1. An Ongoing Study of Electronic Communication in Covalently v. Non-Covalently Bound Polyfluorene Systems 2015 International Symposium of Molecular Spectroscopy 06.24.15

2. Outline Fluorene and Polyfluorene Systems – Structure, Nomenclature, Methods Electronic Spectra Comparisons – Observables Ionization Potential Comparisons Summary

3. Motivation Examine the question, in a multi-chromophore system, what is the excitonic behavior of fluorene and polyfluorene systems as evidenced by their electronic spectra, as well as the ionization potentials of each sample?  Rathore, R., Abdelwahed, S. H.; Kiesewetter, M. K.; Reiter, R. C.; Stevenson, C. D.; J Phys Chem B. 2006, 110 (4), 1536-1540

4. Experimental Methods hν2hν2 hν1hν1 hν2hν2 hν1hν1 S0S0 S 1 /S 2 M +· + e - Can examine multiple observables with a single setup 2CR2PI

5. Fluorene Molecules Terminology – Convenient and easy shorthand to refer to both covalent and non- covalently linked polyfluorene systems “F n ” “F n H n ” H “(F1) n ” “(F) n ”

6. (F) n Series Electronic Spectra Wavenumbers

7. (F) n Ionization Potentials

8. (F1)n Series Electronic Spectra Wavenumbers “F1”

9. (F1) n Ionization Potentials

10. Covalent Electronic Spectra F1 F3 F2 F1 F2 F3

11. Ionization Potentials The ionization potentials of all the fluorene systems follow different trend lines most likely indicating unique geometries leading to different electronic behavior

12. Summary Polyfluorene systems are incredibly useful in serving as good model systems in the understanding of the ability and efficiency of π- stacked systems to transfer electrons and the excitonic interactions involved The difference in electronic spectra, ionization potentials, and excited state lifetimes (observables) would indicate that there is a co- facial, structural difference among the different polyfluorene systems that influence the efficiency of electron transfer

13. Acknowledgments  Prof. Scott Reid  Dr. Neil Reilly  Prof. Rajendra Rathore

14. Acknowledgments Thank You

15. Supplemental Slides

16. Additional F3 IP

17. (F) n Ionization Potentials

18. (F1) n Ionization Potentials

19. F2 with Simulation

20. “Fixed” Geometry Molecules Although mass spectrometry provides the advantage of being able to select molecules of specific masses, the downside remains to be the inability to select specific conformers Using molecules with fixed geometries eliminates the uncertainty created by having multiple minimum energy structures

21. Spiro-F2 Two fluorene molecules that are directly connected at the C9 position – No carbon connection like previous molecules Fixed about the tetrahedral center Spiro-F2 is a special case of the exciton splitting model due to the fact that the transition dipoles are perpendicular

22. 2-Color Spectra: Spiro F2

23. Helium v. Argon

24. R2PI (TOF-MS) Instrument Lightest ions arrive first KE = ½mv 2

25. 2CR2PI Instrument Chamber Detector Nozzle (Top-Down View) hν2hν2 hν1hν1 Pump

26. Exciton Coupling Small band splitting is observed based on the physical orientation of the molecule’s transition dipole The observed exciton splitting is ultimately dependent on three things: S1S1 S0S0 α θ r Kasha, M.; Rawls, H. R.; Ashraf El-Bayoumi, M.; “The Exciton Model in Molecular Spectroscopy”