Chiral tetrakis(4-carboxyphenyl) porphyrin aggregates induced by enantiomeric dibenzoyl tartaric acids at the air-water interface

Enantiomeric dibenzoyl tartaric acid (DBTarA)-induced formation of chiral tetrakis(4-carboxyphenyl)porphyrin (TCPP) aggregates have been investigated in solutions and at the air-water interface. Surface pressure-area isotherms of the monolayers, UV-vis, and infrared spectra, as well as X-ray photoelectron spectra of the transferred Langmuir-Blodgett (LB) films, indicated that, though the small DBTarA molecules had difficulty forming insoluble monolayers at the interfaces, they could insert themselves in the matrix of porphyrins to form TCPP-DBTarA mixed monolayers and LB films. The inorganic salt of CdCl2 in the subphase could stabilize the mixed monolayers due to formation of the coordination bond between Cd(II) ions and carboxylic acid substituents of TCPP and DBTarA. Mirror-imaged circular dichroism spectra were recorded with two signals centered at about 230-250 and 400-450 nm; the former indicated that chirality of the DBTarA remained in the LB films while the latter (corresponding to the Soret absorption band of porphyrins) indicated that the co-existing DBTarA could induce the formation of supramolecular chirality in the porphyrins. It was revealed that pure TCPP formed dot-like aggregates while its mixtures with DBTarA formed irregular nanowires on the CdCl2 subphase surface, a phenomenon which may be attributed to the fact that the coordination bond of Cd-OOC connects TCPP and DBTarA molecules to form larger one-dimensional ternary molecular assemblies. (C) 2014 Elsevier B.V. All rights reserved.