Electronic spectra of calix[n]arene and its van der Waals clusters in supersonic jets T. Ebata, k. Nishimoto, N. Hontama, and Y. Inokuchi Chemistry Department, Hiroshima University, Japan ○ Cyclodextrine ○ Crown-ether ○ Calixarene ○ Biomolecule Key interaction: noncovalent interaction. However: The binding energy of the interaction is comparable to the thermal energy at room temperature. → Limited information of averaged structure Abilities of 1.Transfer metal ion between two different phases 2.Discrimination of chirality of chiral molecule 3.Photochemical switch Purpose: Detailed study on guest-host interaction leading molecular recognition.

○ Four phenol molecules are connected by methylene groups. ○ The molecule can encapsule many type of molecule(s) through van der Waals (or H-bond) interaction. Study on encapsulation of guest-molecule(s) by calixarene Calix[4]arene (C4A) Electronic states ○ Four electronic states are degenerated (Lowest electronic state) ○ Four OH group are strongly H-boned (IR spectrum) ○ Encapsulation of different kind of atoms and molecules. (Reveal the intrinsic nature of encapsulation)

How do we obtain the supersonic jet of calix[n]arene Melting point of L-Phe is 315 ℃。 It is necessary to vaporize the sample without thermal decomposition. (1) Heating nozzle : Use of metal-free nozzle (2) Laser ablation nozzle: Difficulty of shot-to-shot stabillity to obtain the UV and IR spectra. Heating nozzle Laser ablation 試料をロッドに 吹き付けておく

Electronic states of C4A 1B1E1A1A1B1E1A1A μzμz μ xy Dipole transition under C 4 symmetry weak 0,0 band Upper state will be the 1 A state. Transition moments are tilted from the xy-plane. Strong vibronic bands at ～ 35540cm -1 and no overtone band The vibronic bands may be appeared through the vibronic coupling with 1 E state. LIF スペクトル 0,0 バンド Z Transition moment xy 0.0 band ? ? ?

Calix[4]arene(C4A)-M clusters C4A C4A-Ar n C4A-(N 2 ) n C4A-(CH ４ ) n C4A-(H 2 O) 1 0, C4A can easily form van der Waals clusters

Electronic spectra of Calix[4]arene-Ar n clusters calix[4]arene-(Ar) n A partial pressure of Ar as low as 0.4 % is large enough for complete clustering !

Red-shift of the 0,0 band Structure of Calix[4]arene - Ar n,Ne n clusters Van der Waals Interaction with four phenol molecules

Red-shift of C4A-M n=1 vs. polarizability Ne Ar N2N2 CH 4  ( Å 3 ) ◎ For Ne and Ar as a guest, the red-shift is in proportional to polarizability. ◎ On the other hand, the red-shift is very sensitive to the orientation of the guest molecule. Red-shift of the 0,0 band of C4A-Ne n, -Ar n, -N 2n Structure of Calix[4]arene - Ar n Ne n, (N 2 ) n clusters Large difference

Calix[4]arene(C4A)-M clusters C4A C4A-Ar n C4A-(N 2 ) n C4A-(CH ４ ) n C4A-(H 2 O) 1 0, C4A can easily form van der Waals clusters

Ab initio calculated structure of C4A-H 2 O ( HF/3-21G ) 0 cm cm cm cm -1

Most stable structureCalculated IR spectrum Structure of Calix[4]arene-(H 2 O) 1 Water is involved in the H-bonding network of C4A Free OH stretch of water IR-UV double resonance spectroscopy is in progress

Encapsulation ability of C4A Partial pressure of Ar Calix[4]arene-Ar n 2,6-dimethylphenol-Ar n 25 Ar/He(%) % He No van der Waals band ◎ C4A has a high ability of encapsulating atom and molecule ◎ How large is the binding energy ?

LIF 1+1’ REMPI Time-of-Flight Binding energy of C4A-(Ar) n IP 0 <7.87 eV Preliminary results h 2 =355 nm C4A-Ar 1 (0,0) C4A-Ar 2 (0,0)

C4AC5A Summary 1.Laser Spectroscopy has been successfully applied to jet-cooled Calix[4]arene(C4A). 2.S 1 state is 1 A,under C 4 point group. 3.S 1 state is strongly vibronically coupled with upper S 2 ( 1 E) state. 4.C4A has a high ability of encapsulating a hydrophobic molecule. 5.The electronic spectrum of C4A is very sensitive to the anisotropy of guest molecule. C4A –Ar ←→ C4A –N 2 Future work 1.Determination of binding energy inside/outside the cavity. 2.Elucidation of encapsulation structure of various guest molecule(s). 3.Extension to larger size calixarene(C5A, C6A) and different type of calixarene (resolcin arene).