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

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, 5617-5625

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, 5617-5625

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

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]

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

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

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。(20150702)　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

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 0.9153) 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。(20150702)　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]

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

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。(20150702)　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

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

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?

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!

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

※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

apparatus digital delay pulse generator

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)

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)

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

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

HOMO in S0 state of m-isomer

LUMO in S0 state of m-isomer

HOMO in S1 state of m-isomer

LUMO in S1 state of m-isomer

HOMO in S0 state of o-isomer

LUMO in S0 state of m-isomer

HOMO in S1 state of o-isomer

LUMO in S1 state of o-isomer

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

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

LIF spectrum in o-isomer K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

LIF spectrum in m-isomer K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

LIF spectrum in p-isomer K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

Internal rotation potential (o-isomer) K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

Internal rotation potential (m-isomer) K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

Internal rotation potential (p-isomer) K.Okuyama et al.　J. Phys. Chem. 1985, 89, 5617-5625

Parameter on internal rotation potential

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

vibration mode of m-isomser

vibration mode of o-isomser

IR spectra of p-isomer ・S0 ・S1

LUMO in S1 state of p-isomer

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

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

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

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

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

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

LUMO in S1 state of p-isomer

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

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

Bond length of CH bond (o-isomer) Out-of-plain CH in-plain CH S0 1.08496 1.08321 S1 1.08938 1.08048 m-isomer Out-of-plain CH in-plain CH S0 1.08578 1.08330 S1 1.08942 1.08322