David Alan Leigh (born 1963)^[1] FRS FRSE FRSC is a British chemist, Royal Society Research Professor^[2] and, since 2014, the Sir Samuel Hall Chair of Chemistry in the Department of Chemistry at the University of Manchester. He was previously the Forbes Chair of Organic Chemistry at the University of Edinburgh (2001–2012) and Professor of Synthetic Chemistry at the University of Warwick (1998–2001).^[3][4]

Leigh was educated at Codsall Community High School and the University of Sheffield.^[1]

He is noted for the invention of fundamental methods to control molecular-level dynamics and entanglement, including strategies to construct rotaxanes, catenanes and molecular knots and some of the earliest synthetic molecular motors, molecular robots and functional nanomachines.

Using mechanically-interlocked molecular architectures he prepared a novel molecular information ratchet^[5] that employs a mechanism reminiscent of Maxwell's demon (although it requires an energy input and so does not challenge the second law of thermodynamics).^[6] He has developed a rotaxane based photoactive molecular switch with the capability of changing the hydrophobicity of a surface and thus causing small droplets of liquid to move up hill, against the force of gravity.^[7] In 2009 he reported the first small-molecule walker-track system in which a 'walker' can be transported directionally along a short molecular track in a manner reminiscent of the way that biological motor proteins 'walk' along biopolymers in the cell.^[8] In 2011 his research group described the smallest molecular knot prepared to date (a 76-atom-loop trefoil knot – three crossing points^[9]) and also a 160-atom-loop pentafoil knot (five crossing points).^[10] The Leigh group have also reported the synthesis of an 8₁₉ knot, the most complex molecular knot made to date,^[11] and a molecular endless knot^[12] (the smallest Chinese knot). In 2013 the Leigh group reported^[13] a small-molecule machine capable of detaching and assembling a series of amino acid building blocks from a track into a peptide of specific sequence, a very primitive version of the task performed by the ribosome. They also invented the first autonomous chemically-fuelled synthetic molecular motor^[14] and demonstrated a small-molecule 'robotic arm' able to transport molecular fragments between sites 2 nm apart on a molecular platform, marking the start of so-called 'small-molecule robotics'.^[15] In 2017 the Leigh group reported the first molecular robot that can be programmed to build different molecules.^[16] The molecular robot could be programmed to construct any one of four different stereoisomers of a molecular product, a significant step towards a 'molecular assembler'. The achievement was hailed as 'science fiction becomes fact'.^[17] In 2020 the Leigh group described the 2D weaving of polymer chains,^[18] resulting in a molecularly-woven fabric with a thread count of 40-60 million (the finest Egyptian linen has a thread count of ~1500).

In September 2016 Leigh was suggested as one of three candidates for the potential award of a Nobel Prize for synthetic molecular machines.^[19] However, on 5 October 2016 the Nobel Prize in Chemistry was awarded to J. Fraser Stoddart, Ben Feringa and Jean-Pierre Sauvage for the design and synthesis of molecular machines.^[20]

Leigh’s 8₁₉ molecular knot features in the 2019 Guinness Book of World Records.^[21] In 2018 he commissioned ‘Nanobot’,^[22] a parody by acapellascience of ‘Havana’ by Camila Cabello, describing the science behind nanorobotics. The ‘Professor David Leigh Prize for Chemistry’ at Codsall Community High School encourages girls and disadvantaged children to study science at university.^[23] Leigh is a Director and Governor of Withington Girls' School.

Leigh is a former national champion contract bridge player^[24] and an accomplished magician (ex-Edinburgh Magic Circle and the Manchester Circle of Magicians), known for blending magic and science in his public lectures.