Nivedita Chaudhri

Colorimetric “naked eye” detection of CN−, F−, CH3COO− and H2PO4− ions by highly nonplanar electron deficient perhaloporphyrins

Highly nonplanar perhaloporphyrin-based receptors have been synthesized and characterized by various spectroscopic techniques. Nonplanar and electron deficient nature was authenticated by electronic spectral, electrochemical redox and protonation–deprotonation studies. The colorimetric “naked eye” anion sensing ability of these sensors was probed by spectroscopic and electrochemical studies. These receptors were found to be highly selective and sensitive for the basic anions, such as CN−, F−, OAc− and H2PO4−, over the tested anions and were able to detect these anions even at nanomolar concentrations via anion induced deprotonation. These perhaloporphyrin receptors have been recovered from receptor–anion host–guest complexes formed during sensing events by acid treatment and were reused for the detection of basic anions without loss of their sensing ability.

Facile Conversion of Ni(II) Cyclopropylchlorins into Novel β-Substituted Porphyrins through Acid-Catalyzed Ring-Opening Reaction.

The conversion of cyclopropylchlorins into porphyrins represents a key step in the synthetic manipulation of macrocycles with tunable physical and chemical properties. Herein, we report a facile method for the synthesis of novel β-substituted porphyrins from cyclopropylchlorins. A series of Ni(II) cyclopropylchlorins was converted into the corresponding Ni(II) and free base porphyrins using TFA and H2SO4 under mild reaction conditions in good yields (75-86%). The new chlorins and porphyrins were characterized by various spectroscopic techniques and the single-crystal X-ray diffraction method. The reaction proceeds very fast (<5 min.) with complete conversion of chlorin into porphyrin with distinct color change. Facile conversion, shorter reaction time scale, and good yield (75-86%) without any side products are the significant features of this new protocol. These porphyrinoids exhibited red-shifted electronic spectral features with varying degrees nonplanar conformation, tunable redox properties, and porphyrin core basicity.

Versatile Synthetic Route for β-Functionalized Chlorins and Porphyrins by Varying the Size of Michael Donors: Syntheses, Photophysical, and Electrochemical Redox Properties

One-pot facile synthesis and characterization of novel β-substituted meso-tetraphenylporphyrins and/or chlorins were described. The high regioselective reactivity of active methylene compounds in Michael addition reaction was reported to access β-substituted trans-chlorins. Size-dependent approach was applied for the fine-tuning of product formation from porphyrins to chlorins. Notably, we were able to isolate mono/trisubstituted porphyrin and/or di/tetra-substituted chlorin from one-pot synthesis for the first time in porphyrin chemistry. Single-crystal X-ray diffraction analysis revealed the quasiplanar to moderate nonplanar conformation of chlorins due to trans orientation of β-substituents, whereas porphyrins exhibited higher mean plane deviation from 24-atom core (Δ24) as compared to chlorins. β-Functionalized chlorins exhibited lower protonation constants and much higher deprotonation constants as compared to porphyrins revealing the combined effect of the conformation of macrocyclic core and the electronic nature of β-substituents. Facile synthesis of porphyrins and/or chlorins based on the size of Michael donor employed and in turn resulted in tunable photophysical and electrochemical redox properties are the significant features of the present work.

Antimicrobial photodynamic therapy: Single-walled carbon nanotube (SWCNT)-Porphyrin conjugate for visible light mediated inactivation of Staphylococcus aureus

Due to the excessive use of antibiotics over the years, the microorganisms have developed resistance to numerous drugs. The growth of multi-resistant organisms (MROs) heads due to the insufficient treatment with the currently available medications which present a great threat to the biotic component of the environment as well as to the food technology sectors. The goal of this research was to develop a nano-composite made up of single-walled carbon nanotubes (SWCNTs) and amine-functionalized porphyrin, which could further be used for the anti-microbial studies in presence of visible light showing photodynamic effect to inactivate cells. Photodynamic antimicrobial chemotherapy is gaining significant interest due to its capabilities as an innovative form of antimicrobial treatment. The development of anti-microbial photodynamic therapy (a-PDT) is a non-antibiotic access to inactivate microorganisms. We examined the synthesis of amine-functionalized porphyrin and conjugated it to the oxidised single-walled carbon nanotubes (SWCNTs). By the use of appropriate amount of single-walled carbon nanotubes (SWCNTs), we have shown the interaction between the porphyrin conjugated nanotubes and the bacterial cells in presence of visible light led to the cell membrane damage, concluding that SWCNT-porphyrin conjugates can be used as an antibacterial agent. The characterization of the oxidised SWCNT and SWCNT-porphyrin conjugates was determined by field emission scanning electron microscopy (FE-SEM), which provides detailed information about the composition and the morphological analysis. The particle size measurements were carried out by transmission electron microscopy (TEM). On investigating under the florescence microscopy, red fluorescence was observed. Thus, these properties demand us to design this facile material comprised of SWCNT-aminoporphyrin conjugates that shows potent antibacterial activity.

Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A3B and A4 free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies (η) of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4′-pyridyl)-20-(4′-carboxyphenyl)porphyrin (H2TriPyMCPP), 5,10,15,20-tetrakis(4′-aminophenyl)porphyrin (H2TAPP) and 5-(4′-pyridyl)-10,15,20-tris(4′-carboxyphenyl)porphyrin (H2MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are shown to be superior sensitizers as compared to carboxyphenylporphyrins. The investigation of effect of functional group and position of functional group of porphyrin dye on DSSC can serve as an important tool to guide further selection and synthesis of potential candidates as sensitizers.

Synthesis and structural, photophysical, electrochemical redox and axial ligation properties of highly electron deficient perchlorometalloporphyrins and selective CN− sensing by Co(II) complexes

A straightforward synthetic route has been adopted to synthesize highly nonplanar electron deficient perchlorometallo-porphyrins. Herein, we report the synthesis and characterization of MTPP(NO2)Cl7 where M = CoII, NiII, CuII and ZnII. Further, we examined their optical and electrochemical redox properties and the results are compared with MTPPCl8. MTPP(NO2)Cl7 exhibited red-shifted (∼10–15 nm) absorption spectra relative to MTPPCl8 due to the strong electron withdrawing nature of the nitro group. Mixed β-substitution alters the electrochemical redox properties to such an extent that an appreciable increase in the anodic shift in reduction potential (200–300 mV) is observed for MTPP(NO2)Cl7 relative to MTPPCl8 whereas only a minimal shift (15–50 mV) in the oxidation potential is observed. Nonplanarity of the macrocyclic core was investigated by single crystal X-ray analysis and DFT calculations. A higher ΔCβ (0.706 A) for 1d as compared to 2d (0.642 A) undoubtedly signifies nonplanarity induced by the nitro group. To substantiate the effect of mixed substitution, we performed axial ligation studies of Zn(II) complexes with nitrogenous bases and basic anions and found higher log β2 values as well as a linear relation between log β2 and pKa as compared to perbromoporphyrins. Highly electron deficient β-substituted Co(II) porphyrins (1a and 2a) were utilized as novel sensors for selective rapid visual detection of CN− ions.

Selective Conversion of Planar trans-Chlorins into Highly Twisted Doubly Fused Porphyrins or Chlorins via Oxidative Fusion

β-to- o-phenyl doubly fused porphyrins (DFPs) or chlorins (DFCs) were selectively synthesized by facile oxidative fusion of trans-chlorins using 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (DDQ) in good-to-excellent yields (70-92%) under mild reaction conditions with high atom economy. The selectivity in product formation (difused porphyrin or chlorin) was controlled by the presence or absence of a Ni(II) ion in the macrocyclic core. Notably, nickel(II) trans-chlorins selectively yielded DFPs, whereas free-base trans-chlorins afforded only DFCs. The synthesized fused porphyrinoids exhibited significantly red-shifted electronic spectral features (Δλmax = 16-53 nm) of the Soret band due to the extended π conjugation and highly twisted macrocyclic conformation (twist angle ∼20-34°). Inner-core NHs of fused chlorins exhibited a tremendous downfield shift (Δδ = 1.71-2.02 ppm) compared to their precursors. The overall protonation constants for indanedione-substituted free-base-difused chlorins (4-6) were profoundly higher (∼20-50-fold) compared to dicyanomethyl-appended free-base-difused chlorins (10-12) because of the combined effect of the electronic nature of the β-substituents and nonplanarity of the macrocyclic core. The first oxidation potential of H2DFC(MN)2Ph2 (12) was 0.54 V cathodically shifted with respect to H2DFC(MN)2 (10) because of the electron-donating nature of the β-phenyl groups, which resulted in extensive destabilization of the highest occupied molecular orbital.

Nickel-Induced Skeletal Rearrangement of Free Base trans-Chlorins into Monofused NiII-Porphyrins: Synthesis, Structural, Spectral, and Electrochemical Redox Properties

Several ruffled β-to- ortho-phenyl monofused metalloporphyrins (MIIMFPs) with 1,3-indanedione functionality have been synthesized by oxidative fusion of free base trans-chlorins via nickel insertion followed by the skeletal rearrangement of macrocycle. The synthesized monofused porphyrins exhibited red-shifted electronic spectral features as compared to precursor, trans-chlorins or structurally related unfused porphyrins (mono/tri-β-substituted porphyrins) due to extended π-conjugation and nonplanar conformation of the macrocyclic core. Four of the synthesized porphyrins were structurally characterized by X-ray diffraction analysis. Ring fusion resulted in twisted macrocyclic conformation, and the twist angles (the angle between 24-atom core and fused part) were found to be in the range of 20.97° to 27.97°. NiMFP(IND)Ph2 (3b) exhibited modestly ruffled conformation of the macrocyclic core which was further confirmed by higher Δ24 (0.362 Å) and ΔCβ (0.279 Å) values. Free base monofused porphyrins have shown upfield shifted (Δδ = 0.27-0.29 ppm) inner core NHs as compared to precursors ( trans-chlorins), whereas much downfield shifted (Δδ = 0.9 ppm) as compared to H2TPP. Electron-rich Ni(II) complexes, that is, NiMFP(IND)R2 (where R = H and Ph) (1b and 3b), exhibited metal centered oxidation (NiII/NiIII) due to extended π-conjugation of macrocyclic core and electron-donating β-substituents. Facile synthesis with good yields (60-90%), unexpected nickel-induced oxidative fusion, and selective conversion of trans-chlorins into monofused NiII-porphyrins are the significant features of the present work.