To understand the nature of materials, scientists usually adopt the “Top-Down” approaches based on the reductionism conjecture to segment the macroscopic substance into the microscopic molecular species, in which the philosophical linkage is the epistemology that the molecule will retain properties of the substance. However, the research outcomes derived from the isolated molecular states may be invalid or even diametrically opposed when the molecules gather into the aggregate state, which can be exemplified by the Beer’s law and well-known aggregation-caused quenching (ACQ) effect. When microscopic molecules are mixed or assembled into the mesoscopic aggregate, there are plentiful rooms to explore their properties, such as the quantity, geometry, morphology and interactions. Investigat...[ Read more ]

To understand the nature of materials, scientists usually adopt the “Top-Down” approaches based on the reductionism conjecture to segment the macroscopic substance into the microscopic molecular species, in which the philosophical linkage is the epistemology that the molecule will retain properties of the substance. However, the research outcomes derived from the isolated molecular states may be invalid or even diametrically opposed when the molecules gather into the aggregate state, which can be exemplified by the Beer’s law and well-known aggregation-caused quenching (ACQ) effect. When microscopic molecules are mixed or assembled into the mesoscopic aggregate, there are plentiful rooms to explore their properties, such as the quantity, geometry, morphology and interactions. Investigation on the aggregate with higher levels of structural hierarchy and complexity will lead to novel discoveries and innovations in the advanced material research.

Traditional research on luminescent materials always explore planar and rigid molecules in the dilute solutions, in which the molecular motions and the non-covalent interactions will be ignored. There keeps grey areas between the molecular motions and nonradiative decay pathways as well as between the radiative decay and the non-covalent interactions until the booming development the research on aggregation-induced emission (AIE) at the aggregate level. In this thesis, we have conducted systematic mechanistic study on the molecular motions and non-covalent through-space interactions based on the organic luminescent aggregates.

We firstly designed an AIE luminescent model compound TAO-TP based on the mesoionic ring with unique charge separation to explore the effect of molecular motions on the nonradiative decay process. We found that the mesoionic ring of the TAO-TP promotes the excited-state low-frequency molecular motions, and lead to the conical intersection, which finally causes drastically enhanced nonradiative decay. Meanwhile, the bending motions of the mesoionic ring leads to the bended intramolecular charge transfer state and results in the superior red/NIR light emission property. After dissection of the molecular motions in the excited-state decay pathways, we next built another series of model compounds based on the crown ether and succeeded in manipulating the molecular motions to achieve the excellent room temperature phosphorescence performance. Through modification of the ring size of the crown ether derivatives and through the supramolecular complexation method, we induced the interand intramolecular hydrogen bonding and chelation interactions with different extent to control the molecular motions and finally tuned the exiton lifetime to 950 ms.

On the other hand, the quantum origin of the through-space interactions (TSI) and its electronic effect still remain misty. Thus, we took the TPE as model compound to explore the power of TSI in the photophysical processes. We found that the stabilized excited-state through-space interactions between vicinal or geminal phenyl rings by the restriction of intramolecular motions will generate expanded through-space electron delocalization and promotes the visible light emission in the solid state of TPE. Furthermore, we employed the benzene, as a fundamental aromatic ring, to build an efficient solid-state luminescent system with total light efficiency of 45.9 %. By in-situ generation of radial species, we created the remote lighten-up optical switch system. With applying the hydrostatic pressure, we successfully manipulated the through-space interactions and achieved strong visible luminescence in the crystals, which provides a novel strategy to develop the efficient solid-state organic luminescent materials with three-dimensional electronic conjugation.