Aromatic Molecules in Restricted Geometries:  Pyrene Excimer Formation in an Anchored Bilayer

Abstract

The galleries of an anionic clay, Mg-Al Layered Double Hydroxide (Mg-Al LDH) have been functionalized by intercalating the anionic surfactant do-decyl sulfate. Within the galleries, the alkyl chains of the surfactant adopt a bilayer structure with the sulfate headgroup anchored to the inorganic sheet. Pyrene molecules have been solubilized in the anchored bilayer by partitioning from polar solvents. The presence of pyrene molecules induces conformational disorder in the alkyl chains of the bilayer and more importantly inhibits the rotational disordering motion of the sulfate headgroup. Pyrene fluorescence indicates formation of excimers whose intensity increases with concentration of solubilized pyrene indicating that they are mobile. Pyrene solubilized in the anchored bilayer exhibits unusual phenomena; on evacuation the excimer band disappear but reappears on releasing vacuum. It is shown that this behavior arises due to the loss of water of hydration of the headgroup on evacuation and as a consequence the pyrene moves into the less polar interior of the bilayer where it is immobile and can no longer diffuse and form excimers. The motion of pyrene into the interior of the bilayer creates free space near the surfactant chain termini, which manifests in the disappearance of the methyl-rocking mode of the ordered (-tt) end-chain conformer in the Raman spectra.

Synthesis and Aqueous Colloidal Solutions of RE2(OH)5NO3·nH2O (RE = Nd and La)

“…[12,17] The broad and sharp absorptions at 1182-982 and 1247 cm -1 in Figure 5e correspond to the S-O symmetric and asymmetric stretching vibrations of the sulfate group in La 2 (OH) 5 (decyl sulfate)·H 2 O, respectively. [5,[18][19][20] Such observations of characteristic bands for carboxylate, sulfonate, and sulfate groups confirm the intercalation of the corresponding organic anions into the interlayer space of LNdH and LLaH.…”

Electronic structure of the benzene dimer cation

“…Electronic excitation, especially to diffuse Rydberg orbitals, may have a similar effect, and rare gas or aromatic excimers are well known examples. [21][22][23][24][25] In the benzene dimer, additional complexity arises due to high symme-try of the monomer, which results in degenerate states of C 6 H 6 + that undergo Jahn-Teller ͑JT͒ distortions. [26][27][28] Both intramolecular and intermolecular degrees of freedom may be involved.…”

Luminous relative humidity sensing by anionic fluorescein dyes incorporated into layered double hydroxide/1-butanesulfonate hybrid materials

“…Constantino et al [1] have reported that photoluminescence (PL) properties of methyl orange incorporated into the LDH interlayer space were changed by water adsorption accompanied by hybrid material swelling. Mohanambe et al [2] showed that PL properties of LDH/dodecylsulfate hybridized with pyrene were changed with varying RH of a particular environment. Shi et al [3][4][5] studied PL of solid materials containing anionic fluorescein dyes (AFD) and surfactant anions hybridized with LDH, which could be potentially used as optical sensors for soluble organic compounds or pH indicators.…”