Precise Regulation of Distance between Associated Pyrene Units and Control of Emission Energy and Kinetics in Solid State

Abstract

Many approaches have been explored to tune emission behaviors of organic luminogens. However, precise regulation of distances in dimers is seldom reported. Here, four pyrene derivatives are presented, and we precisely regulate the distance between pyrene units of X2P. Its crystal manifests unusual deep-blue excimer emission at 424 nm, while the crystal of X1P with only one pyrene unit for each molecule gives sky-blue emission with a maximum emission peak at 475 nm, which even shows an unexpected bathochromic shift effect compared with the emission of the needle crystal of X2EP with the largest conjugated structure and tunable tristate kinetics of excimer emissions upon different stimuli. Notably, the excimer decay time of the X2P crystal (26.4 ns) is apparently shorter than that of the X1P crystal (106.0 ns). The qualitative and quantitative analysis of π-π interactions with different distances between pyrene units in crystals was performed for the first time, leading to the conclusion that short distance and strong π-π interactions are vital to lower excited-state energy and weaken delayed fluorescence. This study introduces an easy and efficient way to precisely regulate distances in dimer and control the emission energy and kinetics of the decay process in the solid state for unique applications, as well as to predict the distance based on emission wavelength.

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.…”

An Efficient Approach to Pyrene‐based Aggregation‐induced Emission Luminogens

“…To gain a deeper understanding of the molecular geometries and electronic structure of these pyrene‐based AIEgens, density functional theory (DFT) was performed using Gaussian 09 W at the B3LYP/ 6–311G(d,p) level. As shown in Figure 1, when the benzophenone unit(s) was connected to the pyrene core at the 1‐, 2‐ or 2,7‐positions by an oxygen atom as a bridge in compounds 1–3 , where one of phenyl ring of benzophenone is almost perpendicular to the pyrene ring with dihedral angle in range from 76–81°, the steric conformation is beneficial to adjust the distance of the π‐π stacking interaction [28] . The HOMO and LUMO levels of compounds 1–3 are mainly distributed on the pyrene ring.…”

Ultralong blue room-temperature phosphorescence by cycloalkyl engineering

“…Moreover, cycloalkyl moieties with varied shape can adjust the molecular packing by the different steric effect and intermolecular interactions, resulting in colortuneable RTP with green to blue emission and further confirming the concept of Molecular Uniting Set Identified Characteristic (MUSIC). [56][57][58][59][60][61][62][63][64][65][66] Among them, an ultralong blue RTP effect with lifetime up to 1116.10 ms has been achieved by the C 6 -CsO crystal, which is mainly due to the moderate electronic coupling, compact molecular packing and strong intermolecular interactions by crystal analysis and DFT calculation. This can be considered as an efficient strategy to realize persistent blue RTP emission, promoting applications in anti-counterfeiting and displays.…”