Laser Spectroscopic Study of Encapsulation Complexes in the Gas Phase : Molecular Level Understanding of the Encapsulation Mechanism of Host-Guest Complexes

Laser spectroscopic study has been carried out for host-guest encapsulation complexes formed in supersonic jets and electrospray ionization cold 22 ion trap. The examined hosts include benzene-substituted 18-crown-6-ethers and calix[4]arene, and for the guest species rare gas atoms, neutral molecules and alkali metal cations have been chosen. Various laser spectroscopic methods are applied: for the neutral complexes the electronic spectra are observed by laserinduced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultravioletultraviolet hole-burning (UV-UV HB) spectroscopy. The vibrational spectra are observed by infrared-ultraviolet double resonance (IR-UV DR) and fragment detected infrared photodissociation (IRPD) spectroscopy. For the ionic complexes, ultraviolet photodissociation (UVPD) and IR-UV DR spectroscopy has been applied. The obtained results are analyzed by density functional theory and first principles electronic structure calculations. We discuss how the host molecule changes its conformation or which conformer is preferred for forming stable encapsulation complex as well as the key interactions, leading to the molecular recognition