Organic fluorescent materials with aggregation induced emission (AIE) property are very popular and have lots of applications in various fields. In this thesis, the first project is investigating the photo physical properties of a novel AIE system, Tetraphenylpyrazine (TPP) and its two derivatives, TPP-2P and TPP-2PM, both in gas and solid phases computationally by employing the correlation function rate formalism coupled with combined quantum mechanical and molecular mechanical (QM/MM) simulations to figure out the mechanism. We have found that the pyrazine group is not planar. And besides the rotation of the phenyl group, the motions of the pyrazine group play a critical role to decay the excitation energy non-radiatively to quench the fluorescence in isolated state. In cluster, the l...[ Read more ]

Organic fluorescent materials with aggregation induced emission (AIE) property are very popular and have lots of applications in various fields. In this thesis, the first project is investigating the photo physical properties of a novel AIE system, Tetraphenylpyrazine (TPP) and its two derivatives, TPP-2P and TPP-2PM, both in gas and solid phases computationally by employing the correlation function rate formalism coupled with combined quantum mechanical and molecular mechanical (QM/MM) simulations to figure out the mechanism. We have found that the pyrazine group is not planar. And besides the rotation of the phenyl group, the motions of the pyrazine group play a critical role to decay the excitation energy non-radiatively to quench the fluorescence in isolated state. In cluster, the low-frequency modes have been restricted, which contributes to the decrease of the non-radiative rate constant by about 2~3 orders of magnitude. As a consequence, the luminescence quantum efficiency in aggregates increases. The influence of modifying more phenyl groups has been studied carefully.

Besides the theoretical study of the AIE mechanism, we further synthesized a series of 2,5-bis(4-methoxyphenyl)-1-methyl-1,3,4-triphenyl-silole with different length of alkyl chain to study the alkyl chain effect on the AIE effect and hydrophobic interactions. The structures and optical properties were studied. The experimental results illustrated that the length of the alkyl chain does not introduce a significant impact on AIE optical properties such as absorption spectrum, emission spectrum and fluorescence quantum yield. However, we found that the length of alkyl chain has substantial impact on the solubility measurements of amorphous aggregates brought together by hydrophobic interactions. Hence, these AIE systems could be suitable for the study of the thermodynamics and kinetics of hydrophobicity aggregations in the future. The effect of the length of alkyl chain on the strength of hydrophobic interactions, cooperativity and aggregation kinetics would be studied quantitatively.