DESIGN OF A TWISTED DOUBLE DONOR IN CARBAZOLE-METHYLPYRIMIDINE-BASED EMITTERS LEADING TO THE TRIPLE CHARGE-TRANSFER EMISSION

Dovydas Blaževičius; Gintarė Kručaitė; Saulius Grigalevičius; Oleg Dimitriev

Open Readings 2025 • P1-42

DESIGN OF A TWISTED DOUBLE DONOR IN CARBAZOLE-METHYLPYRIMIDINE-BASED EMITTERS LEADING TO THE TRIPLE CHARGE-TRANSFER EMISSION

Dovydas Blaževičius¹, Gintarė Kručaitė¹, Saulius Grigalevičius¹, Oleg Dimitriev²

¹ Department of Polymer Chemistry and Technology, Faculty of Chemical Technology, Kaunas University of Technology, Lithuania

² V.E. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Ukraine

[email protected]

The advantages that organic light emitting diode (OLED) based technologies offer in terms of brightness, viewing angle, contrast ratio, production cost, etc. are not rivalled by liquid crystal-based displays. In this study we present novel methylpyrimidine-carbazole derivatives and influence of complication of donor arm structure to emissive properties. Thermally activated delayed fluorescence (TADF) is a now well-known emission mechanism which make it theoretically possible to achieve 100% internal quantum efficiency.Novel D2-D1-A-D1-D2 emitters with the donor arm composed of a double twisted donor-donor moieties provide additional routes for charge-transfer (CT) emission. Here we show that a structural complication of the donor arm by additional donor moiety, i.e., from D-A-D to D2-D1-A-D1-D2 yields a transition from a dual to triple CT band with corresponding red shift and increasing contribution of the low-energy emission components. The observed relationship between complexity of the donor moiety and multicomponent CT emission band in various D-A-D structures provides a clue for design of thermally activated delayed fluorescence emitters with controllable emission properties. Figure 1 depicts photoluminescence spectra, chemical structures and HOMO-LUMO distribution of new compounds.

**Fig. 1.** PL emission spectra (green - chloroform, brown – THF, black - acetone solutions, all 10-5 M), chemical structures, HOMO and LUMO distribution

Comparison of PL emission spectra of 1, 2, and 3 in the same solvent further elucidates the difference related to the dye complexity. Specifically, in chloroform, the relative contribution of the LE emission component in terms of the integral of the first Gaussian in the spectra of 1, 2, and 3 constitutes 51:2:0, respectively, whereas the relative contribution ratio of CT1 component is 21:82:62, respectively. For CT2, the ratio is 0:18:60, respectively. That is, the compound 1 does not possess the CT2 emission, while the compound 3 losses the LE emission, respectively. In conclusion, complication of the donor arm in the twisted D-A-D compounds leads to increasing twisting disorder and, as a consequence, to appearance of additional charge-transfer routes from the different donor moieties. This is displayed as appearance of additional emission components and broadening of the PL emission spectra. The observed relationship between complexity of the donor moiety and multicomponent CT emission band in the D-A-D structures suggests new design principles of thermally activated delayed fluorescence emitters with controllable emission properties. This work was financially supported by the Research Council of Lithuania (Grant No. S-LU-24-7) and Ministry of Education and Science of Ukraine (project М/54-2024) and in part by the Knut and Alice Wallenberg Foundation (KAW) through the Wallenberg Wood Science Center.