2',7'-Difluorofluorescein

2',7'-Difluorofluorescein (Oregon green 488) is a fluorescein derivative and a pH-sensitive fluorescent probe (pK_a ~4.7). Upon excitation at 488 nm, 2',7'-Difluorofluorescein exhibits pH-sensitive fluorescence intensity through the formation of dianions, while its pH sensitivity decreases under excitation at 450 nm, allowing its use in ratiometric pH analysis. 2',7'-Difluorofluorescein can be used for the quantitative analysis of pH values in the range of 2-7 in submicron aerosol particles. 2',7'-Difluorofluorescein undergoes buffer-mediated and buffer-free excited-state proton transfer between different protonated forms, and its cationic form undergoes rapid excited-state deprotonation. 2',7'-Difluorofluorescein is resistant to photodegradation, maintains stable absorption and fluorescence properties within the physiological pH range, and serves as a fluorescent protein label, a component of Ca²⁺ indicators, a fluorescent imaging agent, and an anisotropy probe^[1][2][3]. In Vitro:2',7'-Difluorofluorescein enables ratiometric pH measurement of bulk aqueous solutions via AFC, with a pH-responsive fluorescence intensity ratio (I₄₈₈/I₄₅₀)ₙₒᵣₘ, a pK_a of ~4.7, and no significant ionic strength dependence^[1].
2',7'-Difluorofluorescein (10^-4 mass fraction; 5 s shutter interval) enables ratiometric pH measurement of sub-micrometer atmospheric aerosol particles via AFC, covering an acidic pH range of 2.38-5.35 with reasonable agreement to indicator paper measurements for most particle types^[1].
2',7'-Difluorofluorescein (5.0 μM) in aqueous solution exhibits pH-dependent steady-state fluorescence, with the cation acting as a super-photoacid and an excited-state neutral/monoanion pK_a of 2.67^[2].
2',7'-Difluorofluorescein (2.5 μM; 5 μM-1.5 M buffer concentrations) in aqueous solution with HOAc/OAc^- buffer promotes excited-state proton transfer between the monoanion and dianion forms, with an apparent excited-state pKa of 4.42^[2].