This document summarizes research on using the enhanced electric field generated by surface plasmons on gold nanoparticles to non-resonantly excite photochromic molecules. The researchers coated gold nanospheres with a photochromic molecule called DAE1 and showed that 800nm light, which does not normally convert DAE1, was able to do so in the presence of the nanoparticles. They varied experimental conditions like nanoparticle size and structure. Images were also taken of plasmonic antennas made of nanorods that generate even stronger electric fields and could potentially induce conversion at even longer wavelengths than 800nm.

1. Non-Resonant Excitation of Photochromic Molecules in
the Plasmonic Field of Gold Nanoparticles
Ryan W. Hamelin1, Chris Otolski2, Christopher G. Elles2
1Department of Chemistry, Fitchburg State University, Fitchburg, Massachusetts, 01420
2Department of Chemistry, University of Kansas, Lawrence, Kansas, 66045
Abstract
Photochromic molecules undergo reversible photochemical reactions that convert the compound between different isomeric structures. Irradiating gold
nanoparticles creates surface plasmons that can be used for non-resonant excitation of photochromic molecules. This research shows that irradiating a
photochromic molecule with 800nm light, a wavelength that would not normally transform the molecule, can convert the molecule, due to the intense
electric field generated by the surface plasmons. The conversion was observed in samples consisting of a film of 20nm gold nanospheres, coated with a
layer of photochromic 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)hexafluoro-1-cyclopentene (DAE1) in a polymer matrix. The non-resonant conversion
of DAE1 using 800nm light was studied further by varying the conditions of the experiment. These variations include changing the size or structure of
the gold nanoparticles and the different ways of fabricating the sample.
Plasmonic Antenna
• Greater intensity of electric field than gold nanospheres, as shown in the simulations by Guillaume et. al.
• Have yet to be imaged using transmission measurements
• Have a greater possibility of inducing a non-resonant excitation of photochromic molecules
Background
Photochromic Molecules:
• Considered to be a “…promising mechanism for erasable data storage…” (Ward)
in solid form
• Can switch between isomers thousands of times without fatigue
• Different absorbance spectra depending on their structures,
which changes when irradiated
Surface Plasmons:
• Oscillating surface electrons
• Create an enhanced electric field due to light separating the charges on a metal substance
• Can be used to increase the possibility that a non-resonant excitation, the absorbance
of two photons to excite the molecule into a longer lived excited state, will occur
Non-Resonant Excitation in a Plasonic Field:
• Absorbing multiple photons, at the same time, to excite the molecule
• Caused by the enhanced electric field between gold nanoparticles
• Creates a higher probability of conversion
Acknowledgements
The Elles Group
Sasanka Ulapane and the Berrie Group for letting us use their equipment and taking images of the plasmonic antenna
National Science Foundation under Research Infrastructure Improvement Award IIA-1430439
NSF-REU program CHE-1263259
The Department of Chemistry at KU
Photoswitch Irradiated with 400 and 800nm Light
400nm light converts DAE1 but 800nm light does not, in the absence of nanoparticles. This experiment was run to see if the enhanced electric field,
created by the surface plasmons of the gold nanospheres, can cause an excitation using 800nm light and convert DAE1
References
Experimental Method
Sample Preparation:
• Create a layer of silane coupling agent on a glass substrate
• Place gold nanospheres on sample, bonding the nanospheres to glass
• Drop cast, or spin coat, a solution of photoswitch onto the sample
Sample Measurement:
• Convert the DAE1 into closed form by irradiating it with UV light until it is completely converted
• Irradiate the sample with 400nm or 800nm light and measure the conversion that occurs as DAE1
switches back to open form
Guillaume Baffoua and Romain Quidant. Chem. Soc. Rev., 2014, 43, 3898
Maria Becker, Wayne Cheng-Wei Huang,Herman Batelaan, Elisabeth J. Smythe and Federico Capasso. Ann. Phys., 2013, 525, L6-L11
Tsuboi, Yasuyuki, Ryosuke Shimizu, Tatsuya Shoji, and Noboru Kitamura. J. Am. Chem. Soc.131.35 (2009): 12623-2627.
Ward, Cassandra L., and Christopher G. Elles. J. Phys. Chem. Lett. 3.20 (2012): 2995-3000
Image of the plasmonic
antenna (Au nanorods)
and its thickness
DAE1’s Absorbance
Spectrum in Open and
Closed Form
Results of simulations
done by Guillaume et.
al. showing the
increased electric field
formed by different
nanoparticles
This is an image taken of a plasmonic antenna, an alignment of nanorods that generates an intense electric field. This graph is the first transmission
measurement taken of a plasmonic antenna and shows the different absorbance plots that can be obtained by the way the light is polarized. This antenna
should cause photochromic molecules to absorb photons at wavelengths longer than 800nm.
These results show, that in the presents of gold nanospheres, 800nm light can convert DAE1 between isomers. Nanoparticles can cause photochromic
molecules to absorb longer wavelengths causing a non-resonant excitation.
0.12
0.08
0.04
0.00
Absorbance
600500400
Wavelength (nm)
0mins
5mins
10mins
15mins
0.12
0.08
0.04
0.00
Absorbance
650600550500450400
Wavelength (nm)
0mins
5mins
10mins
20mins
30
20
10
0
x10
-3
700650600550500450
Wavelength (nm)
0mins
2mins
4mins
6mins
8mins
10mins
400nm Light Excitation of DAE1 800nm Light Excitation of DAE1
800nm Light Excitation of DAE1
with Gold Nanospheres
White Light Excitation of DAE1
with Gold Nanospheres
30
20
10
0
x10
-3
700650600550500450
Wavelength (nm)
0min
1min
2min
3min
0.6
0.4
0.2
0.0
Absorbance
650600550500450
Wavelength (nm)
parallel to
nano-rod
perpendicular
to nano-rod
Example of Non-Resonant
Excitation
• DAE1 being converted by the 400nm light
• Decreasing absorbance
• DAE1 not being converted by the 800nm light, in the absence of gold
nanoparticles
• Inconsistent absorbance change, likely due to fluctuation
• DAE1 being converted by 800nm light, in the presence of gold
nanoparticles
• Decreasing absorbance, caused by the increased electric field between
nanospheres
• DAE1 not being converted by the white light, used to take the
measurements
• Inconsistent absorbance change, likely due to fluctuation
0.1408
0.1404
0.1400
0.1396
Absorbance
20151050
Time(mins)
Absorbance at 573nm
0.140
0.136
0.132
0.128
Absorbance
12840
Time(mins)
Absorbance at 572nm
38.0
37.0
36.0
35.0
x10
-3
3.02.01.00.0
Time (mins)
Absorbance at 604nm 39.0
38.0
37.0
x10
-3
1086420
Time (mins)
Absorbance at 605nm