in the freebase and static in tin(IV)-porphyrins.

Pentafluorophenyl dipyrrin as probe for transition metal ion detection and bioremediation in Bacillus subtilis and Bacillus cereus

We report a highly sensitive and selective “turn-on” fluorescent/colorimetric probe, 5-(pentafluorophenyl)dipyrrin (1), for selected transition metal ions in aqueous medium at biological pH. The limit of detection for Zn(II), Hg(II), Cu(II) and Ni(II) is found to be 0.18 μM, 0.28 μM, 13.01 μM and 18.31 μM respectively. The mechanism of complexation is confirmed as a 1 : 2 ratio of metal to ligand by Jobs plot analysis and mass spectrometry. The practical application of the probe in bioremediation of metal ions by B. subtilis (BS) and B. cereus (BC) is demonstrated and the tolerance level of these microorganisms against metal ions is identified. The emission peak centered at a long wavelength of 548 to 558 nm indicates the potential application of this probe in bio-imaging Zn(II) and Hg(II) by fluorescence microscopy. Thus, it is possible to track the ions absorbed by BS and BC.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs

A series of mono- and di-brominated BODIPYs (1–5) was synthesized and characterized with a view to study the performance of dyes towards antibacterial activity. Regioselective bromination at the 2- and 2,6-positions of the BODIPY core was achieved with quantitative yield. The bromination of meso-(4-hydroxyphenyl) BODIPY (5) yielded an unexpected dibromo derivative, where the bromine groups were installed at the 3,5-positions of the phenyl ring rather than the 2,6-positions of the BODIPY core, which is confirmed and supported by UV-visible, fluorescence, and 1H NMR spectroscopic analyses, electrochemical studies, and also by single crystal X-ray crystallography. We observed a red shift of ∼16 nm in the absorption and 20–29 nm in the emission spectra in CH2Cl2 for the installation of each bromine group at the BODIPY core. The small difference between the first reduction potentials of the parent and dibromo derivative (5 and 5b) reveal that dibromination does not occur on the pyrrolic moiety. The intermolecular interactions involving C⋯H, F⋯H, H⋯H, and Br⋯H are the key factors in stabilizing the molecular crystal packing. The antibacterial properties of these dyes were investigated and the brominated derivatives showed better antibacterial effects than their corresponding parent BODIPYs, particularly the unusual dibromo derivative, 5b.

χ(3) measurements of axial ligand modified high valent tin(IV) porphyrins using degenarete four wave mixing at 532nm

Porphyrins and metalloporphyrins are unique class of molecules for Nonlinear Optical applications because of their unique structure of altering the central metal atom, large extended π-system, high thermal stability, tunable shape, symmetry and synthetic versatility Here, we report χ(3) Measurements of a simple phenyl porphyrins and its highvalent tin(IV) porphyrins with Bromination characterized by UV-Visible spectroscopic method. In this study, we employed the Degenerate Four Wave Mixing technique using forward Boxcar geometry with an Nd:YAG nano second pulsed laser as source and it was found that the tin(IV) porphyrin with Bromination exhibits good χ(3) value and figure of merit.