This document summarizes research on understanding the temperature dependence of local domain photophysics. The objectives are to understand how the local environment (domain) interacts with probe molecules and how this gives rise to photophysical behavior. The experimental setup uses confocal fluorescence microscopy to study probes like violamine R in polymer domains like poly(vinyl alcohol) across a temperature range. Preliminary results show power law distributions and differences in memory effects between domains that can exchange probe molecules more or less quickly. Future work aims to explore different probe molecules and polymer domains to better understand these interactions.
2. Why do we care?
• Center for Materials and Devices for
Information Technology Resources
• A lot of interest lies in using
chrimophores and polymer complexes
• We are generally interested in the
electro-optic (EO) activity of these
devices
3. Why aren’t they used?
• There are a couple main points
limiting widespread application
• Chromophore robustness (irreversible
photo-decomposition)
– Fluorescent intermittency studies
4. What are the objectives of my
research?
• The main objectives are:
• Understand the relation between the local
environment (domain) and the
chromophore (probe)
• Understand the probe-domain interactions
that give rise to the population and
depopulation of the dark state
• Increase understanding of SM
photophysics, which are surprisingly
complex
5. What variables can we control?
• Probe
– Size
– Shape
– Functional groups
• Domain
– Glass transition temperature (Tg)
– Side groups
• Temperature
– How does a change in the thermal energy of the
system affect photophysics?
9. Power Law Plots
• Power law (PL) plots are indicative of distributed
kinetics
• Roll off on the plots means that it is moving to
a more single exponential distribution
10. Memory Plots
• A density of points along the diagonal indicates
memory
• Memory is related to domain exchanges
• However, due to poor statistics, SM memory plots
11. Solid Walled Pockets
• In studies performed by Orrit and
coworkers (Zondervan, 2007), they showed
that some polymers exhibit domains that
are slow to exchange with the local
environment, even above Tg.
• The evidence for a slow exchange is that
there is not a drastic jumps in the
rotational timescales of the probe
molecules
12. Support for SWPs
• PVOH is able to hydrogen bond
– Is known to h-bond with itself
– Orrit and coworkers showed SWPs for glycerol
and o-terphenyl, both which are capable of
intra-polymer bonding
• H-bonds in glycerol
• Stacking in o-terphenyl
• PMA does not hydrogen bond, or at least
not as easily
– Memory plots are very different than those of
PVOH
13. Domain stress
• The free volume of the polymers is
much smaller than that of the Van der
Waals radii of the probes
• Free volume expansion by
introduction of probe may increase
side chain interactions, such as
hydrogen bonds
• This may be a cause for SWPs
14. Limitations
• There are a few limitations with the
VR/PVOH system
• VR is not the best choice
• Single domain, comparisons between
multiple systems would be good
• KAP
• PMA
15. Problems with VR
• One of the downsides to using VR is
that it comes as a relatively low dye
content (60-65%)
• The question is what is the other
~40%?
– Is it also fluorescent, particularly at 532
nm?
• Also, the fluorescence of VR is solvent
dependent
16. Differences between domains
• PVOH
– Simple structure
– Can form hydrogen bonds between itself as well
as the probe
• KAP
– Crystal
– Domain is constant
– Oxygen impermeable
• PMA
– Longer side chain
– Has a relatively high chain mobility
17. Reduced temperature scale
• Reduced temperature scale is relative
to a polymers Tg
• By looking at T/ Tg, we are able to
directly compare chain mobilities, even
though the absolute temperatures may
be different
18. Comparing domains in the reduced
scale
• The results of VR/PMA (23˚C) compare
to the VR/PVOH (85˚C)
– T/ Tg is ~1.04
• The overall shape of the PL plots are
the same
– Both exhibit roll offs at the ends
• However, one big difference is the
density of points is much greater in
19. What do we get out of this?
• PL distributions are similar, but
memory is different
• The processes that are responsible for
the population and depopulation of
the dark state are consistent between
the two domains, but in PMA, the
domain is able to exchange much
more quickly than PVOH, resulting in a
loss of memory
20. Where do we go?
• PVOH and PMA share a complication.
– It is difficult to properly span the Tg in
both polymers.
– PMA has a relatively low Tg (~9˚C)
– PVOH has a relatively high Tg (~72˚C)
• Use a polymer that has a Tg that can
be easily covered
– Poly(isobutyl methacrylate) (PiBMA)
21. Why PiBMA?
• PiBMA has a mid-range Tg (~55˚C)
• The structure is similar to PMA
• PiBMA has been used in previous EO/
SHG studies (Dhinojwala, 1993)
• PiBMA is a fairly common polymer
22. Change the probe
• Size
• Shape
• Functional groups
• DCM is a common laser dye, which has
also been used in previous studies by
our group
23. DCM
• Dye content is 98%, as opposed to VR
which has a dye content of 60%
• Hydrogen bonds formed with DCM
may be weaker than those formed with
VR
24. Europium
• Europium (Eu) is fluorescent
• Adding ligands increases size
• Does the size of the Eu complex affect
domain exchanges?
• Will an increase in stress on the
polymer result in slower exchanges?
25. What have we done?
• First Act
– Violamine R (VR) in poly(vinyl alcohol)
(PVOH)
• Second Act
– VR in potassium acid phthalate (KAP)
• Third Act
– VR in poly(methyl acrylate) (PMA)
