Absorption of the green fluorescent protein chromophore anion in the gas phase studied by a combination of FTICR mass spectrometry with laser-induced photodissociation spectroscopy

Abstract

The optical absorption of the green fluorescent protein chromophore anion (HBDI −) in the gas phase has been addressed by a number of experimental and theoretical studies; however, there is no consensus on its spectral characteristics yet. In this report, the intrinsic absorption of HBDI − was probed by photo-induced dissociation (“action”) spectroscopy using discrete lines of a continuous-wave (CW) laser source. The observed spectral profile of dissociation efficiency revealed a pronounced dependence on the laser irradiance. Dissociation at high irradiance is governed by multiple-photon absorption processes whose efficiency peaks between 476 and 488 nm. At very low irradiance (<0.4 mW cm −2) dissociation of gas-phase HBDI − is mostly promoted by single-photon transitions and suggests an intrinsic absorption maximum of gas-phase HBDI − <476 nm, blue-shifted compared to earlier results obtained with pulsed lasers.