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Title: J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin

Abstract

The title porphyrin was dissolved in the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF4], and triggered to assemble into J-aggregates by the addition of incremental volumes of water containing various amounts of acid (0.1, 0.2, or 1.0 M HCl). In contrast to recent studies, the current investigation is unique in that it centers on media that contain a predominant ionic liquid component (2.9 5.4 M [bmim][BF4]), as opposed to an aqueous electrolyte containing a small fraction of ionic liquid as dissociated solute. Complex aggregation and underlying photophysical behavior are revealed from absorption spectroscopy, steady-state fluorescence, and resonance light scattering studies. Upon addition of aqueous HCl, the efficient formation of H4TPPS2 J-aggregates from the diprotonated form of meso-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4) occurs in [bmim][BF4]-rich media in a manner highly dependent upon the acidity, TPPS concentration, and solvent composition. The unique features of TPPS aggregation in this ionic liquid were elucidated, including the surprising disassembly of J-aggregates at higher aqueous contents, and our results are described qualitatively in terms of the molecular exciton theory. Finally, the potential of this system for the optical sensing of water at a sensitivity below 0.5 wt% is demonstrated. Overall, our findings accentuate how little is known about functional self-assemblymore » within ionic liquids and suggest a number of avenues for exploring this completely untouched research landscape.« less

Authors:
 [1];  [2];  [2];  [2];  [1]
  1. Indian Institute of Technology, Delhi
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1078210
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Chemistry Chemical Physics; Journal Volume: 12; Journal Issue: 8
Country of Publication:
United States
Language:
English

Citation Formats

Ali, Maroof, Kumar, Vinod, Baker, Sheila N, Baker, Gary A, and Pandey, Siddharth. J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin. United States: N. p., 2010. Web. doi:10.1039/b920500d.
Ali, Maroof, Kumar, Vinod, Baker, Sheila N, Baker, Gary A, & Pandey, Siddharth. J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin. United States. doi:10.1039/b920500d.
Ali, Maroof, Kumar, Vinod, Baker, Sheila N, Baker, Gary A, and Pandey, Siddharth. 2010. "J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin". United States. doi:10.1039/b920500d.
@article{osti_1078210,
title = {J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin},
author = {Ali, Maroof and Kumar, Vinod and Baker, Sheila N and Baker, Gary A and Pandey, Siddharth},
abstractNote = {The title porphyrin was dissolved in the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF4], and triggered to assemble into J-aggregates by the addition of incremental volumes of water containing various amounts of acid (0.1, 0.2, or 1.0 M HCl). In contrast to recent studies, the current investigation is unique in that it centers on media that contain a predominant ionic liquid component (2.9 5.4 M [bmim][BF4]), as opposed to an aqueous electrolyte containing a small fraction of ionic liquid as dissociated solute. Complex aggregation and underlying photophysical behavior are revealed from absorption spectroscopy, steady-state fluorescence, and resonance light scattering studies. Upon addition of aqueous HCl, the efficient formation of H4TPPS2 J-aggregates from the diprotonated form of meso-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4) occurs in [bmim][BF4]-rich media in a manner highly dependent upon the acidity, TPPS concentration, and solvent composition. The unique features of TPPS aggregation in this ionic liquid were elucidated, including the surprising disassembly of J-aggregates at higher aqueous contents, and our results are described qualitatively in terms of the molecular exciton theory. Finally, the potential of this system for the optical sensing of water at a sensitivity below 0.5 wt% is demonstrated. Overall, our findings accentuate how little is known about functional self-assembly within ionic liquids and suggest a number of avenues for exploring this completely untouched research landscape.},
doi = {10.1039/b920500d},
journal = {Physical Chemistry Chemical Physics},
number = 8,
volume = 12,
place = {United States},
year = 2010,
month = 1
}
  • Reduction of the stable Rh/sup III/TPPS (tetrakis(4-sulfonatophenyl)porphyrin) by radiolytic, chemical, or photochemical methods in alkaline aqueous solution results in the formation of Rh/sup II/TPPS which dimerizes to (Rh/sup II/TPPS)/sub 2/ bridged by a Rh-Rh bond. This species is stable toward further reduction in most cases, but pulse radiolysis studies have shown that it can be reduced to the ..pi..-radical anion by the solvated electron. In neutral or acidic solution Rh/sup II/TPPS forms a hydride HRh/sup III/TPPS rather than a dimer although there is some competitive formation of a chlorin. Addition of acid to (Rh/sup II/TPPS)/sub 2/ results in the formationmore » of Rh/sup III/TPPS and HRh/sup III/TPPS while addition of alkali to the hydride results in formation of (Rh/sup II/TPPS)/sub 2/. Alkyl adducts, R-Rh/sup III/TPPS, analogous to the hydride, are formed upon reduction of Rh/sup III/TPPS in the presence of alkyl chlorides. 30 references, 6 figures.« less
  • The reactions of Co/sup II/TPPS (TPPS = tetrakis(4-sulfonatophenyl)porphyrin) with alkyl and hydroxyalkyl radicals have been studied by pulse radiolysis. The alkyl radicals undergo axial addition with rate constants of (1.2-1.9) X 10/sup 9/ M/sup -1/ s/sup -1/ to form R-Co/sup III/TPPS complexes which either are stable (R = CH/sub 3/) or undergo decomposition (R = CH(CH/sub 3/)/sub 2/) to Co/sup I/TPPS and an olefin via a ..beta..-proton elimination mechanism (k/sub 1/ = 0.3 s/sup -1/ at pH 8 and 3 s/sup -1/ at pH 13). The hydroxyalkyl radicals also form R-Co/sup III/TPPS with rate constants of (1.1-1.2) X 10/sup 9/more » M/sup -1/ s/sup -1/. These adducts undergo heterolytic cleavage of the cobalt-carbon bond to form Co/sup I/TPPS and a carbonyl compound, with rate constants of 3.6 X 10/sup 2/ s/sup -1/ (R = CH/sub 2/OH) and 6.2 X 10/sup 3/ s/sup -1/ (R = C(OH)(CH/sub 3/)/sub 2/). The radicals (CH/sub 3/)/sub 2/CO/sup -/ and CO/sub 2//sup -/ reduce Co/sup II/TPPS to Co/sup I/TPPS by an outer-sphere mechanism with rate constants 7 X 10/sup 8/ and 2 X 10/sup 8/ M/sup -1/ s/sup -1/, respectively. Co/sup I/TPPS is oxidized to CH/sub 3/Co/sup III/TPPS by CH/sub 3/I (k/sub 2/ = 3 X 10/sup 5/ M/sup -1/ s/sup -1/) and to Co/sup II/TPPS (probably through intermediate formation of Co/sup III/TPPS) by N/sub 2/O (k/sub 2/ less than or equal to 3 X 10/sup 2/ M/sup -1/ s/sup -1/). The reactivities of the present systems have been compared with those of other models suggested for vitamin B/sub 12/ like cobaloximes, cobalamins, and other macrocyclic Co/sup II/ complexes.« less
  • The reactions of Co/sup II/TPPS (TPPS = tetrakis(4-sulfonatophenyl)prophyrin) with alkyl and hydroxyalkyl radicals have been studied by pulse radiolysis. The alkyl radicals undergo axial addition with rate constants of (1.2 to 1.9) x 10/sup 9/ M/sup -1/s/sup -1/ to form R-Co/sup III/TPPS complexes which either are stable (R = CH/sub 3/) or undergo decomposition R = CH(CH/sub 3/)/sub 2/) to Co/sup I/TPPS and an olefin via a ..beta..-proton elimination mechanism (k/sub 1/ = 0.3 s/sup -1/ at pH 8 and 3 s/sup -1/ at pH 13). The hydroxyalkyl radicals also form R-Co/sup III/TPPS with rate constants of (1.1 to 1.2)more » x 10/sup 9/ M/sup -1/ s/sup -1/. These adducts undergo heterolytic cleavage of the cobalt-carbon bond to form Co/sup I/TPPS and a carbonyl compound, with rate constants of 3.6 x 10/sup 2/s/sup -1/ (R = CH/sub 2/OH) and 6.2 x 10/sup 3/ s/sup -1/ (R = C(OH)(CH/sub 3/)/sub 2/). The radicals (CH/sub 3/)/sub 2/CO/sup -/ and CO/sub 2//sup -/ reduce CO/sup II/TPPS to Co/sup I/TPPS by an outer-sphere mechanism with rate constants 7 x 10/sup 8/ and 2 x 10/sup 8/ M/sup -1/ s/sup -1/, respectively. Co/sup I/TPPS is oxidized to CH/sub 3/Co/sup III/TPPS by CH/sub 3/I (k/sub 2/ = 3 x 10/sup 5/ M/sup -1/ s/sup -1/) and to Co/sup II/TPPS (probably through intermediate formation of Co/sup III/TPPS) by N/sub 2/O (k/sub 2/ less than or equal to 3 x 10/sup 2/ M/sup -1/ s/sup -1/). The reactivities of the present systems have been compared with those of other models suggested for vitamin B/sub 12/ like cobaloximes, cobalamins, and other macrocyclic Co/sup II/ complexes. 36 references, 6 figures, 1 table.« less
  • NMR and spectrophotometric evidence for the formation of a 4:1 cyclodextrin-zinc tetrakis(4-sulfonatophenyl)porphyrin (ZnTSPP) (CD-ZnP) complex is reported. Photolysis of CD-ZnP at 422 nm at pH = 12 was found to lead to quantitative formation (99.9%) of 1,2-dihydroxyporphyrin, which exhibits intense absorption bands at 340 and 625 nm and an emission band at 642 nm. At much lower pH the photolysis was found to lead to the efficient formation of isoporphyrin or its hydroxylated form (pK = 6.0), which possesses characteristic absorption bands in the near infrared region. The nonfluorescing isoporphyrin is converted slowly via molecular rearrangement and further hydroxylation intomore » the fluorescing 1,2-dihydroxyporphyrin (k = 1.1 M{sup {minus}1} s{sup {minus}1}). Emission and excitation spectra of the final stable products are reported. OH{sup {sm bullet}} radical also leads to the formation (although inefficient) of 1,2-dihydroxyporphyrin as shown by {gamma}-radiolysis and pulse radiolysis experiments. Pulse radiolysis experiments in the presence of Br{sup {minus}} were carried out as well. Inhibition of the electron transfer from ZnTSPP to the Br{sub 2}{sup {sm bullet}{minus}} radical in cyclodextrin solution was observed and investigated in detail. The photophysical properties of the inclusion complex and of ZnTSPP{sup 2+} were determined by using the time-correlated single-photon-counting technique and the nanosecond laser absorption spectroscopy method. The absorption spectra of ZnTSPP{sup {sm bullet}3+} and ZnTSPP{sup 4+} are also reported.« less
  • The effect of dimerization on the optical spectra of the title compound TPPS and the ESR spectra of its photoexcited triplet state were investigated. Dimerization can be promoted by addition of cations and cation-crown ether complexes. Two distinct dimer species could be identified with ESR. Dimerization produces red shifts of the optical absorption (Q) bands and fluorescence peaks. In addition, the fluorescence intensity is strongly quenched. These results parallel finding reported for a variety of cofacial covalently linked chlorophylls and porphyrins. However, a striking difference exists between the triplet characteristics of the TPPS dimers on the one hand and covalentlymore » linked dimers. The former exhibit a pronounced dimerization-induced reduction in zero-field splitting values. The values of the latter are very similar to those of their monomer precursors. In this respect, the TPPS system mimics changes found in the triplet ESR spectra associated with the transition from chlorophyll monomers (in vitro) to chlorophyll dimers in reaction centers of« less