Sequence, Stoichiometry, and Dimensionality Control in Porphyrin/Bis‐calix[4]arene Self‐Assemblies in Aqueous Solution

Abstract

The use of a water-soluble octacationic bis-calix[4]arene with divergent cavities (BC(4)) as a templating agent for the assembly of a tetraanionic porphyrin (CuTPPS) has allowed the noncovalent synthesis of 2D or 3D multiporphyrin assemblies. Self-assembly of CuTPPS and BC(4) molecules proceeded under hierarchical control in a stepwise fashion to yield discrete and isolable supramolecular nanostructures containing up to 33 molecular elements (i.e., the CuTPPS/BC(4) 17:16 assembly, obtained in less than three hours). The formation of these species could be conveniently monitored by means of UV/Vis spectroscopy by following the absorbance of the Soret band at 412 nm. In particular, the attainment of the pivotal CuTPPS/BC(4) 5:4 species with a cruciform structure, as the key fork-point intermediate for the subsequent formation of the higher 2D and 3D assemblies, has been demonstrated by light-scattering studies and by an unequivocal synthesis of mixed-porphyrin/calixarene 5:4 species involving the use of two different types of metallated porphyrins, namely CuTPPS and MnTPPS. The remarkable stability of these assemblies permits a stepwise synthesis that makes it possible to choose the desired porphyrin sequence.

Selected applications of calixarene derivatives

“…21 Besides classical calixarenes, also calixarenes containing modified meso bridges are known, 22 they are calixradialenes, 23 ketocalixarenes 24 and homocalixarenes. 25,26 The noncovalent calixarene assemblies with porphyrins [27][28][29] are recently the theme of a large amount of reports. 30 …”

Amino Surface‐Functionalized Tris(calix[4]arene) Dendrons with Rigid C3‐Symmetric Propeller Cores

“…13 C NMR spectra were acquired with the attached proton test (APT) technique. ESI MS spectra were recorded with a Finnigan LCQ-deca XP ion trap electrospray mass spectrometer (Bremen, Germany).…”

“…[12] In the context of a long-term project aimed at investigating the design, structure, and properties of new hybrid materials generated from the noncovalent assembly of tetracationic or tetraanionic porphyrins with appropriate complementary charged multi-calix[4]arene components in water solution, we have already shown that the templating action of a centrosymmetric water-soluble octacationic homoditopic bis-calix[4]arene with divergent cone cavities on a tetraanionic metallated porphyrin makes it possible to exert control over the noncovalent synthesis of dendrimeric calix[4]arene/porphyrin assemblies by predetermining their sequence, stoichiometry, and dimensionality (2D or 3D). [13] On the other hand, C 3 -symmetric building blocks have been widely employed to prepare complex target molecules that have found application in areas as diverse as analytical chemistry, [14] molecular recognition, [15] materials science, [16] and supramolecular chemistry. [17] Furthermore, they have also been used as central cores for the design of dendrimeric frameworks with increased diversity.…”

Long‐Range Chiral Induction by a Fully Noncovalent Approach in Supramolecular Porphyrin–Calixarene Assemblies

“…Specifically, the titration of an aqueous solution (pH 2) of biscalixarene BC4 ( BC4 is known to exist as a fully‐protonated cationic species at pH 2; see ref. ). with increasing amounts of MnTPPS produced, with respect to a MnTPPS solution of equivalent concentration, a hypochromic effect (as well as a broadening, see the inset to Figure S1) on the porphyrin Soret band and, in turn, the related plot of the absorption maxima (Figure S2), revealed the presence of a series break points , consistent with the formation of the desired 1:4‐( MnTPPS / BC4 ) central complex and the following 2:4‐, 3:4‐, and 4:4‐ and 5:4‐( MnTPPS / BC4 ) complexes.…”

“…Bearing in mind our earlier findings on the electronic communication between outer CuTPPS and central MnTPPS porphyrins of BC4 ‐containing multi‐porphyrin aggregates, we then decided to test the ability of chiral calixarene C4 to deliver chiral information across long‐distance, namely from the periphery of the 1:4:4‐( MnTPPS / BC4 / CuTPPS ) assembly to its central MnTPPS core. Stepwise addition of 12 equivalents of ( R )‐ C4 (or ( S )‐ C4 ) to a solution containing the preformed 1:4:4‐( MnTPPS / BC4 / CuTPPS ) assembly gave rise to dichroic signals in the Soret region of CuTPPS but also produced a perturbation in the MnTPPS absorption region (Figure and Figure S5), thus confirming a long‐distance chiral induction process.…”