Ground and Excited State Dynamics of Core-modified Normal and Expanded Porphyrins

Photoredox Catalysis by 21-Thiaporphyrins: A Green and Efficient Approach for C-N Borylation and C-H Arylation

Photoredox catalysis provides a green and sustainable alternative for C-H activation of organic molecules that eludes harsh conditions and use of transition metals. The photocatalytic C-N borylation and C-H arylation mostly depend on the ruthenium and iridium complexes or eosin Y and the use of porphyrin catalysts is still in infancy. A series of novel 21-thiaporphyrins (A2B2 and A3B type) were synthesized having carbazole/phenothiazine moieties at their meso-positions and screened as catalysts for C-N borylation and C-H arylation. This paper demonstrates the 21-thiaporphyrin catalyzed C-N borylation and het-arylation of anilines under visible light. The method utilizes only 0.1 mol % of 21-thiaporphyrin catalyst under blue light for the direct C-N borylation and het-arylation reactions. A variety of substituted anilines were used as source for expensive and unstable aryl diazonium salts in the reactions. The heterobiaryls and aryl boronic esters were obtained in decent yields (up to 88 %). Versatility of the 21-thiaporphyrin catalyst was tested by thiolation and selenylation of anilines under similar conditions. Mechanistic insight was obtained from DFT studies, suggesting that 21-thiaporphyrin undergo an oxidative quenching pathway. The photoredox process catalyzed by 21-thiaporphyrins offers a mild, efficient and metal-free alternative for the formation of C-C, C-S, and C-Se bonds in aryl compounds; it can also be extended to borylation reaction.

Two-photon absorption of 28-hetero-2,7-naphthiporphyrins: expanded carbaporphyrinoid macrocycles

The one- and two-photon absorption (1PA and 2PA) properties of three expanded aceneporphyrinoids, 28-thia-, 28-selena- and 28-tellura-2,7-naphthiporphyrin, have been studied. The open-aperture Z-scan technique was used to determine two-photon absorption cross-sections in the near infrared range using an amplified femtosecond laser system. The maximum values of the cross sections were found to be 99, 200 and 650 GM at 900 nm and 1, 13 and 31 GM at 1400 nm for the three investigated compounds, respectively. These results demonstrate enhanced 2PA properties compared with well-known porphyrin photosensitizers, such as Foscan®, showing the potential of porphyrin core modification for optimizing infrared nonlinear absorbers.

Synthesis, spectroscopy studies, and theoretical calculations of new fluorescent probes based on pyrazole containing porphyrins for Zn(II), Cd(II), and Hg(II) optical detection

New pyrazole-porphyrin conjugates were successfully prepared from a reaction of β-porphyrin-chalcone derivatives with phenylhydrazine in acetic acid followed by an oxidative step. This fast and efficient synthetic approach provided the expected compounds in yields up to 82%. The sensing ability of the new porphyrin-pyrazole derivatives to detect the metal ions Ag(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Cr(3+) was studied by spectrophotometric and spectrofluorimetric titrations. In the presence of Zn(2+), the conjugates exhibit changes in the emission spectra that are desired for a ratiometric-type fluoroionophoric detection probe. The studies were extended to gas phase, where the pyrazole-porphyrin conjugates show ability to sense metal ions with high selectivity toward Cu(2+) and Ag(+), and in poly(methyl methacrylate) doped films with promising results for Zn(2+) detection.

Nonlinear Optical Properties and Excited-State Dynamics of Highly Symmetric Expanded Porphyrins

A strong correlation among calculated Nucleus-Independent Chemical Shift (NICS) values, molecular planarity, and the observed two-photon absorption (TPA) values was found for a series of closely matched expanded porphyrins. The expanded porphyrins in question consisted of [26]hexaphyrin, [28]hexaphyrin, rubyrin, amethyrin, cyclo[6]pyrrole, cyclo[7]pyrrole, and cyclo[8]pyrrole containing 22, 24, 26, 28, and 30 pi-electrons. Two of the systems, [28]hexaphyrin and amethyrin, were considered to be antiaromatic as judged from a simple application of Hückel's [4n + 2] rule. These systems displayed positive NICS(0) values (+43.5 and +17.1 ppm, respectively) and gave rise to TPA values of 2600 and 3100 GM, respectively. By contrast, a set of congeners containing 22, 26, and 30 pi-electrons (cyclo[n]pyrrole, n = 6, 7, and 8, respectively) were characterized by a linear correlation between the NICS and TPA values. In the case of the oligopyrrolic macrocycles containing 26 pi-electron systems, a further correlation between the molecular structure and various markers associated with aromaticity was seen. In particular, a decrease in the excited state lifetimes and an increase in the TPA values were seen as the flexibility of the systems increased. Based on the findings presented here, it is proposed that various readily measurable optical properties, including the two-photon absorption cross-section, can provide a quantitative experimental measure of aromaticity in macrocyclic pi-conjugated systems.

In Vitro and In Vivo Investigations on the Photodynamic Activity of Core-modified Expanded Porphyrin—Ammonium Salt of 5,10,15,20-tetrakis-(meso-p-sulfonato phenyl)-25,27,29-trithia Sapphyrin¶†

The core modification of expanded porphyrins has been proved to have better photochemical properties, which are favorable for photodynamic therapy (PDT) applications. In this context, this study was aimed to investigate the in vitro and in vivo photodynamic activity of one such core-modified expanded porphyrin, namely, ammonium salt of 5,10,15,20-tetrakis-(meso-p-sulfonato phenyl)-25,27,29-trithia sapphyrin. For the in vitro studies, human erythrocytes were used as a membrane semimodel system to investigate the partitioning ability and drug-uptake characteristics. The partition studies on the membrane semimodel system revealed that maximum partitioning occurs at 12 microgm/mL concentration, and from the drug-uptake studies it is observed that maximum amount of the sensitizer is bound to the erythrocyte membranes during a 45 min incubation period. Photohemolysis studies at different concentrations of the sensitizer and exposure time showed maximum damage at 5 microgm/mL and 30 min exposure time. In vivo studies were performed on 7,12-dimethylbenz(a)nthracene-induced superficial squamous cell carcinoma on mouse skin. The sensitizer at a concentration of 2.5% in 2.0% dimethyl sulfoxide was applied topically on the tumor spot. After 1 h incubation the tumor spot was exposed to laser irradiation from Nd-YAG laser at its second harmonic wavelength of 532 nm. The photodynamic efficacy was estimated by tumor volume measurements at regular intervals after the treatment. One month after PDT exposure a 3.9-fold decrease in the tumor volume was observed with respect to the tumor volume before treatment. The treatment efficacy was further confirmed by histological and fluorescence spectroscopic evaluations of the tissue biopsy sample from the treated area. The results of our study suggest that the ammonium salt of 5,10,15,20-tetrakis-(meso-p-sulfonato phenyl)-25,27,29-trithia sapphyrin may find possible applications in the new modality of cancer treatment.