Mechanochromic luminescent derivatives based on xanthenone and thioxanthenone for the fabrication of OLED devices as emitter layer

New compounds consisting of xanthenone and thioxanthenone derivatives are synthesized and the photophysical properties of the compounds are discussed in detail. The difference between singlet and triplet energies was obtained at 0.09 and 0.37 eV (at low temperature). Furthermore, the logarithm of the laser power versus the logarithm of the PL intensity showed a slope of less than 1, and the compounds exhibit thermally activated delayed fluorescence (TADF). In addition, the photoluminescence quantum yield of the spin-coated films was gained 51.83 and 41.22%, respectively. The powder X-ray diffraction of the grinded (under the force) compounds and also the PL spectrum of the compounds were shifted and the compounds were mechanochromic when the color of the compounds was changed. The ionization potential of the compounds showed (5.49 and 5.62 eV) that the compounds were well suited for using in the fabrication of OLED devices as an emitter layer. The performance of the OLEDs was investigated and the maximum brightness and external quantum efficiency were found to be 44573 cdm-2 and 12.61%, respectively.