Photoconversion of Spiropyran to Merocyanine in a Monolayer Observed using Nanosecond Pump-Probe Brewster Angle Reflectometry

A new apparatus for nanosecond-time-resolved Brewster angle reflectometry is described that can be used to measure transient angle-resolved reflectivity changes in thin films and monolayers in a single pulsed laser shot. The system was used to observe nanosecond time-resolved photodynamics in a spiropyran monolayer at the air-water interface. After UV excitation the spiropyran converted to its merocyanine form in two stages. One within a timescale close to the instrument time resolution of a few tens of nanoseconds whereas the second stage occurred over a few hundred nanoseconds.