Structure and Host–Guest Interactions of Perylene–Diimide Dyes in Zeolite L Nanochannels

Abstract

Confinement-driven self-assembly of dyes in nanomatrices is an effective route for the production of hybrid supramolecular structures of high technological relevance, among which the archetypal zeolite L based systems are exploited in Forster resonance energy transfer (FRET) sensitized solar cells, luminescent solar concentrators, and color-changing media but also in sensing in analytical chemistry, biology, and diagnostics. Despite this progress in applications, the organization of confined chromophores in zeolite L materials remains elusive. Herein, by integrating experiments with different time scale and radiation source (IR, XRPD, total scattering) with first-principles DFT modeling, we attained a microscopically detailed picture of a technologically important hybrid composite of zeolite L with a perylene−diimide (also known as perylene−bisimide) dye at both hydrated and anhydrous conditions. The asymmetric positioning of the dye in the zeolite channel is determined by two factors: shapevolume constraints, and relative strength of competitive interactions among confined species. Our multitechnique experimental-theoretical approach thoroughly described the supramolecular chemistry of this hybrid material, identifiying possible strategies to further enhance FRET efficiency and improve functionality. This work deepens the understanding of host−guest interactions in dye−zeolite L composites, a key requirement to master the finely tuned mechanisms governing supramolecular organization in confined nanospaces.

Supramolecular Organization in Confined Nanospaces

“…Though the composites are technically suitable for use in solar cells and sensing applications (Section 7), acidity inside the zeolite L channel is still a limiting factor towards attaining maximum concentration of donor molecules inside the host . Nevertheless, these composites have proven to be thermally robust, and mechanically resilient up to GPa pressures; in addition, the host matrix is easy to synthesize in form of disc‐shaped crystals, for which a uniform filling of dye molecules along the channels can be accomplished . Also, the use of nanosized zeolite L crystals could further improve the luminescence properties of these hybrid materials, disclosing potential medical applications as theranostic agents …”

“…Also the dye carbonyl groups are crucial, as shown by a recent study . Indeed, X‐ray diffraction, total scattering, IR and UV‐vis data combined with modeling revealed that the perylene dye tb‐DXP is asymmetrically positioned in the channels in order to optimize, compatibly with the steric constraints, the stabilizing interactions between its carbonyl groups and the zeolite potassium cations . The relevance of the C=O⋅⋅⋅ K + interaction (amounting to ∼26 kcal/mol for perylene‐diimide) can be better understood by considering a carbonyl dye of smaller size: fluorenone.…”

“…Nonetheless, the atomistic structure of these versatile compounds often remains unexplored, as suggested by the scarce number of diffraction studies on dye‐zeolite hybrids ,. Fortunately, computational modeling comes to the rescue .…”

“…In this case, the organization is dictated by the space constraints of the matrix, but it is fine‐tuned by the geometry of the dye;, for example, the spacing between the photoactive perylene cores can be tuned via the choice of end‐substituents . Also the dye carbonyl groups are crucial, as shown by a recent study . Indeed, X‐ray diffraction, total scattering, IR and UV‐vis data combined with modeling revealed that the perylene dye tb‐DXP is asymmetrically positioned in the channels in order to optimize, compatibly with the steric constraints, the stabilizing interactions between its carbonyl groups and the zeolite potassium cations .…”

Unravelling the High-Pressure Behaviour of Dye-Zeolite L Hybrid Materials

“…The nanometric-scale geometry of zeolite pore systems allows the intensive use of zeolites in several fields such as in molecular separation processes and in heterogeneous catalysis [3,4]. Such ongoing progress in applications has been accompanied, in the latest years, by a deeper molecular-level understanding of the confined photoactive assemblies, which has been achieved through computational modelling [44][45][46][47][48][49][50], often combined with multi-technique experimental analyses [45,[50][51][52][53][54][55][56][57]. The key role of water in tuning the organization of the confined chromophores has been revealed [45,46,58], as well as the stabilizing effect of potassium cations in composites with carbonyl dyes [44,57,59].…”