Supramolecular Chirogenesis in Bis-Porphyrin: Crystallographic Structure and CD Spectra for a Complex with a Chiral Guanidine Derivative

Abstract

The complexation of (3aR,7aR)-N-(3,5-bis(trifluoromethyl)phenyl)octahydro-2H-benzo[d]imidazol-2-imine (BTI), as a guest, to ethane-bridged bis(zinc octaethylporphyrin), bis(ZnOEP), as a host, has been studied by means of ultraviolet-visible (UV-Vis) and circular dichroism (CD) absorption spectroscopies, single crystal X-ray diffraction, and computational simulation. The formation of 1:2 host-guest complex was established by X-ray diffraction and UV-Vis titration studies. Two guest BTI molecules are located at the opposite sides of two porphyrin subunits of bis(ZnOEP) host, which is resting in the anti-conformation. The complexation of BTI molecules proceed via coordination of the imine nitrogens to the zinc ions of each porphyrin subunit of the host. Such supramolecular organization of the complex results in a screw arrangement of the two porphyrin subunits, inducing a strong CD signal in the Soret (B) band region. The corresponding DFT computational studies are in a good agreement with the experimental results and prove the presence of 1:2 host-guest complex as the major component in the solution (97.7%), but its optimized geometry differs from that observed in the solid-state. The UV-Vis and CD spectra simulated by using the solution-state geometry and the TD-DFT/ωB97X-D/cc-pVDZ + SMD (CH2Cl2) level of theory reproduced the experimentally obtained UV-Vis and CD spectra and confirmed the difference between the solid-state and solution structures. Moreover, it was shown that CD spectrum is very sensitive to the spatial arrangement of porphyrin subunits.

Application of TD-DFT Theory to Studying Porphyrinoid-Based Photosensitizers for Photodynamic Therapy: A Review

“…Most of the DFT calculations for PDT use the second approach. The most popular is the polarized continuum model (PCM), which has several variants, such as dielectric D-PCM and the conductor-like polarized continuum model (C-PCM), also called COSMO [ 97 , 98 ]—see, e.g., [ 87 , 99 , 100 ].…”

Thiourea Organocatalysts as Emerging Chiral Pollutants: En Route to Porphyrin-Based (Chir)Optical Sensing

“…The (chir)optical outcome is clearly specific for a certain host-guest combination, with respect to both the amplitude and sign of observed Cotton effects (CE). Such variability is not unexpected in the view of the complex origin of net CD signal [26,69,101,[118][119][120]. Enantiomers of compound 1a display CD signal in the far-UV region with λ max of 253 nm and 308 nm and intensities of 15 M −1 •cm −1 and 28 M −1 •cm −1 , respectively (see Figure S86 in the Supplementary Materials).…”

Self-Assembly of Chiral Cyclohexanohemicucurbit[n]urils with Bis(Zn Porphyrin): Size, Shape, and Time-Dependent Binding

“…The amount was rationalized based on the shape of UV-vis titration binding isotherms (seeming saturation in the case of cycHC [8]) and mole fractions based on the obtained association constants for cycHC [6]. We examined previously obtained crystal structures of bis-ZnOEP [51][52][53] and of cycHC[n] with ZnTPP [36] for their similarity to herein presented complexes. All distances were measured between the centers of corresponding atoms, and the van der Waals radius was then added.…”