Induced Optical Chirality of Porphyrin J-Aggregates with 2-Alkyl Alcohol in a Microemulsion System

Abstract

The J-aggregates of the diprotonated tetraphenylporphin formed in the o/w microemulsions including 2-alkyl alcohol, Triton X-100, toluene, and sulfuric acid, exhibited an induced circular dichroism (ICD) spectra corresponding to the chirality of the alcohol. The ICD intensity remarkably depended on the concentrations of Triton X-100 and sulfuric acid as well as 2-alkyl alcohol. The results suggested the nonstoichiometric formation of the chiral conformation of the nano-J-aggregates in the microemulsion droplets.

Chiral Recognition of 2-Alkylalcohols with Magnetic Circular Dichroism Measurement of Porphyrin J-Aggregate on Silica Gel Plate

“…It is noted that the ICD intensity in the Q-band region is about 1.8 times higher than that in the Soret band region. This is a different feature from the observation in the microemulsion systems, where the ICD intensity in the Soret band region was 4 times larger than that in the Q-band region . It may be related to the fact that the dispersion of light in the silica gel is greater in the shorter wavelength and the ellipticity in the shorter wavelength is somewhat reduced.…”

“…However, for the chiroptical detection of molecules having no significant absorption bands, various molecular probes, which exhibit induced circular dichroism (ICD) spectra, have been developed. Especially, porphyrin dimers have been extensively studied as chiral probes. − Porphyrin aggregates also have been reported as a powerful probe of ICD spectra for UV, visible nonabsorbing chiral molecules such as alkylalcohols. , Tetraphenylporphyrin (H 2 TPP, Figure ) has been used as the chiral recognition reagent of 2-alkylalcohol after forming J-aggregate of the diprotonated form (H 4 TPP 2+ ) at the liquid–liquid interface and in the oil-in-water microemulsions . In the event of the formation of the nano-J-aggregate, the chiral molecules were thought to be incorporated between the aggregates and generate helical conformation of the J-aggregates.…”

“…1−4 Porphyrin aggregates also have been reported as a powerful probe of ICD spectra for UV, visible nonabsorbing chiral molecules such as alkylalcohols. 5,6 Tetraphenylporphyrin (H 2 TPP, Figure 1) has been used as the chiral recognition reagent of 2-alkylalcohol after forming Jaggregate of the diprotonated form (H 4 TPP 2+ ) at the liquid− liquid interface 5 and in the oil-in-water microemulsions. 6 In the event of the formation of the nano-J-aggregate, the chiral molecules were thought to be incorporated between the aggregates and generate helical conformation of the Jaggregates.…”

“…5,6 Tetraphenylporphyrin (H 2 TPP, Figure 1) has been used as the chiral recognition reagent of 2-alkylalcohol after forming Jaggregate of the diprotonated form (H 4 TPP 2+ ) at the liquid− liquid interface 5 and in the oil-in-water microemulsions. 6 In the event of the formation of the nano-J-aggregate, the chiral molecules were thought to be incorporated between the aggregates and generate helical conformation of the Jaggregates. Significant ICD bands were observed around the Soret band and Q-band of the porphyrin.…”

“…This is a different feature from the observation in the microemulsion systems, where the ICD intensity in the Soret band region was 4 times larger than that in the Q-band region. 6 It may be related to the fact that the dispersion of light in the silica gel is greater in the shorter wavelength and the ellipticity in the shorter wavelength is somewhat reduced. Furthermore, in the o/w microemulsion systems, the formation of the Jaggregate was only 20% and other porphyrin was left solubilized as the monomer of the diprotonated form, H 4 TPP 2+ , which showed the absorption maximum at 438 nm (Figure S-2).…”