title: Ultrafast and ultraslow proton transfer of pyranine in an ionic liquid microemulsion.
abstract: Effect of a room temperature ionic liquid (RTIL) and water on the ultrafast excited state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) inside a microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the surfactant, triton X-100 (TX-100) in benzene (bz) and contains the RTIL, 1-pentyl-3-methyl-imidazolium tetrafluoroborate ([pmim] [BF(4)]) as the polar phase. In the absence of water, HPTS undergoes ultrafast ESPT inside the RTIL microemulsion (RTIL/TX-100/bz) and the deprotonated form (RO(-)) exhibits three rise components of 0.3, 14, and 375 ps. It is proposed that in the RTIL microemulsion, HPTS binds to the TX-100 at the interface region and participates in ultrafast ESPT to the oxygen atoms of TX-100. On addition of water an additional slow rise of 2150 ps is observed. Similar long rise component is also observed in water/TX-100/benzene reverse micelle (in the absence of [pmim] [BF(4)]). It is suggested that the added water molecules preferentially concentrate (trapped) around the palisade layer of the RTIL microemulsion. The trapped water molecules remain far from the HPTS both in the presence and absence of ionic liquid and gives rise to the slow component (2150 ps) of ESPT. Replacement of H(2)O by D(2)O causes an increase in the time constant of the ultraslow rise to 2350 ps.
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
authors.forename: Supratik
authors.initials: S
authors.lastname: Sen Mojumdar
authors.forename: Tridib
authors.initials: T
authors.lastname: Mondal
authors.forename: Atanu Kumar
authors.initials: AK
authors.lastname: Das
authors.forename: Shantanu
authors.initials: S
authors.lastname: Dey
authors.forename: Kankan
authors.initials: K
authors.lastname: Bhattacharyya
mesh_terms: D001190:Arylsulfonates / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D044367:Phase Transition; D011522:Protons; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D001190:Arylsulfonates; D004655:Emulsions; D052578:Ionic Liquids; D011522:Protons; D014867:Water; C005047:pyranine