A theoretical study of the effects produced by N-hydroxyalkyl substitution in pyrrole oligomers

This work reports a quantum mechanical investigation of the effects produced by the N-hydroxyalkyl substitution on the molecular and electronic structure of pyrrole-containing oligomers. First, the molecular geometry, torsional potential, ionization potential and π-π* transition energy predicted for N,N′-dihydroxymethyl-2,2′-bipyrrole and N,N′-dihydroxypropyl-2,2′-bipyrrole have been compared with those obtained for 2,2′-bipyrrole and N,N′-dimethyl-2,2′-bipyrrole. After this, the properties of pyrrole and N-hydroxymethylpyrrole-containing oligomers formed by n repeating units, where n ranges from 1 to 5, have been examined. Results are explained as a combined actuation of electron donation effects induced by the hydroxyl groups, repulsive steric interactions generated by the N-substitution and attractive specific interactions associated to the hydroxyl groups.