Geometric and Electronic Structures of Dibenzo-15-Crown-5 Complexes with Alkali Metal Ions Studied by UV Photodissociation and UV–UV Hole-Burning Spectroscopy

Abstract

We measure UV photodissociation (UVPD) and UV-UV hole-burning (HB) spectra of dibenzo-15-crown-5 (DB15C5) complexes with alkali metal ions, M·DB15C5 (M = Li, Na, K, Rb, and Cs), under cold (∼10 K) conditions in the gas phase. The UV-UV HB spectra of the M·DB15C5 (M = K, Rb, and Cs) complexes indicate that there is one dominant conformation for each complex except the Na·DB15C5 complex, which has two conformers with a comparable abundance ratio. It was previously reported that the M·(benzo-15-crown-5) (M·B15C5, M = K, Rb, and Cs) complexes each have three conformers. Thus, the attachment of one additional benzene ring to the crown cavity of benzo-15-crown-5 reduces conformational flexibility, giving one dominant conformation for the M·DB15C5 (M = K, Rb, and Cs) complexes. In the UVPD spectra of the K·DB15C5, Rb·DB15C5, and Cs·DB15C5 complexes, the S-S and S-S transitions are observed independently at different positions with different vibronic structures. The spectral features are substantially different from those of the K·(dibenzo-18-crown-6) (K·DB18C6) complex, which belongs to the C point group and exhibits exciton splitting with an interval of 2.7 cm. The experimental and theoretical results suggest that in the M·DB15C5 complexes the two benzene rings are not symmetrically equivalent with each other and the S-S and S-S electronic excitations are almost localized in one of the benzene rings. The electronic interaction energy between the two benzene chromophores is compared between the K·DB15C5 and K·DB18C6 complexes by quantum chemical calculations. The interaction energy of the K·DB15C5 complex is estimated to be less than half of that of the K·DB18C6 complex (∼30 cm) due to less suitable relative angles between the transition dipole moments of the two benzene chromophores in K·DB15C5.

Selective Probing of Potassium Ion in Solution by Intramolecular Excimer Fluorescence of Dibenzo‐Crown Ethers

“…Vertical electronic transition energies obtained by the time‐dependent density functional theory (TD‐DFT) calculations are also displayed in Figure with blue bars. As demonstrated in the previous reports, the calculation level used in this study (M05‐2X/6‐31+G(d)) can provide reasonable results for the geometric and electronic structures of benzo‐CE complexes ,. For the K + ⋅ DB21C7 complex, the most stable structure (K‐A in Figure c) has an open conformation with benzene rings distant from each other.…”

“…The spectra of the K + ⋅ DB15C5 and K + ⋅ DB18C6 complexes exhibit well‐resolved sharp vibronic bands. The K + ⋅ DB15C5 complex shows two progressions in the 36600–37000 cm −1 region; one shows an extensive and intense progression around 36700 cm −1 , and the other has a strong band at 36839 cm −1 followed by several vibronic bands on the high frequency side . We assigned these progressions to the S 1 –S 0 and S 2 –S 0 transitions of a single conformer .…”

“…In the present study, we investigate the geometric and electronic structures of dibenzo‐21‐crown‐7 and dibenzo‐24‐crown‐8 complexes with potassium ion, K + ⋅ DB21C7 and K + ⋅ DB24C8. We measure UV spectra of the complexes under cold (∼10 K) gas‐phase conditions, and compare the results with those of K + ⋅dibenzo‐15‐crown‐5 (K + ⋅ DB15C5) and K + ⋅ DB18C6 complexes, which were previously reported ,. We examine the effects of the crown size and conformation on the electronic interaction for these complexes.…”

“…In the UVPD spectrum of the K + ⋅ DB18C6 complex, a strong origin band is found at 36415 cm −1 , and vibronic bands show an exciton splitting with an interval of ∼2.7 cm −1 , which indicates that a weak electronic interaction occurs between the two benzene chromophores . Figures a and 2b show the structure with the highest occupied molecular orbital (HOMO) and second highest occupied molecular orbital (HOMO‐1) of the K + ⋅ DB15C5 (K‐A) and K + ⋅ DB18C6 (K‐a) complexes determined in the previous studies ,. Molecular orbitals (MOs) that contribute the most to the S 1 –S 0 and S 2 –S 0 transitions are shown in the Supporting Information.…”

“…Figure displays UV photodissociation (UVPD) spectra of the K + ⋅ DB15C5, K + ⋅ DB18C6, K + ⋅ DB21C7, and K + ⋅ DB24C8 complexes in the 35900–37400 cm −1 region (red curves). The spectra of the K + ⋅ DB15C5 and K + ⋅ DB18C6 complexes are taken from our previous reports ,. The spectra of the K + ⋅ DB15C5 and K + ⋅ DB18C6 complexes exhibit well‐resolved sharp vibronic bands.…”