A Study of 4,4 ΄ -Dimethylaminobenzonitrile by Chirped-Pulsed Fourier Transform Microwave Spectroscopy Ryan G. Bird, Valerie J. Alstadt, and David W. Pratt University of Pittsburgh Justin L. Neill and Brooks H. Pate University of Virginia

Prelude to Charge Transfer DMABN is widely known model for excited state charge transfer Charge transfer facilitated by twisting amino nitrogen Determine electronic density around amino nitrogen using quadrupole coupling terms DMABN = 2 nitrogen nuclei – Simplified model; DMA = 1 nucleus E. Lippart, W. Lüder, and H. Boos, in the Proceedings of the 4th International Meeting on Advances in Molecular Spectroscopy (1959), A. Mangini, ed., Pergamon Press, Oxford, 1962, pgs

CP FTMW Spectrometer MW Synthesizer Arbitrary Waveform Generator Fourier Transform Free Induction Decay Chirped Pulse 240 MHz 500 MHz Digitizer (10 Gs/s)

Spectrum of N,N΄-Dimethylaniline avg ~500 MHz CP

Inversion of DMA 5 05 ← avg 10 MHz CP

Rotational Constants DMA This workLister 1 mp2/6-31+g(d) A(0 + ) (MHz) (103) B(0 + ) (MHz) (4) C(0 + ) (MHz) (3) A(0 - ) (MHz) (119) B(0 - ) (MHz) (5) C(0 - ) (MHz) (5) ΔI (amu Å 2 ) Lines95 1 Cervellati, R.; Borgo, A. D.; Lister, D. G. Journal of Molecular Structure 1982, 78,

Barrier to Inversion Aniline 1 N-methylaniline 1 N,N-dimethylaniline Inversion angle (φ)37~2022 V 2 barrier (cm -1 ) Cervellati, R.; Esposti, A. D.; Lister, D. G.; Palmieri, P. Journal of Molecular Structure: THEOCHEM 1985, 122, ΔE = cm -1 I is the integrated peak area g is the statistical weight F = ћ 2 /2I r I r is the reduced moment of inertia of the inversion motion

N,N΄-Dimethylaminobenzonitrile 2 – 8 GHz 190,000 avg 9 GHz CP 6 – 18 GHz 10,000 avg ~500 MHz CP

DMABN Constants This workEndo 1 LIF 2 M052x A (MHz)3469.2(9) B (MHz) (2) C (MHz) (2) ΔI (amu Å 2 ) Lines293 1 Kajimoto, O.; Yokoyama, H.; Ooshima, Y.; Endo, Y. Chemical Physics Letters 1991, 179, Nikolaev, A. E.; Myszkiewicz, G.; Berden, G.; Meerts, W. L.; Pfanstiel, J. F.; Pratt, D. W. Journal of Chemical Physics 2005, 122, 1-10.

Quadrupole Splitting in DMABN 2 – 8 GHz6 – 18 GHz 3 13 ← ←8 08

Amine Quadrupole Coupling CompoundAniline 1 DMADMABN Amine N χ aa (MHz)2.34(6)2.58(3)2.54(33) χ bb (MHz)1.86(6)2.80(6)2.80(13) χ cc (MHz)-4.20(6)-5.39(6)-5.33(13) Inversion Angle (deg) Hatta, A.; Suzuki, M.; Kozima, K. Bull. Chem. Soc. Jap. 1973, 46, Lone pair density Inversion angle

Hyperconjugation H H H N - + C C π-π donation N - +

Nitrile Quadrupole Coupling DMABNBenzonitrile 1 Ethyl Cyanide 2 Nitrile N χ aa (MHz)-4.11(30) (36)-3.309(33) χ bb (MHz)2.40(13)2.2886(11)1.265(13) χ cc (MHz)1.71(13)1.9488(11)2.044(20) 1 Wohlfart, K.; Schnell, M.; Grabow, J. U.; Küpper, J. Journal of Molecular Spectroscopy 2008, 247, Li, Y. S.; Harmony, M. D. The Journal of Chemical Physics 1969, 50, C N π-π donation

Townes and Dailey Populations 1 Aniline 2 DMADMABN χ zz (MHz) χ xx (MHz) χ yy (MHz) NzNz NxNx NyNy X Y 1 Townes, C. H.; Dailey, B. P. The Journal of Chemical Physics 1949, 17, Lister, D. G.; Tyler, J. K.; Høg, J. H.; Larsen, N. W. Journal of Molecular Structure 1974, 23,

Aniline → DMA → DMABN Decrease in inversion angle and increase in amine χ cc coupling term Caused by increase in electronic density around amine nitrogen Electronic density stabilized through hyperconjugation Increased density facilitates charge transfer Quadrupole terms of excited state??

Acknowledgements Pratt Group:Pate Group: Dr. David PrattDr. Brooks Pate Justin Young Justin Neill A.J. FleisherMatt Muckle Phil MorganDaniel Zaleski Jessica Thomas Casey Clements

Quadrupole Coupling CompoundAniline 1 DMADMABNBenzonitrile 2 Ethyl Cyanide 3 Amine N χ aa (MHz)2.34(6)2.58(3)2.54(33) χ bb (MHz)1.86(6)2.80(6)2.80(13) χ cc (MHz)-4.20(6)-5.39(6)-5.33(13) Nitrile N χ aa (MHz)-4.11(30) (36)-3.309(33) χ bb (MHz)2.40(13)2.2886(11)1.265(13) χ cc (MHz)1.71(13)1.9488(11)2.044(20) 1 Hatta, A.; Suzuki, M.; Kozima, K. Bull. Chem. Soc. Jap. 1973, 46, Wohlfart, K.; Schnell, M.; Grabow, J. U.; Küpper, J. Journal of Molecular Spectroscopy 2008, 247, Li, Y. S.; Harmony, M. D. The Journal of Chemical Physics 1969, 50,

119° 6° Structures DMABN DMA 113° 22°