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Influence of Rotator Design on the Speed of Self-Assembled Four-Component Nanorotors: Coordinative Versus Dispersive Interactions
journal contribution
posted on 2017-05-17, 00:00 authored by Pronay Kumar Biswas, Suchismita Saha, Yerramsetti Nanaji, Anup Rana, Michael SchmittelFour-component nanorotors
are prepared by the self-assembly of stator [Cu4(4)]4+ with its four copper(I)-loaded phenanthroline
stations and various rotators carrying one, two, or three pyridine
terminals. The fourth component, 1,4-diazabicyclo[2.2.2]octane, serves
as
a connecting axle between rotator and stator. Capitalizing on the
heteroleptic pyridyl and phenanthroline metal complexes concept, the
rotator’s pyridine terminals are connected to the copper(I)-loaded
phenanthroline stations (Npy → [Cu(phen)]+) in the STOP state and disconnected in the transition state of rotation.
As the barrier of the thermally activated rotation, measured by variable-temperature 1H NMR, is mainly governed by attractive forces between stator
stations and rotator terminals, it increases along the series Ea (monopyridine rotator) < Ea (dipyridine rotator) < Ea (tripyridine rotator). However, there are even distinct differences
in rate between rotors with equal number of rotator terminals. The
change from the 5,10-dipyridyl (cis) to 5,15-dipyridyl
(trans) zinc porphyrin rotator enhances the rotational
frequency by almost 1000-fold. Density functional theory computational
results suggest that not only coordinative Npy →
[Cu(phen)]+ interactions but also dispersive attraction
influence the barrier of rotation.