Chiroptical Properties of Acridino-18-Crown-6 Ligands and Their Complexes with Chiral and Achiral Protonated Primary (Aralkyl) Amine Guest Molecules

This paper reports CD spectroscopic studies on acridino-18-crown-6 ligands ( R , R )- 2 and 2a (see Figure 1), and their complexes with the enantiomers of -(1-naphthyl)ethylamine hydrogenperchlorate (1-NEA), 1-phenylethylamine hydrogenperchlorate (PEA) and -(2-naphthyl)ethylamine hydrogenperchlorate (2-NEA), and also with the achiral guests (1-naphthyl)methylamine hydrogenperchlorate (1-NMA), benzylamine hydrogenperchlorate (BA), methylamine hydrogenperchlorate (MA) and 1-methylnaphthalene (1-MN). The general feature of the CD spectra of complexes of ( R , R )- 2 with MA, BA, ( R )- and ( S )-PEA is the replacement of the oppositely signed 1 B b doublet of the host by one positive band near 265 nm. The CD spectra of the heterochiral and homochiral complexes of phenazino and acridino hosts ( R,R )- 1 , 1a , ( R , R )- 2 and 2a with ( R )- and ( S )-1-NEA and 1-NMA are governed by exciton interaction. Surprisingly, the heterochial [( R , R )/( S )] complexes of the structural isomeric 2-NEA gave rise to a positive couplet in contrast to the negative couplet measured in the spectrum of the heterochiral [( R,R )/( S )] complexes of 1-NEA.

Keywords:

• Chiral Crown-ethers
• Circular Dichroism (CD)
• Enantiomeric Recognition
• Exciton Chirality
• Supramolecular Complexes