Vibrationally Resolved Photoelectron Spectroscopy of the Model GFP Chromophore Anion Revealing the Photoexcited S1 State Being Both Vertically and Adiabatically Bound against the Photodetached D0 Continuum.
The first excited state of the model green fluorescence protein (GFP) chromophore anion (S1) and its energy level against the electron-detached neutral radical D0 state are crucial in determining the photophysics and the photoinduced dynamics of GFP. Extensive experimental and theoretical studies, particularly several very recent gas-phase investigations, concluded that S1 is a bound state in the Franck-Condon vertical region with respect to D0. However, what remains unknown and challenging is if S1 is bound adiabatically, primarily due to lack of accurate experimental measurements as well as due to the close proximity in energy for these two states that even sophisticated high-level ab initio calculations cannot reliably predict. Here, we report a negative ion photoelectron spectroscopy study on the model GFP chromophore anion, the deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone anion (HBDI(-)) taken under low-temperature conditions with improved energy resolution. Despite the considerable size and low symmetry of the molecule, resolved vibrational structures were obtained with the 0-0 transition being the most intense peak. The adiabatic (ADE) and vertical detachment (VDE) energies therefore are determined both to be 2.73 ± 0.01 eV, indicating that the detached D0 state is 0.16 eV higher in energy than the photon excited S1 state. The accurate ADE and VDE values and the well-resolved photoelectron spectra reported here provide much needed robust benchmarks for future theoretical investigations.
†Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States.
S H M
SH
Deng
†Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States.
Xiang-Yu
XY
Kong
GuanXin
G
Zhang
†Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States.|∥State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.|⊥State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
Yan
Y
Yang
Wei-Jun
WJ
Zheng
∥State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Zhen-Rong
ZR
Sun
De-Qing
DQ
Zhang
†Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States.
Xue-Bin
XB
Wang
bright excited state; green fluorescence protein (GFP); photodetached continuum; photoelectron spectroscopy