In summary, to our knowledge
we have performed the first measurements of the excited state dynamics
of Rh-123, NADH, and FMN in aqueous solution by picosecond transient spectroscopy.
According to our investigations, rapid formation of transient species occurs
immediately after excitation of the biologically active pigments NADH,
FMN in aqueous solution. The
excited state lifetime of
the fluorescence marker Rh-123 in the aqueous solution is about 3.7 ns.
FMN exhibits biexponential transient absorption relaxation kinetics with
relaxation lifetimes t1
around 170 ps and t2
around 4.7 ns. The short relaxation lifetime of transient absorption might
be related to intermediate states appearing during formation of the long-lived
photoproduct. Further experiments are needed to characterize this photoproduct
and its intermediate states. For more precise measurements of energy relaxation
in aqueous solution of NADH, photostability of NADH has either to be studied
in detail, or experimental conditions have to be established at which NADH
is sufficiently stable.
We wish to express our gratitude
to Dr V.Vaicaitis for his assistance in making preliminary experiments
on picosecond laser spectroscopy. Financial support by the Lithuanian State
Science and Studies Foundation is gratefully acknowledged.