Rudolph Marcus, a theoretical chemist who spent a century alive and much of it illuminating the hidden logic of electrons in motion, died Thursday in Pasadena at 102. Working not at the laboratory bench but in the realm of ideas, he constructed a framework that revealed the molecular machinery behind photosynthesis, cellular respiration, and even the glow of fireflies — processes so fundamental they underpin life itself. His 1992 Nobel Prize in Chemistry honored a theory that did not merely explain one phenomenon but opened a way of seeing that chemists continue to use across the full breadth