Ultrafast and Ultraslow Proton Transfer of Pyranine in an Ionic
Liquid Microemulsion
Supratik Sen Mojumdar, Tridib Mondal, Atanu Kumar Das, Shantanu Dey and
Kankan Bhattacharyya*
Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur,
Kolkata 700 032, India
To analyze the observed decay characteristics of HPTS, we now use a simple kinetic model as
follows
kdiss
kPT
-*….
(ROH)* + H2O
(RO
RO-* + H3O+
+
H3O )
kp[H+]w
krec
kRO-
kRO-
kROH
RO-
RO-
ROH
+
In this case, the excited state proton transfer (ESPT) process in a photoacid (ROH *) involves
three steps: initial proton transfer (kPT=1/τPT), recombination (reverse or back proton transfer) of
the geminate ion pair (krec=1/τrec) and dissociation of the geminate ion pair into solvent separated
ion pair (kdiss=1/τdiss). The differential equations corresponding to the above scheme are
= (
)[
]+
[
=
=
[
]–
[
]
Solving these differential equations, we obtain,
]
(i)
+
(ii)
(iii)
=
+
=
+
+
(iv)
(v)
where τ1 = τ4 and τ2 = τ5
According to the scheme discussed above, the decay of both the protonated form (430 nm) and
deprotonated form (540 nm) should be a sum of three exponentials.