4th EucheMs chemistry congress

thursday, 30-Aug 2012
s828
chem. Listy 106, s587–s1425 (2012)
Physical, theoretical and Computational Chemistry
Ultra fast Processes – i
o - 5 0 6
StruCturAL dynAMiCS of CovALent
PeryLene-BASed SySteMS ProBed with
feMtoSeCond StiMuLAted rAMAn
SPeCtroSCoPy
K. Brown 1 , B. veLdKAMP 1 , d. Co 1 ,
M. wASieLewSKi 1
1 Northwestern University, Chemistry, Evanston, USA
Understanding the charge transfer (CT) dynamics on the
femtosecond to picosecond timescale provides crucial information
to the development of bio-inspired photocatalytic systems for
solar fuels and solar energy. For several donor-acceptor systems,
the CT state remains a convolution of locally excited states (ES)
or radical ion pairs, which prove difficult to understand using time
resolved spectroscopy. However, spectroscopic techniques such
as transient absorption give little useful information relaying
structural information in the excited state and CT processes that
occur on the fs to ps time scale. In order to obtain simultaneous
high temporal and spectral resolution, it is necessary to have a
structural probe with sub-picosecond time resolution. The recent
development of femtosecond stimulated Raman spectroscopy
(FSRS) enables observation of vibrational structural information
with resolution comparable to vibrational dephasing times. FSRS
also has the advantage of being insensitive to fluorescence, which
can hinder the use of structural techniques such as spontaneous
Raman spectroscopy for broadly used, solar-driven chromophores
such as perylene diimide (PDI, ε=80,000 M-1 cm-1 ).
We demonstrate the use of FSRS to elucidate ES and CT
dynamics of various perylene-based chromophores. Here we
present a study of picosecond vibrational dynamics of the CT and
ES of perylene, PDI, and perylene monoimide (PMI). Evaluation
of these chromophores reveals strong C = C core stretching
vibrations that, though consistent in the ground state, vary
significantly upon excitation to the first excited state, S1 . For
instance, a strong, dispersive feature at 1593 cm-1 is solely present
in the ES of PDI, suggesting the utilization of a new vibrational
coordinate. Analysis of the photoreduced PDI anion in a dyadic
system demonstrates significant contributions from these
additional modes. Understanding the structural motion of different
states will provide needed insight as we move to effectively design
an efficient solar fuel.
Keywords: Electron Transfer; Charge Transfer; Photophysics;
Raman spectroscopy; Time-resolved Spectroscopy;
Ultra fast Processes – ii
4 th EucheMs chemistry congress
o - 5 0 7
uLtrA-fASt LASer MAteriALS ProCeSSinG
w. KAuteK 1
1 University of Vienna, Department of Physical Chemistry,
Vienna, Austria
Femtosecond Nanoscale Processing is reviewed for a wide
variety of representative material classes, such as metals,
semiconductors, dielectrics, ceramics, polymers, and biopolymers.
The photo-electronic excitation mechanisms of these materials are
compared in terms of incubation phenomena and material-specific
electronic behaviours [1, 2] . An increase of pulse duration and pulse
repetition rate into the megahertz range yielded a rising
contribution of thermal excitation. Non-thermal and thermal
processes, which determine the extent of the heat-affected zones,
could be identified during the ablation process. Laser-induced
periodic surface structures depend on the pulse length, the laser
fluence, the number of laser pulses, the polarization, and on the
shape of temporally tailored pulses [3, 4] . New insights into such
self-assembly phenomena induced by femtosecond laser treatment
on solid materials were gained. Current work with optical-field
enhancement and confinement for an asymmetrically illuminated
nanoscopic SFM tip illuminated by fs-laser pulses suspended over
different materials is shortly reported. Since the first fundamental
femtosecond pulse laser ablation studies on human corneas [5] ,
the use of sub-picosecond laser experienced vivid attention in
surgery [6] . These processes involve non-linear optical coupling
being highly dependent on the local intensity.
references:
1. W. Kautek, in “Laser Ablation and its Applications”,
Ed. C. Phipps, Springer, Norwell, Mass. USA 2006, p. 215.
2. W. Kautek and M. Forster, Springer Series in Materials
Science 135 (2010) 189.
3. M. Forster, L. Égerházi, C. Haselberger, C. Huber and
W. Kautek, Appl. Phys. A 102 (2011) 27.
4. M. Forster, W. Kautek, N. Faure, E. Audouard, and
R. Stoian, Phys. Chem. Chem. Phys. 13 (2011) 4155.
5. W. Kautek, S. Mitterer, J. Krüger, W. Husinsky, and
G. Grabner, Appl. Phys. A58 (1994) 513.
6. G. Grabner, Spektrum Augenheilkd. 23 (2009) 187.
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc