Chun‐Wei ChiuLi‐Ling TsaoHsuan‐Yu LinYi‐Hung LiuMarco RaabeChing‐Wei LinYuan‐Chung ChengJye‐Shane Yang2025-03-192025-03-192025-02-23https://scholars.lib.ntu.edu.tw/handle/123456789/725856Flexible solvatochromic fluorescent dyes (SFD) typically exhibit a decrease in fluorescence quantum yield (ΦF) and a red shift in fluorescence with increasing solvent polarity. In this study, we report a new E,Z-isomerization-active green fluorescence protein chromophore (GFPc) analogue (4), which uniquely demonstrates a reversed solvent polarity effect on ΦF and a record-high ΦF of 0.43 in the red (>600 nm) region. This is achieved by ring-bridging both the exocyclic C−C bond (the ϕ-bond) and the phenyl-amino C−N bond (the ω-bond) of a known meta-amino-substituted GFPc (1), which shows typical SFD behavior in aprotic solvents but fluorescence quenching in protic solvents. Based on the reference compounds 2 (ω-bridged) and 3 (ϕ-bridged), the reversed solvent effect is attributed to enhanced one-bond-flip (OBF) E,Z-isomerization in nonpolar solvents and the inhibition of hula twist (HT) pathway, which is accelerated in polar solvents. The drastic difference in fluorescence characteristics between 1 and 4 is further underscored by the superior performance of 4 in cell imaging. This work demonstrates the versatility of the GFP chromophore, whose properties could be drastically reshaped through specific structural editing at key positions.endonor-acceptor systemsE-Z photoisomerizationfluorescence solvatochromismimaging agentsphotochemistry[SDGs]SDG3journal article10.1002/cptc.202400400