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

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

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),

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

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 ”

(F) n Series Electronic Spectra Wavenumbers

(F) n Ionization Potentials

(F1)n Series Electronic Spectra Wavenumbers “F1”

(F1) n Ionization Potentials

Covalent Electronic Spectra F1 F3 F2 F1 F2 F3

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

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

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

Acknowledgments Thank You

Supplemental Slides

Additional F3 IP

(F) n Ionization Potentials

(F1) n Ionization Potentials

F2 with Simulation

“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

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

2-Color Spectra: Spiro F2

Helium v. Argon

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

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

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”