Cage effects on conformational preference and photophysics in the host–guest complex of benzenediols with 18-Crown-6

Abstract

The conformational preference and modification of photophysics of benzenediols, namely hydroquinone (HQ), resorcinol (RE) and catechol (CA), upon host-guest complex formation with 18-Crown-6 (18C6) have been investigated, under supersonically jet-cooled conditions. Laser induced fluorescence (LIF) and UV-UV hole-burning spectra indicate the presence of two conformers for HQ and RE and one conformer for CA. On the other hand, the number of isomers is reduced to one in the 18C6·HQ and 18C6·RE complexes, while the 18C6·CA complex has three stable isomers. The IR spectra of the OH stretching vibration reveal that the two OH groups are H-bonded in 18C6·CA and 18C6·RE. In 18C6·RE, RE adopts the highest energy conformation in the bare form. In 18C6·HQ, the H-bonding of one OH group affects the orientation of the other OH group. The complex formation changes the photophysics of the S1 state of the benzenediols in a different manner. In our previous work, we reported a remarkable S1 lifetime elongation in 18C6·CA complexes; the S1 lifetime of CA is elongated more than 1000 times longer (8 ps → 10.3 ns) in 18C6·CA (F. Morishima et al., J. Phys. Chem. B, 2015, 119, 2557-2565), which we called the "cage effect". In 18C6·RE, the increase of S1 lifetime is moderate: 4.0 ns (monomer) → 10.5 ns (complex). On the other hand, the S1 lifetime of HQ is shortened in 18C6·HQ: 2.6 ns (monomer) → 0.54 ns (complex). Density functional theory (DFT) calculations suggest that these behaviors are related to the S1 ((1)ππ*)-(1)πσ* energy gap, the character of the S2 state and the symmetry of benzenediol. These experimental results clearly show the potential ability of 18C6 to control the conformation and modification of the electronic structure of guest species.

Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules

“…Depending on the ortho ( o ), meta ( m ) or para ( p ) position of the substituent on the phenol ring with respect to the OH moiety, the associated dynamics is apparently quite different. In general, the substitution on the meta ‐ or para ‐position of phenol does not seem to be much influential on the OH bond cleavage dynamic in terms of the tunneling rate and the excess energy disposal dynamics, 116,120,138,142,143,145–151 except the presence of the additional chemical bond cleavage channels introduced especially for the bromo‐ or iodo‐phenol, for example 137,141 . The ortho ‐substitution, on the other hand, gives rise to the substantial changes in the whole reaction dynamics.…”

“…Chemical derivatives of phenol including fluorophenol, chlorophenol, bromophenol, iodophenol, or methylphenol (cresol) have been much studied to date 100,116–121,136–151 . Depending on the ortho ( o ), meta ( m ) or para ( p ) position of the substituent on the phenol ring with respect to the OH moiety, the associated dynamics is apparently quite different.…”

“…The state‐specific S 1 lifetime of catechol was reported to be 7 or 11 ps at the S 1 origin and first quantum of the OH torsional mode, respectively, 117,118,148 and it has been ascribed to the nonplanarity of the S 1 catechol at its minimum energy 162,163 . The S 1 lifetime of hydroquinone had been reported to be 2.7–3.0 ns, 145,148,149 whereas that of resorcinol seems to be scattered in the literature, giving the lifetime in the 2.7–4.5 ns range 143,145,148,149 . When benzenediols are complexed with a single water molecule, the S 1 relaxation dynamics is significantly influenced by the modified potential energy surfaces especially in the vicinity of the ππ*/πσ* curve crossing regions 148,149 .…”

Combined spectroscopic studies on post-functionalized Au25 cluster as an ATR-FTIR sensor for cations

“…[16][17][18] Crown ethers have been applied as complexing agents for primary and secondary alkylammonium ions, [19][20][21] some transition metal ions, 22 lanthanides and actinides 23 and for small molecules such as urea, thiourea, acetonitrile and nitro compounds. 24,25 These neutral synthetic heterocyclic compounds are of interest due to their powerful cation binding properties in areas such as host-guest chemistry and in the construction of well-dened supramolecular assemblies. Crown-based sensors designed for cation recognition with high selectivity and a variety of responses can be developed by the attachment of a chromophore, uorophore or luminophore into the crown framework.…”

Crown ether-appended calix[2]triazolium[2]arene as a macrocyclic receptor for the recognition of the H2PO4−anion

“…The increased size of the crown ether enabled the recognition of H2PO4 − having a larger size and complex tetrahedral shape compared to other anions through an induced-fit recognition mechanism. 22 We also conducted DFT calculations to gain insight into the binding interactions between the calix[2]triazolium[2]arenes and H2PO4 − . The geometries of 7 (Fig.…”