One of Uhlig’s cards, for instance, describes a moment of desire. Illustrated on the card face are two molecules: The one on the left is a diene, and on the right is an alkene. Shown just moments before their inevitable coupling via the Diels-Alder reaction, the two molecules meant for one another are separated by only a heartbeat. “I’m diene to be with you,” reads the message on the card.
Source : https://cen.acs.org/articles/94/i6/Valentines-Day-Cards-Heart-Felt.html