2-(2′-Pyridyl)pyrroles: Part I. Structure and energetics of pyridylpyrroles, their dimers, complexes and excited states

Structural and energetic evaluations of substituted 2-(2′-pyridyl) pyrroles were performed through a combination of computational and experimental methods. In conjunction with experimental absorbance and fluorescence studies, the data were analyzed with respect to hydrogen bonding ability, complex formation with alcohols, dimerization, excited state behavior, and potential for proton transfer. Experimental and theoretical evidence show the importance of the pyrrole substituent groups in both structural and spectral properties of the molecules and their complexes. Low temperature NMR experiments and full solution phase DFT optimizations support the formation of a cyclically bridged alcohol complex for the 3,5-dimethyl-2-(2′-pyridyl)pyrrole species with a nearly coplanar ring system, whereas the full DFT optimization of the 3,5-di-tert-butyl-2-(2′-pyridyl)pyrrole:methanol complex shows a break in the planarity of the ring system.