Photoelectron spectra were recorded using our anion photoelectron imaging apparatus.32–39 Briefly, deprotonated molecular motor anions were generated by electrospray ionisation of solutions of 1a (R = COOH) in methanol with a couple of drops of ammonia added. The anions, 1a (R = COO–), were mass selected by a quadrupole and passed into a collision cell, which also acted as a hexapole ion trap to generate packets of anions at a frequency of 20 Hz to match the repetition rate of the laser system. The ions were then transported via a potential switch to the interaction region of collinear velocity map imaging optics, where they interacted with nanosecond laser pulses with wavelengths in the range 320–230 nm. Photoelectrons generated in the interaction region were accelerated towards a position sensitive detector consisting of a stack of multichannel plates, a phosphor screen and a CCD camera. Laser-only images were subtracted from images recorded following the interaction of laser light with the anions, to eliminate background counts arising from scattered light and ionisation of residual gas. The photoelectron images were inverted using the pBASEX method40 and the energy scale was calibrated by recording the photoelectron spectrum of I–. The energy resolution is around 5% and the error in electron kinetic energy is ±0.05 eV.