J-aggregates of diprotonated tetrakis(4-sulfonatophenyl)porphyrin induced by ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate.

The J-aggregation behavior of diprotonated tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4(2-)) in aqueous solution in the presence of the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) was investigated in detail using UV-vis absorption spectroscopy, fluorescence spectroscopy, resonance light scattering (RLS) spectroscopy, Raman spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. With the addition of bmimBF4, increasing peaks appeared at a wavelength of 490 nm in the absorption spectra to account for the formation of H 2TPPS4(2-) J-aggregates. In addition, the experimental results also showed decreased fluorescence emission, enhanced RLS signals, intensified Raman scattering peaks, and the disappearance of NMR signals to further indicate that porphyrin J-aggregates exist in the studied system. NMR shifts of bmimBF 4 toward high field occurred corresponding to H2, H4, and H5 in the cationic imidazolium ring (bmim+), suggesting that bmim+ enters the magnetic shielding domain of the anionic phenyl sulfonate ion owing to the association process between the "large" cation and anion. Additionally, the fact that the absorption spectral shifts occurred in the nonprotonated porphyrin TPPS4(4-) further indicates the existence of the ion association effect of bmim+, which functions as an important factor in porphyrin aggregation.