Stereochemical Stability and Absolute Configuration of Atropisomeric Alkylthioporphyrazines by Dynamic NMR and HPLC Studies and Computational Analysis of HPLC‐ECD Recorded Spectra

Abstract

The conformational and stereodynamic properties of a pyrene‐substituted ethylthioporphyrazine (PzPy), promising as a dye for organic optoelectronic applications and light‐harvesting systems, have been investigated by DFT computations and variable‐temperature NMR and HPLC. In PzPy, rotation around the pyrene–macrocycle bond is hindered and the molecule displays atropisomerism, existing as a pair of enantiomers, thus representing the first chiral alkyl‐porphyrazine to be reported in the literature. The rotational barrier (ΔG‡ ≈ 22.0 kcal mol–1), measured by variable‐temperature HPLC experiments, allows chromatographic separation of the enantiomers on a chiral stationary phase below 0 °C, whereas racemization spontaneously occurs at room temperature. The absolute configurations of the eluted enantiomers were also determined by computational analysis of their electronic circular dichroism spectra. The influence of alkyl chain length and metal complexation on the molecular stereodynamic properties have also been investigated by studying its novel octylthio derivative (PzPy‐octyl) and PdII complex (PdPzPy), respectively. The latter also is the first example of a PdII–alkylthioporphyrazine complex. Given that PzPy has been used in the preparation of hybrid materials with nanocarbons for optoelectronic applications, the presence of an axial chirality element may play a key role in its interaction with semiconducting chiral nanotubes.

Characterization of “Free Base” and Metal Complex Thioalkyl Porphyrazines by Magnetic Circular Dichroism and TDDFT Calculations

“…In fact, they allow ample and facile synthetic modularity, display a wider UV–vis absorption range, promising the development of panchromatic photovoltaic materials and, under some circumstances, can give rise to columnar liquid crystal mesophases. 11 − 15 Very few examples of porphyrazine applications in NLO 16 − 24 and OPV 25 , 26 have been reported, and only very recently some of us have described the potentiality of nonsymmetrically substituted thioalkyl porphyrazines in OPV 27 , 28 and NLO. 29 , 30 For the development of new optoelectronic materials based on the porphyrazine framework, a detailed knowledge of their electronic structure is of utmost importance.…”

Pinofuranoxins A and B, Bioactive Trisubstituted Furanones Produced by the Invasive Pathogen Diplodia sapinea

“…Once the structures of (+)- 1 and (+)- 2 had been determined, the absolute configuration (AC) of both compounds were assigned by computational analysis of their electronic circular dichroism (ECD) spectra, 11 an approach that has proven to be particularly reliable and straightforward for the AC assignment in solution of complex chiral compounds 12 including natural products. 13 , 14 Accordingly, the ECD spectra of 1 and 2 were recorded in MeCN in the 200–340 nm range.…”

Computational Approaches and Use of Chiroptical Probes in the Absolute Configuration Assignment to Natural Products by ECD Spectroscopy: A 1,2,3-Trihydroxy-p-menthane as a Case Study

“…At first, AC assignment to triol (-)-1 was attempted by comparison of the experimental and the TDDFT-computed ECD spectra, following a reliable and straightforward approach employed for a number of chiral compounds [54], including natural products [55,56]. Accordingly, the UV and ECD spectra of (-)-1 were recorded in acetonitrile in the 180-300 nm range.…”