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.

Synthesis of a poly(ethylene glycol) galloyl sensitizer tip for an ’all‐in‐one' photodynamic device

“…TriPEG‐galloyl pheophorbide and triPEG‐chlorin (entries 2 and 4) led to a lipophilic deamplification by 1.9 log units compared to unsubstituted sensitizers, respectively (entries 1 and 3). Lower log P values of PEGylated compounds would be expected, where their curling onto the porphyrin ring inhibits aggregation due to π–π stacking forces . The reduced log P of the PEGylated pheophorbide versus native hydrophobic pheophorbide‐ a will make the former more accessible and less prone to aggregating, to potentially address the challenge in sterilization of surgical margins.…”

“…Lower log P values of PEGylated compounds would be expected, where A. A. Ghogare and A. Greer: Synthesis of a poly(ethylene glycol) galloyl sensitizer tip their curling onto the porphyrin ring inhibits aggregation due to π-π stacking forces [60][61][62][63][64][65][66]. The reduced log P of the PEGylated pheophorbide versus native hydrophobic pheophorbide-a will make the former more accessible and less prone to aggregating, to potentially address the challenge in sterilization of surgical margins.…”

Applications of Ionic Liquids in Spectroscopy

“…[26][27][28][29][30][31][32][33][34][35][36] Suggestion that solvated electrons in ionic liquids produce absorption spectra is corroborated by a report where it is found that the solvated electron exhibits an absorption spectrum peaking in the 1000-1400 nm region and a second absorption band peaking in the UV region. [26][27][28][29][30][31][32][33][34][35][36] Suggestion that solvated electrons in ionic liquids produce absorption spectra is corroborated by a report where it is found that the solvated electron exhibits an absorption spectrum peaking in the 1000-1400 nm region and a second absorption band peaking in the UV region.…”

“…29 , respectively, to TSPP dissolved in 10 wt% water added PEGs at pH 1 results in increased J-aggregation efficiency. 29 , respectively, to TSPP dissolved in 10 wt% water added PEGs at pH 1 results in increased J-aggregation efficiency.…”

Interplay of monomers, dimers and J-aggregates of thiamonomethinecyanine dye with PEDOT and PSS in the dye–PEDOT:PSS composite system

“…Biswas et al [18] explained polymer template enhanced J-aggregation of porphyrin dyes by ionic interactions of the cationic side chains of the functionalized polymer under acidic conditions with the negatively charged sulfonate groups of the porphyrins. Rai et al [19] have found that poly(ethylene glycol) chain length and electrostatic interactions play a major role in porphyrin J-aggregation efficiency.…”