Polymorphous Luminescent Materials Based on ′T′‐Shaped Molecules Bearing 4,7‐Diphenylbenzothiadiazole Skeletons: Effect of Substituents on the Photophysical Properties

• Published in: Chemistry : a European journal Vol. 25; no. 67; pp. 15401 - 15410
• Main Authors: Qian, Gaowei, Wang, Xiangbing, Wang, Shengyue, Zheng, Yanqiong, Wang, Song, Zhu, Weiguo, Wang, Yafei
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.12.2019
• Subjects: Calorimetry; Chemical compounds; Chemistry; Differential scanning calorimetry; Diodes; Fluorescence; Light microscopy; Luminescence; Mechanoluminescence; Optical microscopy; Optical properties; Organic chemistry; Organic light emitting diodes; Photoluminescence; Polymorphism; Quantum efficiency; Stability analysis; Thermal stability; Thermogravimetric analysis
• DOI: 10.1002/chem.201904026
• ISSN: 0947-6539

Polymorphism, the intrinsic character of one chemical compound with at least two distinct phase arrangements, plays a very key role in the photophysical properties. In this contribution, four ′T′‐shaped molecules bearing the 2,1,3‐benzothiadiazole (BTD) skeleton, named 5 a–5 d, were prepared and characterized. All compounds exhibited excellent thermal stability and polymorphism in the solid state, evident from thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy results. Intense emissions with high photoluminescent quantum yields were achieved both in solution (56–97 %) and neat films (33–98 %). All compounds possessed clearly pH‐dependent luminescence properties in solution. Additionally, compound 5 d showed useful mechanochromic luminescence owing to the transformation between the crystal and amorphous state. Employing compounds 5 a–5 d as the dopant, solution‐processable organic light‐emitting diodes (OLEDs) were fabricated and presented a highest external quantum efficiency of 6.15 %, which is higher than the theoretical value of fluorescence‐based OLEDs (∼5 %). This research provided a novel strategy for designing high‐efficiency BTD‐based polymorphic luminescent materials.