We report the design strategy and the synthesis of a structurally locked GFP core chromophore (Z)-4-(5-hydroxy-2,3-dihydro-1H-inden-1-ylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one(p-LHBDI  ), its ortho-derivative (Z)-4-(7-hydroxy-2,3-dihydro-1H-inden-1-ylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one(o-LHBDI  ), and (Z)-4-(2,4-dihydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (H2BDI  ) possessing both para- and ortho- hydroxyl groups in order to prove a concept that by inhibiting an inherent rotational motion of the GFP chromophores via the cyclization of the C(4)-C(5) portion, the twist along C(3)-C(4) can be restricted. o-LHBDI  possesses adoubly locked configuration, i.e., the seven-membered ring hydrogen bond and five-membered ring cyclization, from which the excited-state intramolecular proton transfer takes place, rendering a high tautomer emission quantum yield (18 % in toluene) and generating an amplified spontaneous emission. p-LHBDI  also exhibits an observable green anion emission at 500 nm with a quantum yield of 0.05 %, which is in sharp contrast to the lack of emission for the unlocked counterpart p-HBDI  anion. Partially restricting the C(3)-C(4)-C(5) via intramolecular hydrogen bonding formation, as in the case of H2BDI  , further increases the anion emission yield to 0.15 %. The leaping increase of the emission quantum yield for ortho-, para-HBDI  and H2BDI  proves that the twisting motions along C(3)-C(4)-C(5) account for the radiationless deactivation. The results demonstrate the potential of GFP core relevant chromophores in optoelectronic applications in addition to their ubiquitous exploitation in bio-imaging and bio-sensing.

Locked<i> ortho-</i> and <i>para-</i> core chromophores of green fluorescent protein: Leaping emission intensity via structural constraint

248th National Meeting (2014)

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Locked ortho- and para- core chromophores of green fluorescent protein: Leaping emission intensity via structural constraint