Structure and Conformation of Photosynthetic Pigments and Related Compounds. 12. A Crystallographic Analysis of Porphyrin‐quinones and Their Precursors

Abstract

Abstract. A comprehensive crystallographic analysis of 10 porphyrin quinone precursors (dimethoxybenzene derivatives), and six porphyrin quinones has been performed. The free bases and zinc(II) complexes of the porphyrin quinones are of the 5,10,15‐triaryl/alkyl‐20‐quinone‐porphyrin type and carry various bridging and quinone units. The structural and conformational parameters were determined for all compounds; the donor‐acceptor separation distances range from 6.3 to 10.9 Å. Knowledge of these data is a prerequisite for a detailed interpretation of theoretical and spectroscopic studies on such systems. Despite the obvious influence of the type and geometry of the bridging unit and quinone on the spatial arrangement of the donor and acceptor components, a large variety of different packing arrangements in the crystal were observed. These include π stacking, aggregate formation and axial ligation in the zinc(II) porphyrins. The latter often utilized the quinone (or dimethoxy) oxygen atoms for coordination to zinc(II) centers leading to porphyrin quinone dimers and even polymers.

Structure and Conformation of Photosynthetic Pigments and Related Compounds. 13. Identification of Localized Vibrational Modes in Chlorophyll A Derivatives

“…Small, but real spectral differences were found between the 10-epimers. This investigation continues our earlier studies on the conformation and structure of photosynthetic pigments 15 and complements related studies on the mass spectrometric analysis of ring V chlorophyll derivatives. 16…”

Porphyrin-anthraquinone dyads: Synthesis, spectroscopy and photochemistry

“…These changes could be interpreted in terms of ligation of the anthraquinone carbonyl group (C=O) with the central zinc(II) porphyrin. 37,38 This would bring the protons present on the anthraquinone subunit into the shielding region of the ring current of the coordinated porphyrin. 39 Maximum absorbance wavelengths (λ max ) and molar extinction coefficient (log ε) values of the three new dyads and of their constituent individual components (i.e.…”

Towards Triptycene Functionalization and Triptycene-linked Porphyrin Arrays

“…The structure of 5 was solved with one molecule in the asymmetric unit with the bridgehead substituents being almost 180° to each other ( Figure 2, for labelling see Figure S33 in the supporting information). Unlike the unsubstituted triptycene 1 crystal structure which exhibits a high degree of C-H•••π interactions between the aromatic rings [37], there is a high degree of interdigitation between the aromatic rings of the triptycene unit ( Figure 2b) akin to some triptycene-quinones [38]. This is due to two of the (Figure 2c).…”