A General Method for Constructing Optically Active Supramolecular Assemblies from Intrinsically Achiral Water‐Insoluble Free‐Base Porphyrins

Abstract

We have developed a general method to construct optically active porphyrin supramolecular assemblies by using a simple air-water interfacial assembly process. The method involved the in situ diprotonation of the free-base porphyrins at the air-water interface and subsequent assembly under compression. We showed that two intrinsically achiral water-insoluble free-base porphyrin derivatives, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (H(2)OEP) and 5,10,15,20-tetra-p-tolyl-21H,23H-porphine (H(2)TPPMe), could be diprotonated when spread onto a 2.4 M hydrochloric acid solution surface, and the Langmuir-Schaefer (LS) films fabricated from the subphase exhibited strong circular dichroism (CD) absorption, whereas those fabricated from pure Milli-Q water subphase did not. The experimental data suggested that the helical stacking of the achiral porphyrin building blocks was responsible for the supramolecular chirality of the assemblies. Interestingly, such a method was successfully applied to a series of other intrinsically achiral free-base porphyrins such as 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (H(2)TPPOMe), 5,10,15,20-tetraphenyl-21H,23H-porphine (H(2)TPP), 5,10,15,20-tetrakis(4-(allyloxy)phenyl)-21H,23H-porphine (H(2)TPPOA), and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine (H(2)TPPDOMe). A possible mechanism has been proposed. The method provides a facile way to obtain optically active porphyrin supramolecular assemblies by using intrinsically achiral water-insoluble free-base porphyrin derivatives.

Interfacial organization of achiral porphyrins via unidirectional compression: a general method for chiroptical porphyrin assemblies of selected chirality

“…24 On the other hand, as shown in Fig. S4 (ESI †), the UV-Vis spectra of our present assemblies are also similar to those of the corresponding samples formulated by the traditional bilateral compression geometry.…”

“…S4 (ESI †), the UV-Vis spectra of our present assemblies are also similar to those of the corresponding samples formulated by the traditional bilateral compression geometry. 24 These results indicate that the chiroptical signals of our present samples are attributed to the molecular packing of the assemblies. 24 Moreover, it has been suggested that the authenticity of the observed macroscopic chirality through the CD measurement could not be exclusively determined for the solid state samples or for a stirring system, because the detected CD spectra are often contaminated by the LD artifact, which usually originate from the macroscopic anisotropies of a sample.…”

“…24 These results indicate that the chiroptical signals of our present samples are attributed to the molecular packing of the assemblies. 24 Moreover, it has been suggested that the authenticity of the observed macroscopic chirality through the CD measurement could not be exclusively determined for the solid state samples or for a stirring system, because the detected CD spectra are often contaminated by the LD artifact, which usually originate from the macroscopic anisotropies of a sample. [35][36][37][38][39] In practice, for the measurement of CD spectra of LS films, the sample was placed perpendicular to the light path and at the same time was rotated continuously within the substrate plane using a custom build rotator to avoid the polarization-dependent reflections and eliminate the possible angle dependence of the CD signal.…”

Controllable growth of one-dimensional chiral nanostructures from an achiral molecule

“…With respect to one-dimensional chiral nanostructures, great advances have been achieved in the past few years. However, building chiral nano-/micrometer-sized materials with interesting properties from an achiral molecule [30,31] is of great difficulty. In our report, we studied the self-assembly of organic molecule of thioxanthone-anthracene (TX-A) (Fig.…”

Aggregation and supramolecular chirality of achiral amphiphilic metalloporphyrins

“…In principle, the chirality could either be exhibited within molecular level or be shown in the level of supramolecular assemblies [8]. However, the constructions of chiral porphyrin assemblies from achiral porphyrins are always extremely challenging, and were only carried out in a few particular cases [9][10][11][12].…”