Synthesized Blue Fluorescent Protein Analogue with Tunable Colors from Excited-State Intramolecular Proton Transfer through an N-H···N Hydrogen Bond.
A synthesized blue fluorescent protein (BFP) chromophore analogue 2-BFP ((4Z)-4-[(1H-imidazol-2-yl)methylene]-1-methyl-2-phenyl-1H-imidazol-5(4H)-one) displays dual fluorescent emission that arises from the same Z-isomer. The larger Stokes shift emission is a result of excited-state intramolecular proton transfer (ESIPT) mediated by an N-H···N type of hydrogen bond. Compared to other green fluorescent protein (GFP) analogues with ESIPT such as o-HBDI, 2-BFP possesses greatly enhanced quantum yields and much slower proton-transfer rates. In addition, fluorescence up-conversion experiments revealed two rising components of lifetime for the tautomer formation of 2-BFP. The results imply that the relaxation of the N* state in 2-BFP triggers the proton transfer of the molecule. The weaker photoacidity of N-H is proposed to be crucial for these photophysical and photochemical properties. Finally, the ESIPT process in 2-BFP is inhibited in protic solvents (MeOH) or by the formation of metal-chelate complexes, providing insights for further developments and applications of ESIPT molecules.
†The State Key Laboratory of Electroanalytic Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
Xinxiu
X
Fang
Yan
Y
Wang
Dan
D
Wang
†The State Key Laboratory of Electroanalytic Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
Guiyan
G
Zhao
†The State Key Laboratory of Electroanalytic Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
Wenwen
W
Zhang
Aimin
A
Ren
Haiyu
H
Wang
†The State Key Laboratory of Electroanalytic Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
Jingwei
J
Xu
Bing-Rong
BR
Gao
†The State Key Laboratory of Electroanalytic Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
Wei
W
Yang
dual fluorescent emission; excited-state intramolecular proton transfer; fluorescence quantum yield; fluorescence up-conversion; green fluorescent protein; proton-transfer rate