Acid/Base
and H<sub>2</sub>PO<sub>4</sub><sup>–</sup> Controllable High-Contrast
Optical Molecular Switches with a Novel
BODIPY Functionalized [2]Rotaxane
A novel multifunctional mechanically
interlocked switchable [2]rotaxane <b>R4</b> containing two
molecular stations and rotaxane arms terminated
with boron-dipyrromethene (BODIPY) fluorophores and its derivatives
were synthesized for the first time by CuAAC click reaction. The shuttling
motion of macrocycle between the dibenzylammonium and triazolium recognition
sites and the distance dependent photoinduced electron transfer process
of <b>R4</b> is demonstrated by utilizing external chemical
stimuli (acid/base). Interestingly, the reversible self-assembly process
of <b>R4</b> was recognized by the acid–base molecular
switch strategy. Notably, two symmetrical triazolium groups acted
as molecular stations, H<sub>2</sub>PO<sub>4</sub><sup>–</sup> receptors, and H-bonded donors. Both [2]rotaxane <b>R4</b> and thread <b>R2</b> demonstrated excellent optical responses
and high selectivity toward H<sub>2</sub>PO<sub>4</sub><sup>–</sup> ion. The specific motion and guest–host interactions of mechanically
interlocked machines (MIMs) were also further explored by quantum
mechanical calculations. The thread <b>R2</b> also demonstrated
to enable the detection of H<sub>2</sub>PO<sub>4</sub><sup>–</sup> in RAW 264.7 cells successfully