Recognition of Chiral Catechols Using Oxo−Titanium Phthalocyanine

Abstract

Oxo-titanium phthalocyanine (TiOPc) derivatives of catechin and hematoxylin (natural ortho-diol type chiral compounds) have been prepared and characterized by spectral and chromatographic techniques. It is demonstrated that the TiOPc unit is an excellent template for chiral recognition through its isolated Q-transitions. The formation of a helical dimeric complex with hematoxylin induces strong CD-activity in the Q-band region. Ab initio geometry optimizations were combined with a Kuhn-Kirkwood coupled-oscillator mechanism to obtain the absolute configuration of hematoxylin. In addition, it is shown that the described chiroptical recognition method is sensitive to slight conformational changes.

Supramolecular Chirality in Porphyrin Chemistry

“…Different structural types of rigidly linked bridges have also been successfully employed, as shown in the following chiral bis-porphyrinoids. Hence, the hematoxylin fragment was applied to fix a pair of phthalocyanines in 22 to produce the corresponding chiral orientation (Figure 8) [33]. The chiroptical outcome consisted of an intense negative-to-positive bisignate CD signal in the Q-band region and several weak signals in the Soret band area as a result of the excitonic interaction between two porphyrinoids.…”

Spectroscopic and Theoretical Studies of Optically Active Porphyrin Dimers: A System Uninterpretable by Exciton Coupling Theory

“…[1][2][3] One can assign the sense of chiral arrangement of the relevant chromophores from the sign of derivative-shaped CD signals generated by excitonic interactions between the transition electric dipole moments of two chromophores in a chiral environment. [4][5][6][7] Although the excitoncoupled CD method has succeeded in determining the helical structures of many organic molecules, the application of this method is limited for independent chromophoric systems from a theoretical point of view; [1] the application of exciton coupling models requires spatially separated chromophoric units. [8] Therefore, chiral systems such as helicenes are not suitable for application of this method.…”

“…[4][5][6] The electronic excited states of a meso-meso b-b doubly linked bis-porphyrin are comprehensively investigated by measuring its circular dichroism (CD) and magnetic circular dichroism (MCD) spectra. The observed spectroscopic properties are rationalized by DFT calculations.…”

Phthalocyanine, Porphyrin, Cyclodextrin, and Polymer Systems Suitable for Studying by Circular Dichroism, Magnetic Circular Dichroism, and/or Electrochemistry

“…This was possible since hematoxylin contains a plurality of catechol units and TiOPc was found to react with catechol to form a catechol coordinated (as an axial ligand) Pc. 54 With respect to the chemical structure of hematoxylin, it was known beforehand from NMR spectroscopy that it takes a cis type structure. 55 Of the conceivable absolute structure [(6aS,11bR) form], the two structures shown in Figure 26 (top) are possible, depending on the orientation of the CH 2 -carbon of the pyran ring in the central moiety of hematoxylin (the structures to the left and right are distinguished as A-and B-structure, respectively).…”