Dr. Susovan Bhowmik discusses molecular machines, which are molecular assemblies that can be set in motion by external stimuli like pH, redox reactions, or light. In 1991, Stoddart designed a molecular shuttle that acts as a molecular machine, with a molecular bead able to shuttle between two docking stations on a molecular thread, each addressed by a different external stimulus. Examples described include a pH-triggered molecular shuttle where a paraquat ring moves between a tetrathiafulvalene unit and a dioxynaphthyl unit depending on pH, and a redox-triggered molecular shuttle where the paraquat ring moves between units when one is oxidized or reduced through application of a current.

1. Molecular Machine
Dr. Susovan Bhowmik
Bankura Sammilani College
Any Molecular assembly set in motion by external
stimuli (PH, Redox, Light) is a molecular machine

3. +e
-e
Sq. PlanarTetrahedral
Molecular Switch

4. In 1991 Stoddart[14] devices a molecular shuttle based on a rotaxane on which a molecular bead is able to shuttle
between two docking stations situated on a molecular thread. Stoddart predicts that when the stations are dissimilar
with each of the stations addressed by a different external stimulus the shuttle becomes a molecular machine.
PH Triggered Molecular Shuttle

5. PH Triggered Molecular Shuttle

6. In the ground state of the switch, the paraquat ring (Blue) is located around a tetrathiafulvalene unit (green) but it
moves to the dioxynaphthyl unit (red) when the fulvalene unit is oxidized by application of a current. When the
fulvalene is reduced back a metastable high conductance '1' state is formed which relaxes back to the ground state with
a chemical half-life of around one hour.
Redox Triggered
Molecular Shuttle

7. Molecular Elevator
0.7 nm