1. Vibrational, Electronic, and Fluorescence Spectra and Ab Initio Calculations of 1,4-Benzodioxan (14BZD) Juan Yang, Martin Wagner, Daniel Autrey, and Jaan Laane Department of Chemistry, Texas A&M University June 21, 2005

2. Outline 1,4-Benzodioxan and Related Molecules Ab Initio Calculations IR and Raman Spectra of 14BZD UV, FES, and SVLF Spectra of 14BZD Conclusions

3. cyclohexene 2,3-dihydro-1,4-dioxin 1,4-Benzodioxan and Related Molecules x — ring-bending coordinate; τ— ring-twisting coordinate. tetralin 1,4-benzodioxan (TET) (14BZD) The two-dimensional potential energy surface of cyclohexene.

4. Tetralin and 1,4-Benzodioxan Calculated optimized structures for TET and 14BZD in electronic ground state from MP2/cc-pVTZ calculations. Twist Angles 31.4º 30.1º Barriers to planarity (cm -1 ) 4809 4093

5. The Lowest Frequency Vibrations The four lowest frequency vibrations for TET and 14BZD.

6. 14BZD Vapor IR Spectrum Vapor infrared spectrum of 14BZD vapor (top) compared to the calculated DFT spectrum with a scaling factor of 0.985 for frequencies less than 1700 cm -1 and 0.964 for frequencies greater than 2800 cm -1 (bottom).

7. Vapor Raman spectrum of 14BZD vapor (top) compared to the calculated DFT spectrum with a scaling factor of 0.985 for frequencies less than 1700 cm -1 and 0.964 for frequencies greater than 2800 cm -1 (bottom). 14BZD Vapor Raman Spectrum

8. Low-frequency Raman spectrum of 14BZD vapor (250°C). 14BZD Low-Frequency Vapor Raman Spectrum

9. FES and SVLF Techniques Transitions in fluorescence excitation spectroscopy (left) and single vibronic level fluorescence spectroscopy (right). FES SVLF

10. 14BZD UV and Jet-Cooled FES Spectra Ultraviolet absorption spectrum (top) and jet-cooled fluorescence excitation spectrum (bottom) of 14BZD.

11. 14BZD UV and SVLF Spectra Ultraviolet absorption spectrum (top) and single vibronic level fluorescence spectra with excitation of 0 0 0 at 35,564.50 cm -1, 25 0 1 at 35,704.1 cm -1 and 25 0 2 at 35,842.8 cm -1 (bottom) of 14BZD.

12. 2-D PE Function of 14BZD Experimental and computed (in parenthesis) energy levels (cm -1 ) and two-dimensional potential energy function of the ring-bending coordinate θ and the ring-twisting coordinate τ for the electronic ground state of 14BZD. Barrier to planarity: ~2200 cm -1

13. Conclusions The potential energy surface for 14BZD can be described as a two-dimensional function of the ring-bending coordinate θ and the ring-twisting coordinate τ. Mid-IR, Raman, UV absorption, FES and SVLF spectra of 14BZD were recorded and assigned. The energy minima for 14BZD are at twist conformations with high barriers to planarity. The resulting first few energy levels for the ring-bending and ring-twisting vibrations in the electronic ground state were assigned. They agreed very well with computed energy levels.

14. Acknowledgement$ National Science Foundation Robert A. Welch Foundation Texas Advanced Research Program