1. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 1 DOUBLY HYDROGEN BONDED BIS-(4-HYDROXYPHENYL)METHANE DIMERS. Chirantha P. Rodrigo, Evan G. Buchanan, William H. James III and Timothy S. Zwier. Department of Chemistry, Purdue University, West Lafayette, IN 47907

2. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 2 BIS-(4-HYDROXYPHENYL)METHANE Monomers b4hpm structure.  Two para-cresol moieties connected through a methelyne group.  Four torsional degrees of freedom along PhOH, PhCH 2 coordinates. Giving rise to three possible conformational minima (and their enantiomers). Two symmetric (C 2 ) and one asymmetric (C 1 ) structures. C2C2 C1C1 Relative Energies: B3LYP/6-31+G(d) 0 cm –1 13 cm –1 7 cm –1 dd (down-down) uu (up-up)ud (or du) Gaussian 09 program suite.

3. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 3 b4hpm spectroscopy.  Two conformations observed in supersonic jet expansion. Both showed C 2 symmetry in ground and the first excited state.  Symmetric dd and uu structures observed in the gas phase.  Nearly identical UV and IR (torsional modes, CH stretch and OH stretch) spectra observed.  The states energy splitting is 132 cm –1 for both conformers. BIS-(4-HYDROXYPHENYL)METHANE Monomers 3100300029002800 Frequency / cm –1 intensity (arb. units) 368036603640 Frequency / (cm –1 ) 3656

4. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 4 b4hpm spectroscopy.  Two nearly isoenergetic conformations.  Nearly identical spectra in UV and IR.  Both conformations possess C 2 point-group symmetry in both ground and first excited states.  Two close lying excited states ( S 1 and S 2 ) which are separated by 132 cm –1. BIS-(4-HYDROXYPHENYL)METHANE Monomers Summary of Results and Conclusions dd (down-down) uu (up-up)

5. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 5 Supersonic Jet Expansion & Spectroscopic Methods: UV(R2PI, FES, SVLF) / UVHB / UVD / S 0 -RIDIRS Collisional cooling to zero-point vibrational levels Probe laser Probe 20 Hz UV Probe 20 Hz UV M + + e FES / SVLFR2PI UV-Depletion Δt=200 ns Pump 10 Hz UV Probe 20 Hz UV M + + e Δt=200 ns Pump 10 Hz UV Probe 20 Hz UV M + + e UV-Holeburning Δt=200 ns Pump 10 Hz IR Probe 20 Hz UV M + + e S 0 - RIDIRS

6. b4HPM Dimer Intensity / (arb. units) 3535035300352503520035150351003505035000349503490034850 Energy / (cm –1 ) b4HPM+(H 2 O) 1 Origin (b4HPM) 2 Origin Monomer Origin Fluorescence Excitation Spectrum in Monomer, Dimer and (H 2 O) 1 cluster region.

7. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 7 para-Cresol and Phenol Dimers Phenol Dimer  Fuke, K.; Kaya, K. Chem. Phys. Letters 1982, 91, 311.  Fuke, K.; Kaya, K. Chem. Phys. Letters 1983, 94, 97.  Weichert, A.; Riehn, C.; Brutschy, B. J. Phys. Chem. A 2001, 105, 5679.  Schmitt, M.; Böhm, M.; Ratzer, C.; Krügler, D.; Kleinermanns, K.; Kalkman, I.; Berden, G.; Meerts, W. L. Chem. Phys. Chem. 2006, 7, 1241. para-Cresol Dimer  Appel, I.; Kleinermanns, K. Ber. Bunsenges. Phys. Chem. 1987, 91, 140.  Yan, S.; Spangler, L. H. J. Phys. Chem. 1991, 95, 3915. A A D D

8. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 8 Formation of b4HPM Dimers Possible Dimer Formations.  O—H······O—H type Hydrogen bonded dimers  π ······H—O type Hydrogen bonded dimers Proton Donor : D Proton Acceptor : A AA DD DA AD

9. Electronic States AA DD DA AD Fuke, K.; Kaya, K. Chem. Phys. Letters 1983, 94, 97. b4HPM monomer spectroscopy A D

10. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 10 Conformational Search and Low Energy Structures MacroModel Conformational Search Energy levels calculated with MM (Amber*) Becke3LYP/6-31+G(d) Geometry Optimization (with zero-point correction) S1 S2 S20 ……………….. Singly H-bonded + π····H—O bonded stuctures, Doubly π····H—O bonded. Doubly hydrogen- bonded dimers. Relative Energy (kJ/mol) S9 S7 S14 S17 S13 S11 S15 S19 S12 S4 S6 S10 S21 ……………………… S2 S3 Singly H-bonded, π stacked Doubly bonded dimers. Gaussian 09 program suite.

11. D D A A D D A A A A D D D D A A D A D A 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 11 Low Energy Structures Becke3LYP/6-31+G(d) Geometry Optimization (with zero-point energy correction) The lowest energy dimer is formed out of two ud/du monomers. uu appears only in one dimer (S19) S9 (0 cm –1 ): C 2 (ud+du)S7 (135 cm –1 ) : C 1 (dd+ud)S13 (160 cm –1 ) : C 2 (dd+dd) S19 (255 cm –1 ) : C 2 (dd+uu)S11 (189 cm –1 ) : C i (ud+du)S17 (173 cm –1 ) : C 1 (dd+ud) NOTE A A D D

12. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 12 UV Depletion Spectroscopy Intensity / (arb. units) 357003560035500354003530035200351003500034900 Energy / cm –1 monomer S 1 -S 0 origin 393 816 450 156 644 116 B A C 6a 1 12 1

13. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 13 Conformer A Conformer A: UVD Intensity / (arb. units) 400350300250200150100500-50 Relative Energy from ZPL / cm –1 116 231 monomer origin Appel, I.; Kleinermanns, K. Ber. Bunsenges. Phys. Chem. 1987, 91, 140. para-cresol LIF para-cresol dimer: 108 cm -1 band assigned as intermolecular stretch fundamental. +116 cm –1 : S 2 Origin or low frequency vibrational fundamental? S2?S2?

14. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 14 Conformer A Conformer A: UVD and SVLF 6050403020100

15. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 15 Conformer B Conformer B: UVD and SVLF Intensity / (arb. units) 4003002001000 Energy from zero point level / (cm ) Origin SVLF Conformer B 9 17 23 33 40 48 56 65 72 102 UVD Conformer B 9 19 24 34 43 51 58 156 108

16. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 16 S 0 -RIDIRS: C—H Stretch

17. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 17 S 0 -RIDIRS: O—H Stretch

18. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 18 Conclusions & Future Work Intensity / (arb. units) 357003560035500354003530035200351003500034900 Energy / cm –1 393 816 450 156 644 116 B A Origins of other excited states (S 2, S 3 etc.) ? Ground state conformational assignments. Higher level theoretical calculations. 1.Functionals that better account for dispersion (M05-2X, ωB97xD etc.) 2.Excited state energies, geometries and frequencies.

19. 5/23/2015 International Symposium on Molecular Spectroscopy : 65th Meeting 19 Acknowledgment Advisor: Advisor: Prof. Timothy S. Zwier Zwier Research Group Dr. William H. James III (Post Doctoral fellow) Dr. Anna Gurtbelet (Post Doctoral fellow) Josh Sebree Evan Buchanan Zachary Davis James Redwine Deepali Mehta Jacob Dean Nathan Kidwell Computational Resources: Purdue ITapFunding: Department of Energy Past Group members Dr. Christian W. Müller Dr. Josh J. Newby Dr. Nathan R. Pillsbury Dr. Esteban E. Baquero Dr. Virgil A. Shubert Dr. Tracy A. LeGreve Dr. Jasper R. Clarkson Dr. Talitha Selby Dr. Ching-Ping Liu Collaborator : Dr. David F. Plusquellic Collaborator : Prof. Lyudmila Slipchencko