Decoupling Electronic versus Nuclear Photoresponse of Isolated Green Fluorescent Protein Chromophores Using Short Laser Pulses

The photophysics of a deprotonated model chromophore for the green fluorescent protein is studied by femtosecond laser pulses in an electrostatic ion-storage ring. The laser-pulse duration is much shorter than the time for internal conversion, and, hence, contributions from sequential multiphoton absorption, typically encountered with ns-laser pulses, are avoided. Following single-photon excitation, the action-absorption maximum is shown to be shifted within the S-0 to S-1 band from its origin at about 490 to 450 nm, which is explained by the different photophysics involved in the detected action.