Ultraviolet Photodepletion Spectroscopy of Dibenzo-18-Crown-6-Ether Complexes with Alkali Metal Cations

Abstract

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M+-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35 450−37 800 cm−1. The lowest-energy band was tentatively assigned to be the origin of the S0-S1 transition, and the second band to a vibronic transition arising from the “benzene breathing” mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M+-DB18C6 increased from Li+ to Cs+. We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S0 and S1 states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories.

Ultraviolet photodissociation spectroscopy of cold, isolated adenine complexes with a potassium cation

“…The experimental set-up is described in detail elsewhere [32], and only a brief description is given below. A9 and KCl were purchased from Sigma-Aldrich and used without further purification.…”

Excited states of protonated DNA/RNA bases

“…Paul trap is mounted on the cold head of a cryostat (Coolpak Oerlikon) connected to a water-cooled He compressor. Helium as buffer gas is injected in the trap using a pulsed valve (General Valve) triggered 1 ms before the ions enter the trap as previously reported by Kamrath et al 18 The ions are trapped and thermalized at a temperature between 20 and 50 K through collisions with the cold buffer gas (see S.I. ).…”

Laser Spectroscopic Study of Cold Host–Guest Complexes of Crown Ethers in the Gas Phase

“…Recently, it has been demonstrated that the laser spectroscopic study of cold gas-phase CEs and their complexes, not only for ionic species [32][33][34][35][36][37][38][39][40][41][42][43] but also the neutral species, [44][45][46][47][48][49][50][51][52] can provide A laser spectroscopic study on the structure and dynamics of cold host-guest inclusion complexes of crown ethers (CEs) with various neutral and ionic species in the gas phase is presented. The complexes with neutral guest species are formed by using supersonic free jets, and those with ionic species are generated with electrospray ionization combined with a cold 22-pole ion trap.…”