Issue 16, 2014

Aggregation of a model porphyrin within poly(ethylene glycol) (PEG): effect of water, PEG molecular weight, ionic liquids, salts, and temperature

Abstract

Understanding molecular aggregation within environmentally-benign media is of utmost importance. Aggregation of a common porphyrin, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TSPP), dissolved in media composed of poly(ethylene glycols) (PEGs) up to an average molecular weight (MW) of 8000 as major components, is investigated. J-aggregates of TSPP are well-manifested via the bathochromically-shifted UV-vis absorbance band of TSPP. As media, 10 wt% water-added PEGs at pH 1 show excellent efficiency for TSPP J-aggregation. The J-aggregation efficiency increases as the PEG MW is increased and it is found to be the maximum for the medium constituted of PEG3000. Once formed, some of the J-aggregates decay back to the diprotonated form via pseudo-first order kinetics. Addition of salts NaCl and NaBF4 and ionic liquids [bmim][PF6], [bmim][Tf2N], [bmim][BF4], and [bmim][OTf] [bmim = 1-butyl-3-methylimidazolium, PF6 = hexafluorophosphate, Tf2N = bis(trifluoromethylsulfonyl)imide, BF4 = tetrafluoroborate, and OTf = trifluoromethanesulfonate], respectively, to TSPP dissolved in 10 wt% water added PEGs at pH 1 results in increased J-aggregation efficiency. Ionic liquids are found to protect porphyrin J-aggregates from decaying to their diprotonated form. Increasing temperature from ambient to 90 °C results in decreased J-aggregation efficiency of TSPP in the presence of salts NaCl and NaBF4, respectively; concentration of J-aggregates does not change much with temperature when an ionic liquid as an additive is present in the medium. The polymer chain length and electrostatic interactions appear to play a major role in porphyrin J-aggregation efficiency and kinetics within water-added acidic mixtures of PEG.

Graphical abstract: Aggregation of a model porphyrin within poly(ethylene glycol) (PEG): effect of water, PEG molecular weight, ionic liquids, salts, and temperature

Supplementary files

Article information

Article type
Paper
Submitted
09 Jan 2014
Accepted
18 Feb 2014
First published
19 Feb 2014

Phys. Chem. Chem. Phys., 2014,16, 7263-7273

Author version available

Aggregation of a model porphyrin within poly(ethylene glycol) (PEG): effect of water, PEG molecular weight, ionic liquids, salts, and temperature

R. Rai, V. Kumar and S. Pandey, Phys. Chem. Chem. Phys., 2014, 16, 7263 DOI: 10.1039/C4CP00103F

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