1. Excited State Isomerization of a Stilbene Analog: Phenylvinylacetylene Josh J. Newby, Christian W. Müller, Ching-Ping Liu, Hsiupu D. Lee and Timothy S. Zwier 64 th International Symposium on Molecular Spectroscopy MF03 Department of Chemistry, Purdue University West Lafayette, IN 47907

2. Interest in Phenylvinylacetylene (PVA) J. Phys. Chem. A 106 (24): 5789-5796 (2002) J. Phys. Chem. A, 112(39), 9454 (2008) E-PVA TB02 Excitation and Emission Spectroscopy Z-PVA

3. Fluorescence and Absorbance UVD (absorption) LIF (fluorescence) LIF (fluorescence) UVD (absorption) Indicates the turn on of a fast, non-radiative process 1000 cm -1 600 cm -1 Relative Wavenumbers (cm -1 )

4. E/Z Isomerization 1A (S 0 ) 1B (S 1 ) 2A (S 2 ) trans (E) cis (Z) 1A´ (S 0 ) 1A ′ (S 1 ) 2A″ (S 2 ) trans (E) cis (Z) ? Is the loss in fluorescence due to cis/trans isomerization?

5. UV PUMP To diffusion pump UV Probe Reaction Channel Rxn quenched by expansion on  s timescales Pulsed Valve PumpProbe 60-80  s hν Ultraviolet Population Transfer (UVPT) in a time-of-flight mass spectrometer TOF into plane Determine product distribution via R2PI spectroscopy ? Reaction channel constrains the expansion allowing us to remove large amounts of internal energy from molecules.

6. Expt’l protocol: 1.Cool 2.Pump 3.Re-cool 4.Probe Ultraviolet Population Transfer (UVPT) S1S1 Z-PVA S 0 S1S1 E-PVA S 0 k iso k IC Pump ProbeCool k´ iso Hole-filling spectroscopy: Fix Pump, Tune Probe: See where the population went Population transfer spectroscopy: Tune Pump, Probe on E Watch population come into E from Z Z Z Z Z Z E E Z Z*Z* Z Z E*E* E*E* Z Z Z Cool EXCITE COOL PROBE Z*Z* Z COOL

7. Infrared-Population Transfer Spectroscopy WG13 J. Phys. Chem. A., 110 (12), 4133 (2006) J. Chem. Phys., 120 (1), 133 (2004) J. Chem. Phys., 120 (19), 9033 (2004) William H. James III

8. E-PVA Population Transfer Spectra E → Z E → E UVD E → Z E → E Scan Pump, Probe Z Measures population moved into a product well. Scan Pump, Probe E Measures how much population escapes the reactant well under collisional conditions UVD Measures how much population can be removed from the reactant well under “zero” collisional conditions

9. Z-PVA Population Transfer Spectra E → Z E → E Z → E hot bands Scan Pump, Probe E Measures population moved into a product well. Scan Pump, Probe Z Measures how much population escapes the reactant well under collisional conditions UVD Measures how much population can be removed from the reactant well under “zero” collisional conditions Z → Z UVD

10. Isomerization Quantum Yields Δν/cm -1 Φ r f (E) a Φ r EZ Δν/cm -1 Φ r f (Z) b Φ r ZE 01.00 5380.301.00 3260.670.77±0.237020.021.46±0.44 8150.900.90±0.279370.020.95±0.29 9311.260.86±0.269670.031.59±0.48 12140.190.96±0.2910600.011.54±0.46 12790.180.77±0.2311520.021.05±0.32 12920.130.81±0.2412230.021.19±0.36 14340.110.61±0.18 Take home: Isomerization is not the cause of the loss in fluorescence! (a) FL Quantum Yields relative to E-PVA 0 0 0 (b) FL Quantum Yields relative to Z-PVA 0 0 0

11. Double Bond Torsional PES

12. Fluorescence and Absorbance UVD (absorption) LIF (fluorescence) LIF (fluorescence) UVD (absorption) What is the non-radiative process? Relative Wavenumbers (cm -1 )

13. PVA Excited States ZPVA EPVA Angle (°) Relative Energy (eV) 1A′ 2A′ 3A′ 2A′ 3A′ 1A″ 2A″ 1A″ 1A′ π→π * π→σ * π→π * Close lying A″ states in both E and Z-PVA which correspond to the π→σ * excitation

14. Excited States Cont. M. Z. Zgierski and E. C. Lim Chem. Phys. Lett. 387 352 2004 T. Fujiwara, M. Z. Zgierski, and E. C. Lim, JPCA 112, 4736 2008 1,4-Bis(phenylethynyl)benzene

15. Conclusions UVPT has been developed to elucidate excited state dynamics E/Z Isomerization does NOT dominate in the excited state Isomerization most likely occurs on the ground state surface after interconversion PVA most likely departs initially excited A´ state to an A″ state via intersection No isomerization channel to naphthalene was observed

16. Acknowledgements Professor Timothy S. Zwier The Zwier Group William James WG13 Chirantha RodrigoMF05 Josh Sebree TB03 Evan Buchanan TB09 Zachary Davis James Redwine Ryan Muir Deepali Mehta Dr. Jaime Stearns Dr. Talitha Selby Dr. Jasper Clarkson Dr. V. Alvin Shubert Dr. Esteban Baquero Dr. Tracy LeGreve Dr. Nathan Pillsbury Dr. Ching-Ping Liu Dr. Christian Müller MF06, TB10 Dr. Mike Nix

17. PVA Excited States π→σ * π→π * A″A″ A′A′ π→σ * π→π * A′A′ A″A″

18. Fluorescence Quantum Yields ΦrfΦrf ΦrfΦrf (b) (a) Relative Wavenumbers (cm -1 )

19. x100 PVA PT compared to LIF x4x40 Isomerization is not the non-radiative feature that dominates. Relative Wavenumbers (cm -1 )

20. PVA fluorescence spectroscopy Loss in fluorescence but still show Frank-Condon Factors Isomerization? Internal Conversion? Intersystem Crossing? 000000 000000 000000 000000 25 1 0 26 1 0 19 1 0 26 0 1 25 0 1 19 0 1 24 0 1 29 0 1 29 1 0 20 0 1 (a) (b) LIF SVLF 0 0 0 + 1000 cm -1 0 0 0 + 600 cm -1

21. UVPT of Z-PVA to E-PVA X 50 TUNE Pump Probe E-PVA 0 0 0 LIF of Z-PVA UVPT of Z to E ‘Gain’ E-PVA population when resonant with a Z- PVA transition. T dn vib ~15 K Many hot bands of Z-PVA observed. T up vib ~50 K

22. Hole-filling of PVA Z to E and E to Z LIF of E-PVA LIF of Z-PVA Hole-filling Z to E LIF of E-PVA LIF of Z-PVA Hole-filling E to Z Pump Z PVA 0 0 0 +933 cm -1 TUNE ProbePump E PVA 0 0 0 +931 cm -1 TUNE Probe