Origin of Intense Luminescence from Supramolecular 2D Molecular Crystals

Abstract

Luminescence enhancement in 2D molecular crystals (2D crystals) is promising for a variety of optical applications, yet the availability is limited because of unclear mechanism and inefficient design strategy of luminescence control. Herein, the room temperature phosphorescence from micron long molecular thin free‐standing 2D crystals of a mono‐cyclometalated Ir(III) complex designed at the water surface is reported. A large luminescence enhancement is observed from the 2D crystals at 300 K, which is comparable with the rigidified solution at 77 K suggesting room temperature phosphorescence origin of the luminescence. In situ synchrotron grazing incidence X‐ray diffraction measurements determine the constituent centered rectangular unit cells with precise molecular conformation that promotes the formation of 2D crystals. The molecular crystal design leads to a reduced singlet‐triplet energy gap (ΔEST) and mixing of singlet‐triplet states by spin‐orbit coupling (SOC) for efficient intersystem crossing, which explains the phosphorescence origin at room temperature and luminescence enhancement. The supramolecular assembly process provides an elegant design strategy to realize room temperature phosphorescence from 2D crystals by rigid intermolecular interactions.

Origins of Molecular-Twist-Triggered Intersystem Crossing in Functional Perylenediimides: Singlet–Triplet Gap versus Spin–Orbit Coupling

“…Triplet exciton generation via intersystem crossing (ISC) is of great importance in phosphorescence, electroluminescence, photodynamic therapy, and photovoltaics. − Efficient ISC can be realized by large spin–orbit coupling (SOC) and an optimal singlet–triplet gap (Δ E S – T ). For thermally accessible small Δ E S – T , the ISC competes with the reverse ISC (RISC) in systems with low-lying triplets.…”

Opportunities and new developments for the study of surfaces and interfaces in soft condensed matter at the SIRIUS beamline of Synchrotron SOLEIL

“…Because of the significant interception of the beam with the liquid surface under grazing-incidence conditions (of the order of 50 mm  1 mm), the previous GIWAXS geometry yields poor angular resolution on liquid surfaces, making it unsuitable for obtaining valuable measurements. GIXD provided a major breakthrough in the understanding of Langmuir films in the 1990s (Kaganer et al, 1999) and has since been widely used to explore various systems, including the self-assembly of molecular rigid rods (Fontaine et al, 2019), the effects of drugs and pollutants on biomimetic systems (Michel et al, 2015;Pereira-Leite et al, 2019;Lopes-de-Campos et al, 2021;Wo ´jcik et al, 2022;Matyszewska et al, 2023), luminescence in 2D molecular crystals (Biswas et al, 2021) and the structure of graphene oxide films (Bonatout et al, 2017).…”

Front Cover: Exploiting Hydrogen Bonding to Direct Supramolecular Polymerization at the Air/Water Interface (ChemNanoMat 1/2023)

“…[8] While solid/liquid and liquid/liquid interfaces have been used for obtaining SPs at interfaces, whereas air/liquid interfaces remain a promising platform in this sense. [9][10][11][12] Hydrogen bonding interactions (H-bonding) are commonly used directional non-covalent forces for directing self-assembly processes, both in solution and in bulk conditions. [13][14][15] In addition, H-bonding at the air/water interface has been successfully applied to monolayers of surfactants with complex headgroups for sustaining the 2D crystalline structure.…”