Helicity Modulation in NIR‐Absorbing Porphyrin‐Ryleneimides

• Published in: Angewandte Chemie Vol. 134; no. 18
• Main Authors: Balahoju, Shivaprasad Achary, Maurya, Yogesh Kumar, Chmielewski, Piotr J., Lis, Tadeusz, Kondratowicz, Mateusz, Cybińska, Joanna, Stępień, Marcin
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 25.04.2022
• Subjects: Cadmium; Chemistry; Chirality; Chromophores; Coordination Chemistry; Coordination compounds; Helicity; Mathematical analysis; Metal Complexes; Metal ions; Porphyrins; Propellers; Stereochemistry; Water chemistry
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202200781

Peripheral substitution of a π‐extended porphyrin with bulky groups produces a curved chromophore with four helical stereogenic units. The curvature and stereochemistry of such porphyrins can be controlled by varying the substituents, coordinated metal ions, and apical ligands. In particular, when the achiral saddle‐shaped free bases are treated with large metal ions, i.e., CdII or HgII, the resulting complexes convert to chiral propeller‐like configurations. X‐ray diffraction analyses show that apical coordination of a water molecule is sufficient to induce a notable bowl‐like distortion of the cadmium complex, which however retains its chiral structure. For phenyl‐ and tolyl‐substituted derivatives, the conversion is thermodynamically controlled, whereas complexes bearing bulky 4‐(tert‐butyl)phenyl groups transform into their chiral forms upon heating. In the latter case, the chiral Hg porphyrin was converted into the corresponding free base and other metal complexes without any loss of configurational purity, ultimately providing access to stable, enantiopure porphyrin propellers. Stereochemistry and curvature of porphyrin‐based nanographenes change in response to coordination of metal ions and heat. By judicious choice of ionic radii, peripheral substituents and apical ligands, it is possible to control the thermodynamics and kinetics of isomerization, to achieve conversion between achiral and chiral structures.