Takashi Chiba,[1] Asuka Fujii,[1] Katsuhiko Okuyama[2]

Presentation on theme: "Takashi Chiba,[1] Asuka Fujii,[1] Katsuhiko Okuyama[2]"— Presentation transcript:

1 Hyperconjugation in the S1 State of Substituted Toluene Probed by Infrared Spectroscopy
Takashi Chiba,[1] Asuka Fujii,[1] Katsuhiko Okuyama[2] [1] Graduate School of Science, Tohoku University [2] College of Engineering, Nihon University

2 Internal Rotation Potential in Fluorotoluene
Internal Rotation of CH3 as large amplitude motion Internal Rotation Potential in Fluorotoluene o-Fluorotoluene m-Fluorotoluene S0 S0 CH3 Rotation angle CH3 Rotation angle K.Okuyama et al. J. Phys. Chem. 1985, 89,

3 S1 S1 S0 S0 Internal Rotation of CH3 as large amplitude motion
Internal Rotation Potential in Fluorotoluene S1 S1 increase of the barrier height decrease of the barrier height o-Fluorotoluene m-Fluorotoluene S0 S0 What is the origin of these changes? CH3 Rotation angle CH3 Rotation angle K.Okuyama et al.　J. Phys. Chem. 1985, 89,

4 The theory of p*-s* hyperconjugation
Nakai has calculated the internal rotation potential and reproduced the experimental results p*-s* hyperconjugation s* Theory: hyperconjugation between the p* orbital on the aromatic ring and the s* orbital on methyl CH in LUMO crucially influences the internal rotation potential of o- and m-fluorotoluene [1] コメント：できれば図を先行させたい p* LUMO [1]H.Nakai , M.Kawai Chem.Phys.Lett 1999, 307 ,272–276

5 Our strategy to prove the p*-s* hypercomjugation
electron transfer from p* to s* in the S1 state π*-σ* hyperconjugation σ* decrease of bond strength of methyl CH Infrared spectroscopy in the S0 and S1 states コメント：緑色はよくないかも Methyl CH (stretch) π* S0 [cm-1] S1 Red-shift of bands? Fig.　LUMO [cm-1]

6 Purpose and Experiment
IR spectroscopy in the S0 and S1 states to prove the p*-s* hyperconjugation in o- and m-fluorotoluene m-fluorotoluene o-fluorotoluene(omit) Experiment: IR spectroscopy in the S0 state by the IR – UV method IR spectroscopy in the S1 state by the UV – IR method

7 IR – UV method UV – IR method IR spectroscopy in S0
monitoring of Ion Intensity monitoring of Ion Intensity =10ns =50ns =10ns

8 IR spectra of m-fluorotoluene
Methyl CH Phenyl CH wavenumber[cm-1] S1 Methyl CH Phenyl CH スケーリングファクターの決め方：o体のメチルＣＨの三本のピークに合わせる。( )　コメント：ただし、励起状態と基底状態で同一のファクターでよいかは念のため考える（多分ＯＫ。振動数計算は重さとポテンシャルだけで決まるはずだから。） wavenumber[cm-1] Splitting of the bands anharmonic coupling The methyl CH stretching bands show the red-shifts upon the electronic excitation This suggests the existence of the p*-s* hyperconjugation

9 Comparison between the experimental and simulated spectra of m-fluorotoluene
calculation level: S0 : HF/6-31G(d,p) S1 : CIS/6-31G(d,p) S0 (scaling factor ) p*-s* hyperconjugation was proposed by the calculation at these levels スケーリングファクターの決め方：o体のメチルＣＨの三本のピークに合わせる。( )　コメント：ただし、励起状態と基底状態で同一のファクターでよいかは念のため考える（多分ＯＫ。振動数計算は重さとポテンシャルだけで決まるはずだから。） wavenumber[cm-1] S1 The red-shift trend was reproduced [cm-1] This result supports that the observed red-shift comes from p*-s* hyperconjugation wavenumber[cm-1]

10 Comparison between the experimental and simulated spectra of m-fluorotoluene
wavenumber[cm-1] Only sym and antisym1 bands largely shift to low frequency Only CH bonds involved in the sym and antisym1 modes are influenced by the p*-s* hyperconjugation

11 Comparison between the experimental and simulated spectra of m-fluorotoluene
sym and antisym1 bands largely shift S1 スケーリングファクターの決め方：o体のメチルＣＨの三本のピークに合わせる。( )　コメント：ただし、励起状態と基底状態で同一のファクターでよいかは念のため考える（多分ＯＫ。振動数計算は重さとポテンシャルだけで決まるはずだから。） antisym2 band shift wavenumber[cm-1] Only sym and antisym1 bands largely shift to low frequency Only CH bonds involved in the sym and antisym1 modes are influenced by the p*-s* hyperconjugation

12 Normal modes of methyl CH in m- fluorotoluene
sym antisym1 antisym2 入れる情報は、 １モード。sym,asym1とasym2 の色分け。 ２Fの位置 ３超共役を受けるCH Only out of plane CH bonds contribute to the p*-s* hyperconjugation

13 Relation between the barrier change and hyperconjugation
m-Fluorotoluene S1 out of plane CH increase of the barrier height ? S0 CH3 Rotation angle How does the p*- s* hyperconjugation influence the internal rotation potential?

14 p*-s* hyperconjugation in m-fluorotoluene
Internal rotation potential S0 S1 out of plane CH コメント：先にポテンシャルの説明を。 CH3 Rotation angle Stabilization makes “well” Increase of barrier height LUMO p*-s* hyperconjugation is proved by IR spectroscopy!

15 Summary We observed the IR spectra in the S0 and S1 state of m-fluorotluene by the IR-UV and UV-IR method. In m-fluorotoluene, the p*-s* hyperconjugation was proved by IR spectroscopy The CH red-shift by p*-s* hyperconjugation was qualitatively reproduced by the HF/CIS calculations, which are primitive for analysis of the S0/S1 states. We omitted the results of o-isomer, but we also proved the existence of the p*-s* hyperconjugation in o- isomer by comparison between the observed and simulated IR spectra. コメント：メチルアニリンの図　cisの捉えられる範囲

16 ※質問の想定 １．パラ体は？ ２．トルイジンの結果は？ ３．非調和共鳴であるという根拠は？ ４．T1への遷移をしていないか？ ５．phyenlのところが合ってないのでは？ ６．モードは本当にローカルか？ ７．構造の変化は？ ８．奥山さんの実験について

17 apparatus digital delay pulse generator

18 About triplet (o-isomer)
S0(calc) S0(expt) S1 (expt) 計算によれば、S1とT1は10ns後に３：１の割合で存在する。 20ns後に6:5の割合で存在する。 ただし、phillipらの論文から計算されるS1の寿命は24nsであり、今回の実験においてdelayを20nsおいた場合のイオン化収量の低下はおよそ半分であった。したがって、S1以外のT1,S0の高振動励起状態からはイオン化しないと仮定すれば、計算の寿命とは合う。 そうすると、20ns後にイオン化しないのだから、T1に遷移していたとしても検出にはかからないので、いくらIRを吸っても（場合によってはNRIにかかるかもしれんが）dipにはならないことになる。 S1 (calc) T1 (calc)

19 About triplet (m-isomer)
S0(calc) S0(expt) S0 (expt) ※フルオロベンゼンおよびベンゼンのS1とT1の差はどちらもおよそ1eVほどある。 ※藤井・江幡のトルエン系のIR-UVのスペクトルの幅は3-5cm-1ほどであるが、今回のスペクトルはもっと幅がある。 スキャンスピードの問題にならないか？ S1 (calc) T1 (calc)

20 S0 S1 IR spectra in o-isomer [cm-1] [cm-1]

21 Normal modes of methyl CH in o- fluorotoluene
sym antisym1 antisym2 入れる情報は、 １モード。sym,asym1とasym2 の色分け。 ２Fの位置 ３超共役を受けるCH Only out of plane CH bonds contribute to the p*-s* hyperconjugation

22 HOMO in S0 state of m-isomer

23 LUMO in S0 state of m-isomer

24 HOMO in S1 state of m-isomer

25 LUMO in S1 state of m-isomer

26 HOMO in S0 state of o-isomer

27 LUMO in S0 state of m-isomer

28 HOMO in S1 state of o-isomer

29 LUMO in S1 state of o-isomer

30 internal rotation potential (Simulated by Nakai)
LUMO energy dependency along with q (Simulated by Nakai)

31 internal rotation potential (Simulated by Nakai)
Internal rotation potential (observed by Okuyama) S1 S1 S0 S0 CH3 Rotation angle CH3 Rotation angle

32 LIF spectrum in o-isomer
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

33 LIF spectrum in m-isomer
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

34 LIF spectrum in p-isomer
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

35 Internal rotation potential (o-isomer)
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

36 Internal rotation potential (m-isomer)
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

37 Internal rotation potential (p-isomer)
K.Okuyama et al.　J. Phys. Chem. 1985, 89,

38 Parameter on internal rotation potential

39 MPI spectra o- Fluorotoluene [cm-1] 37550 37600 m- Fluorotoluene
37400 37500 p- Fluorotoluene [cm-1] 36850 36950

40 vibration mode of m-isomser

41 vibration mode of o-isomser

42 IR spectra of p-isomer ・S0 ・S1

43 LUMO in S1 state of p-isomer

44 IR spectra in 0a1, 2e, 3a1 of S1 state (o-isomer)
Internal rotation potential in S1 state Free rotation Hindered rotation 0a1 2e 3a1

45 o-methyl aniline ・S0 2800 2900 3000 3100 ・S1 2800 2900 3000 3100

46 m-methyl aniline ・S0 2800 2900 3000 3100 ・S1 2800 2900 3000 3100

47 p-methyl aniline ・S0 2800 2900 3000 3100 ・S1 2800 2900 3000 3100

48 Broad background of IR spectra of methyl aniline in S1 state
transition to S2 state?

49 IR spectra in Toluene Toluene S0 Toluene S1
Phys. Chem. Chem. Phys., 2002, 4, 1537–1541

50 LUMO in S1 state of p-isomer

51 Charge distribution in S0 and S1 state(o-isomer)

52 Charge distribution in S0 and S1 state(m-isomer)

53 Bond length of CH bond (o-isomer)
Out-of-plain CH in-plain CH S0 S1 m-isomer Out-of-plain CH in-plain CH S0 S1