Influence of Aggregation on the Structure and Fluorescent Properties of a Tetraphenylethylene Derivative: a Theoretical Study.

The case that aggregation has a large influence on the structure and fluorescent properties of 5-(4-(1,2,2-triphenylvinyl)phenyl)thiophene-2-carbaldehyde (P TA) is investigated in detail herein by employing quantum mechanics and molecular mechanics. Besides the isolated molecule, the aggregated molecule in water and in the crystalline state was studied by focusing on the comparison of photoelectronic properties, including the geometrical and electronic structures at ground and excited states, emission and internal conversation properties. For the aggregation state, the intermolecular interaction was used to explain the difference in structure, emission color and intensity of different polymorphs. The noticeable contribution from low-frequency region, corresponding to the four phenyl rings twisting vibration, to the Huang-Rhys factor and reorganization energy, as well as the possible potential energy surface crossing between S and S states for isolated molecules was considered as the reason of its aggregation-induced emission (AIE) performance. Importantly, the aggregation process in water simulated at the same time helps us to have a deeper understanding of the AIE behavior of P TA, which also provides another perspective to explore the AIE phenomenon in theory.