Journal of Physical Chemistry A, Vol.118, No.6, 1038-1046, 2014
Structure, Electronic States, and Anion-Binding Properties of Cyclo[4]naphthobipyrroles
Three octaalkyl-substituted cyclo[4]-naphthobipyrroles, studied in solution in the form of their sulfates, reveal absorption and magnetic circular dichroism (MCD) spectra very similar to those of the parent cyclo[8]pyrrole. A unique feature of these systems is a strong absorption in the near IR region. The analysis of MCD patterns based on a perimeter model reveals a hard-chromophore character of cyclo[4]naphthobipyrroles, i.e., Delta HOMO << Delta LUMO. Comparison of Raman spectra obtained for crystalline samples and solutions, combined with the analysis of absorption and MCD spectra based on quantum chemical calculations reveals that cyclo[4]naphthobipyrroles exist in solutions as undissociated sulfates of the doubly protonated forms.