CMDITR Review of Undergraduate Research - Pluto - University of ...

Objective
The goal of the research was twofold: to
synthesize different NLO materials
(chromophores), and to make a preliminary test
of these and other chromophores (supplied by
Sei-Hum Jang) to determine chromophores or
their structure characteristics which are suitable
for the photo-crosslinking processes. As only
one finished chromophore was synthesized, this
paper will deal primarily with UV testing of
chromophores.
Research Methods
Synthesis
For the synthesis of chromophore GIM2 – a
simple chromophore – tricyanofuran (TCF)
acceptor (previously synthesized) was attached
to diethylamine benzaldehyde in a Knovenagel
condensation (Figure 1).
The Chromophores
Compounds chosen for testing were four
chromophores synthesized by Dei-Hum Jang of
the Jen group, chromophore GIM2, and EA-FTC
(Figure 2). Jang’s chromophores, abbreviated
SHJ1-SHJ4 each contained a nitrogen ring
acceptor, which was theorized to be more stable
than the traditional TCF acceptor on GIM2 and
EX-FTC. SHJ1’s π-bridge used a thiophene ring,
SHJ2-SHJ4 and GIM2 used a phenyl. SHJ2 was
eventually removed from the study because it
had not yet been fully characterized.
Solution Preparation
To make the initial doped polymer solutions,
glass vials were wrapped tightly with black
electrical tape to make them light proof. Then, in
a darkened room, 45 ± 10mg of various
chromophores with and without ethylene
linkages were combined with one, two, or no
molar equivalents of hydroxychalcone and the
polymer APC (Amorphous poly-carbonate: Poly
[Bisphenol A carbonate-co-4,4’-(3,3,5-trimethyl
cyclohexl-idene) diphenol carbonate]) in the
weight proportions 15% chromophore to 85%
APC. The solvent cyclopentanone was added in
the weight proportions 88% solvent to 12% total
solids (typically 2-3ml cyclopentanone.)
The vial was then capped, sealed with
Parafilm ® , wrapped in aluminum foil for
additional light protection, and placed on a vial
spinner and allowed to dissolve overnight
(though SHJ4 required at least a week and extra
cyclopentanone to dissolve enough.)
Spin-coating Plates
After the polymer-chromophore solution
was well dissolved, it was filtered through a
0.2µm syringe-filter and allowed to fall dropwise
onto a glass microscope plate spinning at 3000-
3500rpm to make a thin, even film on the plate.
Care was taken to avoid contact with bright light.
The plates were then placed in an unheated
vacuum oven overnight or longer to remove the
cyclopentanone residue.
Testing Plates
The removable plastic base of the UV-vis
spectrophotometer was unscrewed, and a spincoated
chromophore plate was taped to the
surface. I took an initial scan of the spectrum
from 205-1000nm, then placed the base with
plate in a high-intensity UV light box (emits
203-350nm wavelength light) for 1-, 2-, 4-, or
10-minutes, then recorded the temperature of the
inside of the box and took another scan of the
spectrum. UV exposure was continued for a
combined time total of between 20 and 50
minutes. The absorbances at the λmax of the
chromophore and of the chalcone were recorded
and graphed on Excel. A regression line was
fitted to each set of data points. Then, since
44 CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004