Investigation of J-Aggregates of 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl) Porphyrin in Aqueous Solutions
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Published:2023-10-26
Issue:21
Volume:13
Page:2832
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ISSN:2079-4991
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Container-title:Nanomaterials
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language:en
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Short-container-title:Nanomaterials
Author:
Abdelaziz Balkis12, Sarà Mariachiara3, Ayachi Sahbi2, Zagami Roberto3ORCID, Patanè Salvatore1ORCID, Romeo Andrea3ORCID, Castriciano Maria Angela3ORCID, Monsù Scolaro Luigi3ORCID
Affiliation:
1. Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina V.le F. Stagno D’Alcontres, 31, 98166 Messina, Italy 2. Laboratory of Physico-Chemistry of Materials (LR01ES19), Faculty of Sciences, Avenue of the Environment University of Monastir, Monastir 5019, Tunisia 3. Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina V.le F. Stagno D’Alcontres, 31, 98166 Messina, Italy
Abstract
The highly distorted water-soluble 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (Br8TPPS44−) is readily protonated under acidic pH, forming the diacid H2Br8TPPS42− and subsequently the zwitterionic H4Br8TPPS4, which eventually evolves into J-aggregates. These latter species exhibit a relevant bathochromic shift with respect to the monomer with a quite sharp band due to motional narrowing. The depolarization ratio measured in resonant light scattering spectra allows estimating a tilt angle of ~20° of the porphyrins in the J-aggregate. The kinetic parameters are obtained by applying a model based on the initial slow nucleation step, leading to a nucleus containing m monomers, followed by fast autocatalytic growth. The kc values for this latter step increase on decreasing the acid concentration and on increasing the porphyrin concentration, with a strong power-law dependence. No spontaneous symmetry breaking or transfer of chirality from chiral inducers is observed. Both Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS) point to the presence, in both the solid and solution phases, of globular-shaped aggregates with sizes close to 130 nm. Density functional theory (DFT) calculations performed on simplified models show that (i) upon protonation, the saddled conformation of the porphyrin ring is slightly altered, and a further rotation of the aryl rings occurs, and (ii) the diacid species is more stable than the parent unprotonated porphyrin. Time-dependent DFT analysis allows comparing the UV/Vis spectra for the two species, showing a consistent red shift upon protonation, even if larger than the experimental one. The simulated Raman spectrum agrees with the experimental spectrum acquired on solid samples.
Funder
Next Generation EU, PNRR Samothrace Project
Subject
General Materials Science,General Chemical Engineering
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