Fluorescence quenching of coumarin 153 by hydroxyl-functionalized room temperature ionic liquids

• The photophysics of C151 and C153 in non-hydroxyl and hydroxyl functionalized ILs were investigated.
• [HOEmim][BF4] can quench the fluorescence of C153 while [Emim][BF4] does not.
• The slowdown of the anisotropic rotation of C153 in [HOEmim][BF4] is observed.
• There is a specific hydrogen bonding interaction between C153 and [HOEmim][BF4].

Steady-state absorption and fluorescence as well as time-resolved fluorescence of coumarin 151 (C151) and coumarin 153 (C153) were measured in hydroxyl-functionalized ionic liquids ([HOEmim][BF4] and [HOEmim][N(CN)2]) and in nonhydroxyl-functionalized ionic liquids ([Emim][BF4] and [Emim][N(CN)2]). Both the steady-state fluorescence and time-resolved fluorescence observations reveal that hydroxyl-functionalized ionic liquid quenches the fluorescence of C153 while the nonhydroxyl-functionalized ionic liquid does not. We also measured the time-resolved fluorescence anisotropy of C151 and C153 in both [HOEmim][BF4] and [Emim][BF4]. It is found that the ratio of the rotational relaxation lifetime of C153 in [HOEmim][BF4] with respect to that in [Emim][BF4] is about 15% larger than that of C151 in [HOEmim][BF4] with respect to that in [Emim][BF4], indicating extra interaction between C153 and [HOEmim][BF4] exists except the effect of the viscosity of ionic liquid.

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