[seminar] Predavanje dr. Gorana Zgrablica na IRBu

[hbuljan at phy.hr]

U petak 14. 5.  u 12:30 u predavaonici  I krila IRBa

     dr.sc Goran Zgrablic
     Synchrotron Trieste

odrzat ce predavanje:

     "Solvent and excitation wavelength dependence of the
      all-trans retinal Schiff base cation photoreactivity"


We present broad-band femtosecond fluorescence spectra of the protonated
Schiff base of all-trans retinal (PSBR) in various protic and aprotic
solvents [1-3], and for two excitation wavelengths when none (570 nm) or
>5000 cm-1 (400 nm) of the excess-energy is delivered in the excited-state
[3]. Possibility to investigate how different photoreactivities affect
excited-state dynamics opened up, since photoisomerisation yield in
acetonitrile increases by 50% in respect to other solvents [4]. The latter
fact, combined with detailed spectral decomposition of the time-resolved
fluorescence spectra, allowed us to assign three spectral components and
their relaxation times to either reactive or non-reactive channels. These
components clearly demonstrate the heterogeneity of the S1 state in the
sense that emission stems from several shallow potential surface minima
whose relative population ultimately determines photoreactivity of the
chromophore-solvent system. In acetonitrile, the number of fluorescence
decay channels is smaller, and the quenching of the hot fluorescence seems
more efficient.Interestingly, relative population of these minima on the
S1 in case of PSBR in acetonitrile excited at 400 nm is very similar to
the one found in PSBR in dichloromethane excited at 570 nm, suggesting
enhancement of the photoreactivity in the latter case.

Indeed, we confirmed by recent experiment [5] a 50% increase in the
photoisomerisation yield for PSBR in methanol when excited at 540 nm
instead at 400 nm. The results of our experiments hint that in order to
make PSBR photoreaction as efficient as possible, excess-energy needs to
be evacuated from the excited-state in fast (<30 fs) and efficient manner
so that extensive exploration and reaching of the non-reactive paths on
the S1 surface is avoided. Our work in progress where pump-dump-probe
technique is used to measure the PSBR photoisomerisation time constant in
various solvents will also be presented.

[1] Zgrablic, G.; Votchovsky, K.; Kindermann, M.; Haacke, S.;
Chergui, M. *Biophysical
Journal***, *88*, 2779, (2005)

[2] Zgrablic, G.; Haacke, S.; Chergui, M. *Chem. Phys.*, *338*, 168, (2007)

[3] Zgrablic, G.; Haacke, S.; Chergui, M. *J. Phys. Chem. B,* *113*,
4384-4393, (2009)

[4] Koyama, Y.; Kubo, K.; Komori, M.; Yasuda, H.; Mukai, Y. *Photochemistry
and Photobiology*, *54*, 433, (1991)

[5]     G. Zgrablic, M. Ricci, M. Novello, F. Parmigiani, *Photochem.  and
Photobio.*, *86(3)*, (2010)




--------------------------- Originalna poruka ----------------------------
Naslov: Predavanje dr. Gorana Zgrablica na IRBu
Šalje:  "Nadja Doslic" <nadja.doslic at irb.hr>
Datum:  Sri, svibanj 12, 2010 11:42 am
Prima:  hbuljan at phy.hr
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 Srdacni pozdravi,
 Nadja Doslic

-- 
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 Dr. Nadja Doslic                    E-mail: nadja.doslic at irb.hr
 Rudjer Boskovic Institute           Phone : (+385) 1 / 4561-038
 Department of Physical Chemistry    Fax   : (+385) 1 / 468-0245
 Bijenicka 54
 10002 Zagreb, Croatia
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