Significant Influence of Molecular Packing in Aggregates on Optoelectronic Properties

Abstract

Organic materials based on small molecules are aggregates that composed of many molecules. Their properties are not only determined by the spatial configuration and electronic properties of individual molecule, but also closely related to the molecular packing modes and the intermolecular interactions in the aggregates. In the realm of organic molecules, the macroscopic performance of molecular aggregates is not just the simple superposition of single molecules, but often display overall differential response of aggregates, namely, distinct properties can be created by molecular uniting with particular packing modes. Therefore, molecular aggregation science has gradually appeared in scientific research and drawn much attention in recent years. With the continuous and serious exploration of molecular aggregation science, especially the in-depth study of the molecular packing modes and intermolecular interactions of organic molecules in the solid state, it is found that the luminescence based on aggregation state is completely different from the characteristics of individual molecule, including the emission intensity and color, emission type, and even the excitation process, which could be realized by regulating molecular aggregation behavior. In addition, the morphology and dimensions of the aggregates can also be adjusted to achieve excellent performances of optoelectronic devices. This review will introduce the important influence of the arrangement of aggregated molecules on mechanochromism, room temperature phosphorescence, mechanoluminescence and organic field effect transistors, and further elaborate the importance of the molecular packing, providing some guidance for regulating molecular packing mode and targeted design and development of high-performance optoelectronic materials.

Persistent room temperature phosphorescence films based on star-shaped organic emitters

“…9–11 Unlike most phosphors based on organometallic complexes containing noble metals, metal-free phosphors are rare due to the slow intersystem crossing (ISC) process and serious non-radiative relaxation of triplet excitons under ambient conditions (in air and at room temperature). 12,13 Therefore, various strategies to achieve persistent RTP materials have been developed to promote the ISC process by introduction of heavy atoms (Br, I), 14–17 heteroatoms (N, O, S, P, and so on) 18 or aromatic carbonyl groups, 3,19–23 and to suppress the non-radiative decay process by crystallization engineering, 5,22,24–28 embedding into rigid polymer matrix 3,8,29–31 and formation of supramolecular host–guest complexes. 32–35 Recently, significant progress has been made in crystal-based metal-free ultralong phosphors.…”

Advances in Pure Organic Mechanoluminescence Materials

“…Thus, ML is a special photophysical characteristic of an organic crystal, and the investigation from molecular arrangement would provide a new perspective for the emission mechanism of ML. Recently, an increasing number of studies indicate that the photophysical properties of organic luminophores in the solid state are tightly associated with molecular packing mode, spatial conformation, and intermolecular interactions. − Accordingly, in 2018, our group proposed the concept of “molecular uniting set identified characteristic” (MUSIC) to unveil the relationship between the unique stacking features and resultant optoelectronic properties at the molecular level. − Actually, the concept of MUSIC is just like symphony music: the basic atoms are like notes, and the molecules consisting of atoms with specific sequences are melodies constituted with the notes. The crystal formed by the aggregation of molecules in a particular packing mode is exactly a symphony made up of various melodies.…”

The influence of π–π stacking on the room temperature phosphorescence of phenothiazine 5,5-dioxide derivatives

“…The two polymorphisms of PTZO-Cl with totally different RTP effects could further certify this point, further demonstrating the Molecular Uniting Set Identified Characteristic (MUSIC). [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] In addition, a series of anti-counterfeiting applications were demonstrated, based on their distinct RTP effects. This study provides an effective strategy for regulating and controlling the intermolecular interactions of p systems, giving some new insights into the structure-packing-performance relationship of functional materials.…”