Intermolecular attractions between two parts within an arylene ethynylene molecule are of interest to our research, specifically with respect to electronic properties that can be monitored via UV-vis spectroscopy. Each system in this study was designed around a pyrazine free-rotor placed between two groups that might restrict rotation of the central benzene ring via halogen or hydrogen bonding. Compound A, an intermediate in the synthesis of B and C, exhibits interesting electronic properties when analyzed using UV-Vis spectroscopy due to conventional hydrogen bonding. This compound displays differing λmax shifts depending on solvent choice. Compound B is expected to demonstrate similar λmax shifting behavior due to halogen bonding between the electropositive region of X and the electron dense nitrogen on the pyrazine. Compound C is a very interesting case of non-conventional hydrogen bonding. This differs from conventional hydrogen bonding, defined as the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. In our molecule the hydrogen is bonded to carbon, but is still attracted to the pyrazine nitrogen due to the electron withdrawing effect of the fluorinated benzene system (C). Bathochromic shifts (red shifts) are dependent on the effective conjugation of the unsaturated system. Strong, intramolecular halogen and hydrogen bonds restrict rotation of the central pyrazine rings. Without these attractions, each linear carbon has free-rotation, which should provide less effective conjugation.

Intermolecular halogen bonding and non-conventional hydrogen bonding in arylene ethynylene oligomers

253rd National Meeting (2017)

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