DNA-Enforced Conformational Restriction of an Atropisomer

We report the conformational restriction of a freely
rotating biaryl
derivative resulting in strong exciton coupled circular dichroism
between the two nondegenerate fragments of the dyad NP only in the
presence of DNA. The napthalenimide–perylenimide dyad NP, an
extended 1,1′-binaphthalene derivative, has a rotational barrier
of 100 kJ/mol, leading to fast racemization. While end-stacking with
a DNA hairpin, NP exhibits a significantly high rotational barrier,
an additional 91 kJ/mol, resulting in atroposelective preference.
Such reversible conformational constraints using biotemplates show
huge potential toward conformational analysis, dynamic kinetic resolution,
and asymmetric synthesis. The present work focuses on conformational
analysis of a freely rotating biaryl derivative using a combination
of techniques such as temperature-dependent UV–vis, circular
dichroism, steady-state and time-resolved fluorescence spectroscopy,
and molecular dynamics simulation.