Photo-Induced Assembly of Spiropyran Polymers with Different

Metal Ions Hillary Straub1,2, Larisa Florea1, Dermot Diamond1 1 Insight Centre for Data Analytics, National Centre for Sensor

Research, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland

2Department of Chemistry, University of Kansas, Lawrence, USA

Background

Me2+

Spiropyrans are photochromic molecules that can be reversibly switched between the spiro form (SP) and the merocyanine form (MC) using light of appropriate wavelengths.

1

Background and Applications

2

Thermoresponsive polymers incorporating spiropyran have been used in light-induced aggregation.

Photo-induced conformational changes have been observed with spiropyrans functionalized on polypeptides.

DOI: 10.1039/c3cs60181a

Aggregation of Spiropyran Polymers with Metal Ions

Me2+ Me2+ Me2+

+ + + +

+ + +

+ +

+

-

- - -

- -

- -

-

-

3

Synthesis of the Monomer

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

250 300 350 400 450 500 550 600 650 700 750

Abso

rban

ce (a

.u)

Wavelength (nm)

Monomer-UV

Monomer-WL

4

Synthesis of Polymer

n

5

Spiropyran Polymer without Me2+

6

Photo-Induced Me2+ Aggregation Explore photo-induced aggregation by

varying the given parameters: solvent environment Me2+ Identity The ratio of Me2+ compared to the number of

MC units in the Polymer chain The length of the polymer chain

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75 Length Polymer Cu2+:MC

Units Ratio of DMF (1mg/mL) to water

1:1 1:2.3 1:4 1:9 1:2 Prior UV UV 1:4 Prior UV 1:8 UV UV

1:16 UV 1:32

Results: Cu2+ Induced Aggregation

300 Length Polymer Cu2+:MC

Units Ratio of DMF (1mg/mL) to water

1:1 1:2.3 1:4 1:9

1:2 Prior UV UV UV

1:4 Prior UV UV

1:8 Prior UV

1:16 UV

1:32 UV

1:64 UV

The longer chain polymer shows a larger range of results. Both polymer chain lengths demonstrate that as the concentration of polymer decreases and the amount of water in the sample increases, the aggregation is limited or unseen.

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The Affect of Water in the Sample Vs. the Affect of the Polymer Concentration

300 Length Polymer Cu2+:MC

Units Ratio of DMF to water

(amount of Polymer in 1 mL Sample)

1:1 (.5mg) 1:9 (.5mg) 1:9 (.1mg)

1:2 Prior Prior UV

1:4 Prior Prior

1:8 Prior Prior

1:16 UV UV

1:32 UV UV

1:64 UV

Although water has a slight affect on the aggregation of the samples, the concentration of the polymer in the sample is shown to be a more important factor in the aggregation of samples in ratios of DMF and water.

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UV-Vis Data

-0.025

0.025

0.075

0.125

0.175

300 350 400 450 500 550 600 650 700 750 800

Abso

rban

ce (a

.u.)

Wavelength (nm)

Polymer+White Light

Polymer+UV

Polymer+Cu-preUV

Polymer+Cu-postUV

13

Results: Testing Different Metal Ions 75 Length Polymer

1:1 DMF:water (.5mg PMR in 1mL Sample)

Me2+:MC units Cu2+ Co2+ Ni2+ Zn2+ Ca2+

1:2 Prior UV UV UV 1:4 Prior UV 1:8 UV UV

1:16 UV 1:32

300 Length Polymer

1:1 DMF:water (.5mg PMR in 1mL Sample)

Me2+ : MC units Cu2+ Co2+ Ni2+ Zn2+ Ca2+

1:2 Prior UV UV UV Prior 1:4 Prior UV

UV 1:8 Prior UV UV

1:16 UV 1:32 UV

1:64 UV

**Copper was the only metal ion to cause photo-induced aggregation in samples with an increasing amount of water and decreasing concentration of polymer.

**Nickel and Zinc samples also showed aggregation in the ratio 1:2.3 of DMF : water, but not in samples with lower concentration of polymer. Red indicates ratios that have yet to be tested.

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De-aggregation

Me2+

Me2+, UV - Me2+, White light

• De-aggregation could not be achieved by photo-irradiation • Irradiation with white light caused the aggregates to turn from

purple to white • Similar results were obtained with all of the metal ions studied

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SEM Images

Left: 1:1 DMF: Water with 1:4 Cu2+:MC units; Top Right: 1:1 DMF: Water with 1:2 Zn2+:MC units; Bottom Right: 1:1 DMF: Water with 1:2 Ni2+:MC units. SEM images of aggregates acquired 30 July 2014

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Conclusions The length of the polymer chain facilitates in the

aggregation of the samples A higher ratio of organic solvent compared with water

showed a larger range of results, caused by the higher amounts of polymer in the samples.

Lower ratios of metal ion: MC units cause aggregation; The samples with higher amounts of polymer in the samples and the samples with the metal ions with higher binding affinities showed successful aggregation with lower ratios of metal ions: MC units

Successful aggregation was seen in the metal ions with less binding affinity

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Acknowledgements

Science Foundation Ireland under the Insight initiative, grant SFI/12/RC/2289

Hamilton Undergraduate Research Scholarship 2014.

University of Kansas

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