A pyrene-based platform for studying the relationship of steric effects on optical properties

Triphenylamine (TPA) is a weak fluorophore with an aggregation-caused quenching (ACQ) effect. By integrating pyrene and different substituents (such as benzene, pyrene, phenylcarbazole, tetraphenylethylene (TPE)), a set of new pyrene-based TPA analogues have been prepared in order to understand the stereoscopic effects on the emission behavior both in solution and in the solid state. These compounds contain the pyrene unit (such Py2Ph, 2PyPh and PyCz) can improve the fluorescence intensity but still exhibit an ACQ feature, while the TPE decorated compound PyTPE exhibited a typical aggregation-induced emission (AIE) characteristic. Moreover, the degree of π-conjugation and the electronic effects can affect the molar absorbance coefficients. Due to the stereoscopic effect of these TPA analogues, the emission compounds show slight changes before and after grinding. Furthermore, due to their good thermal stability and quantum yields, the compounds PyCz and PyTPE were selected as light emitting layers for fabricating organic light emitting diodes (OLEDs) which exhibited good electroluminescence properties.