Solvatochromic Fluorescence of a GFP Chromophore-Containing Organogelator in Solutions and Organogels.

Solvatofluorochromism, a solvation effect on the fluorescence color of an organic dye, is a property generally limited to fluid solutions. We demonstrate herein the concept of solid-state solvatofluorochromism by using an organogelator (1-SG), which consists of a solvatofluorochromic green fluorescence protein (GFP) chromophore (1) and a sugar gelator (SG). While 1-SG could be located in the liquid phase or in the fibrous solid matrix of the SG gel, our results show that the one in the solid matrix but near the liquid interface has superior fluorescence stability and quantum efficiency as well as solvatofluorochromicity than the one in the liquid phase. In addition, the phenomenon of fluorescence turn-on occurs when the gel is formed in protic solvents. These features have been applied to perform multicolor fluorescence patterning, chemical vapor sensing, data encryption and decryption, and real-time fluorescence cell imaging.

Hydrogen Bonding-Induced H-Aggregation for Fluorescence Turn-On of the GFP Chromophore: Supramolecular Structural Rigidity.

To turn on the fluorescence of the native green fluorescence protein (GFP) chromophore, 4-hydroxybenzylidene-dimethylimidazolinone (HBDI), in an artificial supramolecular system has been a challenging task, because it requires high local environmental rigidity. This work shows that the formation of H-aggregates of an HBDI-containing organogelator results in two orders of magnitude fluorescence enhancement (Φf =2.9 vs. 0.02 %), in which the inter-HBDI OH⋅⋅⋅OH H-bonds play a crucial role. The aggregation-induced fluorescence enhancement of HBDI has important implications on the origin of the high fluorescence quantum efficiency of HBDI in the GFP ß-barrel and on the supramolecular strategy for a full fluorescence recovery of HBDI. These results reveal a new approach to designing rigid chromophore aggregates for high-performance optoelectronic properties.

Fluorescence Enhancement of Unconstrained GFP Chromophore Analogues Based on the Push-Pull Substituent Effect.

Unlike the high fluorescence quantum yield of the naturally occurring green fluorescence protein (GFP, Φf ∼ 0.8), the GFP chromophore, a benzylidenedimethylimidazolinone (BDI) dye, is nearly nonfluorescent (Φf < 0.001) in common solutions at room temperature. While many efforts have been devoted into the BDI chromophore engineering for fluorescence recovery, limited success has been achieved for structurally unconstrained GFP chromophore analogues (uGFPc). Herein we report a rational design of uGFPc toward an unprecedentedly high fluorescence quantum efficiency of 0.60 in hexane. This is achieved by a combined ortho-CN and meta-dimethylamino substituent electronic effect that largely suppresses the Z → E photoisomerization (the τ torsion) reaction, which is the major nonradiative decay channel of uGFPc. The structural design relied on the assumptions that the τ torsion of the meta-amino-substituted BDI systems leads to a zwitterionic twisted intermediate state (1p*) and that destabilizing the 1p* state by an electron-withdrawing CN substituent at the ortho or para position could slow down the τ torsion. The observed CN position effect conforms to the design concept. The push-pull substitution of BDI also leads to sensitive fluorescence-quenching responses to electron donors such as trimethylamine and to H-bond donors such as methanol.