Reversing the arrow of time: Materials that come back to life.

The arrow of time manifests itself in a broad range of phenomena. It may be an essential ingredient that provides the underlying structure to space-time, directs a sugar cube to dissolve in a cup of coffee, and allows us to remember the past but not the future. While the microscopic processes involved are reversible, what we experience in the macroscopic world is not: a sugar cube is never observed to spontaneously emerge from a hot beverage.

Photo-induced degradation, a process that causes paper to yellow, vibrant colors in fabrics to fade, and optical devices to degrade over time is generally not reversible. We have discovered that certain molecules, when embedded in a polymer matrix, recover from photodegradation, reversing the arrow of time. We argue that the degradation process is reversed if phase space is altered in a way that limits the degradation pathways, increasing the likelihood of time-reversal. I will discuss decay and recovery of two distinct dyes that are characterized using amplified spontaneous emissions, two-photon fluorescence and linear absorption spectroscopy. Based on the data, we propose a model of the underlying mechanisms that explain how molecules come back to life, and discuss how this phenomenon can be applied to making more robust materials for useful devices.