Indaphyrins and Indachlorins: Optical and Chiroptical Properties of a Family of Helimeric Porphyrinoids

Abstract

Indaphyrins and indachlorins possess large chiral porphyrinoid π‐systems with particularly long‐wavelength absorption properties. All indaphyrin derivatives, including the indaphyrin MII complexes (M = NiII, CuII, ZnII, and PtII), adopt strongly ruffled conformations incorporating a helimeric twist, thus forming two stereochemically stable helimeric enantiomers. Their degree of ruffling is modulated by the coordination to metal ions or pyrrole ring modifications. Resolution of the racemic mixtures of the helimers of all derivatives was achieved by HPLC on a chiral phase and their absolute stereostructures were assigned. The much altered UV/Vis spectra of the indaphyrin derivatives, when compared to those of porphyrins, were rationalized using excited state calculations. The conformational stability of the conformers toward thermally induced racemization was also shown. The report forms the basis for future applications that exploit the chiral properties of the chromophores.

Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

“…It is noteworthy that in all cases described by Pecul and Ruud and Crawford et al., RI‐CC2 or EOM‐CCSD calculations always agreed with TD‐DFT on the predicted sign of CPL bands . The present inconsistency between TD‐DFT and coupled‐cluster calculations is, to the best of our knowledge, unprecedented in the context of CPL, whereas in the context of ECD calculations some discrepancies between TD‐DFT and CC2 have been reported, mostly related to transitions with large charge‐transfer character …”

Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm

“…In a separate contribution we demonstrated that the π‐system of free base and metalated indaphyrins show the hallmarks of a porphyrin‐type π‐system, as expressed in the relative order of the frontier orbitals according to the Gouterman four‐orbital model of porphyrinoid spectra 23. We therefore understand them as porphyrin analogues, irrespective of some chlorin‐like characteristics (see regioselectivity of the dihydroxylation).…”

“…The crystal structure of the starting indaphyrin 9 shows that it is ruffled, expressing helimeric chirality (Figures 1 and 3; for a detailed discussion of the conformation of 9 and its derivatives, see below). Assuming this conformation is also maintained in the solution state (a supposition supported by the ability to separate indaphyrin into its enantiomers by chiral HPLC),23 it provides the key to understanding the 1 H NMR signal pattern. The vic ‐ cis ‐diol moiety breaks the two‐fold rotational symmetry of the ruffled macrocycle, rendering all protons diastereotopic (Figure 1).…”

“…To date, the conformation of the parent free base indaphyrin 9 has only been computed 22b. 23 However, we were now able to grow suitable crystals for analysis by X‐ray diffractometry. Its conformation verifies the predicted strongly ruffled conformation of 9 (Figure 3), though depending on the level of computation, the degree of ruffling was either over‐ or underestimated, which may be an indication of the high conformational flexibility of the molecule 22b.…”

“…This conformation and the π‐extended chromophore rationalize the redshifted optical spectra of the indaphyrins, which clearly fall outside of the standard porphyrin/chlorin‐type spectral categories. The indaphyrin and indachlorin UV/Vis spectra are described below and are rationalized elsewhere 23…”