Ultracold atom technologies have transformed our ability to perform precise spectroscopy and apply it to time and frequency metrology. Many of the highest-performing atomic clocks are based on laser-cooled atoms trapped in optical interference patterns. These clocks can be applied to fundamental questions, for example to improve our understanding of gravity and general relativity. I will discuss using optically trapped molecules, rather than atoms, as a reference for clocks. Molecules have more internal quantum states and therefore are relatively challenging to control. On the other hand, their vibrational modes offer a large number of prospective clock transitions, and can help us probe alternative aspects of new physical interactions. I will also discuss the current precision limit of molecular metrology and possible paths forward.