Helios, as a character of the sun in Greek mythology, represents human’s pursuit of light. From the fifth century B.C., humans began investigating and utilizing natural light sources. With the rapid development of science and technology during the past decades, luminescent materials are fabricated and have been widely used in our daily life, including illumination, displaying, communication, biology, and medicine. However, many traditional luminogens based on through-bond conjugation show aggregation-caused quenching (ACQ) that their emissions are quenched in the aggregate state. The emergence of aggregation-induced emission (AIE) in 2001 promoted a new era for luminescent materials. Luminogens with AIE effect (AIEgens) are nonemissive in the solution but highly emissive in the aggregat...[ Read more ]

Helios, as a character of the sun in Greek mythology, represents human’s pursuit of light. From the fifth century B.C., humans began investigating and utilizing natural light sources. With the rapid development of science and technology during the past decades, luminescent materials are fabricated and have been widely used in our daily life, including illumination, displaying, communication, biology, and medicine. However, many traditional luminogens based on through-bond conjugation show aggregation-caused quenching (ACQ) that their emissions are quenched in the aggregate state. The emergence of aggregation-induced emission (AIE) in 2001 promoted a new era for luminescent materials. Luminogens with AIE effect (AIEgens) are nonemissive in the solution but highly emissive in the aggregate state, which is opposite to the ACQ effect. The development of AIE not only provides a platform for luminescent materials but also bridges the microscopic molecules with macroscopic materials. Accordingly, some new phenomena and photophysical properties are also discovered, and the mechanisms behind these processes are attractive to be explored. In the dissertation, several mechanistic works focusing on through-space interactions and the dynamic behaviors of AIE materials are carried out.

Through-space interaction (TSI) is proved as the general mechanism for newly emerged clusteroluminescence that nonconjugated luminogens can brightly emit visible light in the aggregate state. However, it is still challenging to manipulate the photophysical behaviors and strength of TSI. Here, several nonconjugated triphenylmethane derivatives are developed to investigate the electronic effect on TSI. It reveals that the introduction of electron-donating groups could red-shift the wavelength and increase the efficiency of clusteroluminescence simultaneously, benefitting from the increased electronic density and stabilization of excitedstate geometry. In addition, three flexible and non-conjugated molecules based on triphenylmethane are synthesized to realize multiple emissions and even single-molecule whitelight emission. The concept of secondary TSI is innovatively proposed, and its role for clusteroluminogens with isolated D−A structure is also emphasized.

The AIE effect is closely related to intermolecular interactions and molecular motions, so AIE materials usually display dynamic behaviors under external stimuli. Nevertheless, the motion-structure-property relationship of AIE materials is unclear, and molecular skeletons with both AIE and dynamic properties are scarce. In this part, several AIEgens with a rotor are first designed and synthesized to decipher the dependence of materials’ structures and properties on molecular motions at single molecule, aggregate, and macro-crystal levels. It also provides a strategy to construct AIE crystals with elastic performance. Besides, a series of dihydroazulene-based compounds are developed, which show both AIE effects and photofluorochromic properties controlled by light. Accordingly, a rewritable four-dimensional information encryption system is designed and demonstrated with multiple characteristics.

At last, inspired by the restriction of the intramolecular vibration (RIV) mechanism, two 8-electron conjugated and nonaromatic quinolizine derivatives are developed. Their strong V-shape vibrations realize the visualization of molecular motions and endow them with AIE and ROS production properties in the aggregate state, showing potential applications in imagingguided photodynamic therapy.

These works are expected to provide a more comprehensive picture of the mechanisms of AIE materials, especially for the through-space interactions of clusteroluminescence and dynamic behaviors at both single-molecule and aggregate levels.