Facile structure-modification of xanthenone based OLED emitters exhibiting both aggregation induced emission enhancement and thermally activated delayed fluorescence

• Published in: Journal of luminescence Vol. 220; p. 116955
• Main Authors: Nasiri, Sohrab, Macionis, Simas, Gudeika, Dalius, Volyniuk, Dmytro, Grazulevicius, Juozas V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2020
• Subjects: Aggregation induced emission enhancement; Organic light-emitting diode; Thermally activated delayed fluorescence; Xanthenone; Thermally activated delayed fluorescence; Xanthenone; Organic light-emitting diode; Aggregation induced emission enhancement
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2019.116955

Four new donor-acceptor compounds were designed, synthesized and investigated by theoretical and experimental approaches aiming to estimate effect of the structure of a donor on the properties of potential OLED emitters. Because of the different electron-donating abilities of the nitrogen-containing heterocycles, derivatives of xanthenone containing di-tert-butyl-carbazolyl, di-tert-butyl-acridanyl, di-tert-butyl-phenothiazinyl and penoxazinyl moieties exhibited different photophysical behavior. Because of big dihedral angles between the donors and acceptor as well as because of possibility of rotation around N–C bond, the designed compounds were characterized by thermally activated delayed fluorescence and aggregation induced emission enhancement effect. Twice higher photoluminesce quantum yields reaching 38% in doped films were obtained for compounds containing di-tert-butyl-carbazolyl and di-tert-butyl-acridanyl moieties as compared to those observed for compounds with the donors containing S and O heteroatoms. Strong effect of the donor substituents on charge injection (ionization potentials were in the range of 5.67–5.96 eV) and charge-transporting properties (hole and electron mobilities were in a wide range from 6.3 × 10−8 to 6.3 × 10−4 cm2V−1s−1 at electric field of 2.5 × 105 V cm−1) was detected. The differently substituted compounds were utilized as emitters in OLEDs. Higher maximum values of external quantum efficiency (up to 3.5%) were observed for OLEDs based on emitters with nitrogen containing donors relative to estimated for OLEDs based on emitters containing di-tert-butyl-phenothiazinyl and penoxazinyl moieties. [Display omitted] •Xanthenone-based OLED emitters were designed and synthesized.•Their glass transition temperatures ranged from 70 to 116 °C.•Their ionization potentials were in range of 5.70–5.95 eV.•Hole and electron mobilities reached 10−8 and 10−4 cm2/V·s, respectively at electric field of 2.5 × 105 V cm−1.•2-(2,7-Di-tert-butyl-9,9-dimethylacridin-10(9H)-yl)-9H-xanthen-9-one showed maximum external quantum efficiencies of 3.5%.