title: Structural and theoretical insights into the AIE attributes of phosphindole oxide: the balance between rigidity and flexibility.
abstract: Multiple intramolecular motions consume the excited-state energy of luminogenic molecules upon photoexcitation and lower the emission efficiency. The low frequency rotational motion of aromatic rings can be facilely restricted by steric constraint in the condensed phase, but the high frequency bond stretching motion can hardly be suppressed by aggregation. In this work, three phosphorus-containing heterocycles, 1,2,3,4,5-pentaphenylphosphole-1-oxide (PPPO), 1,2,3-triphenylphosphindole-1-oxide (TPPIO), and 1,2,3-triphenylphosphindole (TPPI), were synthesized and characterized. Their optical properties, crystal-packing manners, electronic features, and fluorescence dynamics were systematically investigated, and theoretical calculations were performed to decipher structure-property relationships. The results reveal that these luminogens are weak emitters in solutions but show strong emission in aggregates, exhibiting obvious aggregation-induced emission (AIE) features. The aggregation-insensitive stretching motion, which is dominant in PPPO, is lowered in TPPIO, enabling TPPIO to fluoresce much more efficiently than PPPO in aggregates. The stretching motion is even more lowered in TPPI, but its relatively planar conformation suffers emission quenching due to strong π-π stacking interactions in aggregates. Therefore, a twisted molecular conformation consisting of a rigid stator and a rotatable periphery is demonstrated to be a rational design for more efficient AIE luminogens.
authors: Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology (SCUT), Guangzhou 510640 (P.R. China).
authors: Fan
authors: F
authors: Bu
authors: Erjing
authors: E
authors: Wang
authors: Qian
authors: Q
authors: Peng
authors: Rongrong
authors: R
authors: Hu
authors: Anjun
authors: A
authors: Qin
authors: Zujin
authors: Z
authors: Zhao
authors: Ben Zhong
authors: BZ
authors: Tang
mesh_terms: D005453:Fluorescence; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D010087:Oxides
keywords: aggregation; intramolecular motion; phosphindole oxides; photoluminescence; theoretical calculation