Quick on the draw chemists have developed molecules that can recreate simple pictures in outline. The work builds on previous logical units that can detect the edges in an image and could lead the way to novel approaches to micro- and nano-lithography for constructing molecular machines and circuits.

Edge detection is an important process in computerized pattern recognition as well as in digital image manipulation where it is used to improve and artificially "sharpen" photos and other graphic content. Earlier this year a team led by Prasanna "AP" de Silva at Queen's University Belfast, Northern Ireland, UK, and colleagues published the results of a study in which they used molecular logic units to detect the edges in an image. [de Silva et al, J Am Chem Soc, 2015, 137 (11), pp 3763–3766; DOI: 10.1021/jacs.5b00665]The same team has now taken this concept a step further to demonstrate how a molecular system can not only detect edges but visualize those edges, essentially drawing an image in outline. De Silva and his colleagues demonstrated proof of principle by persuading their logical molecules to draw a picture of a bird and of a shamrock in outline from a template.

"Our JACS paper on edge detection involved molecules emulating something we and all animals do subconsciously. Now, we demonstrate molecular emulation of something we humans do consciously and call a valuable part of our shared culture: drawing," de Silva told Materials Today. He points out that the simplest drawing technique, i.e. outline drawing, is accomplished in the latest paper. The team has used a photo acid generator (triphenylsulfonium chloride, which was first developed by IBM for etching 3D features into wafers of silicon to make the microscopic components on their chips), a fluorescent pH sensor (such as perylenetetracarboxylic-3,4,9,10-bis[2'-(morpholino)ethyl]imide) and a sodium carbonate pH buffer.

By shining ultraviolet light through a mask (bird or shamrock) on to a piece of filter paper soaked in the chemical agents and partially dried, the team can watch as exposed areas become acidic. This activates the fluorescence of the sensor molecule to generate a "positive", as opposed to a negative of the mask. The hydrogen ions then diffuse slowly into the non-irradiated regions, which activates the fluorescent sensors in the adjacent border. Under prolonged irradiation, a photoproduct accumulates that quenches the sensor fluorescence so that the irradiated regions lose their glow, revert to the dark state, and leave behind, the outline, the edge, only of the mask. See image, courtesy of Royal Society of Chemistry/de Silva et al.

"The logical molecular system dutifully outputs an outline drawing, who would have thought that logical molecules could draw?" de Silva told us. He and his colleagues have now developed a semi-quantitative model of the process. [de Silva et al, Chem Sci, 2015, in press; DOI: 10.1039/c5sc01537e]

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".