Photoinduced electron transfer reactions of ruthenium(II)-complexes
containing amino acid with quinones
Eswaran Rajkumara,b*, Kalayar Swarnalathaa,c, Paulpandian Muthu Mareeswarana,d,
Seenivasan Rajagopala*
Supporting Information
Materials and Methods
The ligands and ruthenium(II)-complexes were synthesized by the reported
procedures [20,38].
Absorption and emission spectroscopic measurements
Sample solutions of the Ru(II) complexes and the quenchers have been freshly
prepared for each measurement. The absorption spectroscopic measurements were carried
out using a SPECORD S100 diode-array spectrophotometer and the emission by JASCO
FP-6300 spectrofluorimeter. All the sample solutions used for emission measurements
were deaerated for about 20 min by dry nitrogen gas purging and keeping the solutions in
cold water to ensure that there is no change in volume of the solution.
Electrochemical measurements
Electrochemical measurements were carried out using cyclic voltammetric
technique using EG & G Princeton Applied Research Potentiostat / Galvanostate Model
273A. Samples of 1mM solutions of the Ru(II) complexes were prepared in acetonitrile
media. The setup consists of three electrode system in which the working electrode is
glassy carbon electrode, standard calomel reference electrode and platinum counter
electrode. Tetra-n-butyl ammonium perchlorate (0.1M) was used as the supporting
electrolyte. Cyclic voltammograms were recorded after purging the solution with dry
nitrogen gas for 30 min. The redox potentials of the ground state couples and E0-0, the
energy corresponding to zero-zero transition give the excited state redox potentials of
Ru(II) complexes.
Luminescence lifetime measurements
Fluorescence decays were recorded using time correlated single photon counting
(TCSPC) method using the following set up. A diode pumped millena CW laser (Spectra
Physics) 532 nm was used to pump Ti:Sapphire rod in Tsunami picosecond mode locked
laser system (Spectra Physics). The 750 nm (80 MHz) line was taken from the
Ti:Sapphire laser and passed through a pulse picker (Spectra Physics, 3980 2s) to
generate 4MHz pulses. The second harmonic output (375 nm) was generated by a flexible
harmonic generator (Spectra Physics, GWU 23 ps). The vertically polarised 375 nm laser
was used to excite the sample. The fluorescence emission at the magic angle (54.7º) was
dispersed in a monochromator (f/3 aperture), counted by a MCP PMT (Hamamatsu R
3809) and processed through CFD, time-to-amplitude converter (TAC) and multichannel
analyzer (MCA). The instrument response function for this system is ≈ 52 ps and the
fluorescence decay was analyzed by using the software provided by IBH (DAS-6) and
PTI global analysis software.
Transient absorption measurement
Transient absorption measurements were made with laser flash photolysis
technique using an Applied Photophysics SP-Quanta Ray GCR-2(10) Nd:YAG laser as
the excitation source. The time dependence of the luminescence decay is observed using
a Czerny-Turner monochromator with a stepper motor control and a Hamamatsu R-928
photomultiplier tube. The production of the excited state on exposure to 355 nm was
measured by monitoring (pulsed Xenon lamp of 250W) the absorbance change. The
change in the absorbance of the sample on laser irradiation was used to calculate the rate
constant as well as to record the time-resolved absorption transient spectrum. The change
in the absorbance on flash photolysis was calculated using the expression
log (I0/(I0 – I
II–It)
Where  is the change in the absorbance at time t, I0, I and It are the voltage after flash,
the pre-trigger voltage and the voltage at particular time respectively. A plot of ln(∆At –
∆A∞) vs time gives a straight line. The slope of the straight line gave the rate constant for
the decay and the reciprocal of rate constant gave the lifetime of the triplet. The timeresolved transient absorption spectrum was recorded by plotting the change in absorbance
at a particular time vs wavelength.
Figure Captions
Figure S1: Absorption spectrum of II with incremental addition of quinone (a)
methylbenzoquinone(2×10-5 - 2×10-4 M) (b) napthaquinone(5×10-5 - 5×10-4M).
Figure S2: Absorption spectrum of III with incremental addition of quinone (a)
benzoquinone (2×10-5 - 5×10-4 M) (b) chloroanil (2×10-5 - 2×10-4 M)
Figure S3: Transient absorption spectrum recorded after excitation of V in
acetonitrile solution at 298 K at different time intervals.
Figure S4: The decay of the 2,6-dichlorobenzoquinone anion radical at 410 nm at
different time scale.
(b)
(a)
Figure S1: Absorption spectrum of II with incremental addition of quinone (a)
methylbenzoquinone(2×10-5 - 2×10-4 M) (b) napthaquinone(5×10-5 - 5×10-4M)
(a)
(b)
Figure S2: Absorption spectrum of III with incremental addition of quinone (a)
benzoquinone (2×10-5 - 5×10-4 M) (b) chloroanil (2×10-5 - 2×10-4 M)
Figure S3: Transient absorption spectrum recorded after excitation of V in
acetonitrile solution at 298 K at different time intervals.
Figure S4: The decay of the 2,6-dichlorobenzoquinone anion radical at 410 nm at
different time scale.