Browsing by Author "Hizal, Gurkan"

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Effects of Asymmetric Acceptor and Donor Positioning in Deep Blue Pyridyl-Sulfonyl Based Tadf Emitters
(Elsevier Sci Ltd, 2021) Haykir, Gulcin; Aydemir, Murat; Danos, Andrew; Gumus, Selcuk; Hizal, Gurkan; Monkman, Andrew P.; Turksoy, Figen
In this work, we report synthesis and photophysical properties of deep-blue emitting donor-acceptor (D-A) and donor-acceptor-donor (D-A-D) thermally activated delayed fluorescence (TADF) molecules, where the molecules designed using carbazole as a donor (D) and a pyridyl (a)-sulfonyl (A) based bifunctional group as an acceptor. The work reveals how structural changes favor reverse intersystem crossing (rISC) by forming emissive charge transfer (CT) state, which is thoroughly investigated in different donor and asymmetric acceptor positions. Three comparison sets of regioisomers are investigated. 2,5-substituted pyridine derivatives in Set-1, are D-Aa, D-aA and D-Aa-D structures with asymmetric acceptor systems, revealing that the donor nearer to the pyridine group substantially controls the TADF properties In Set-2, modified the D-Aa-D structures reveal how ortho and meta positioned a relative to A (keeping the carbazole at meta to the A) affects the emission properties, deactivating TADF and promotion triplet-triplet annihilation. In the final set, 2,4-substituted pyridyl-sulfonyl derivatives show that the positioning of the donor far from the pyridine group has minimal influence. This final set of molecules show superior optical and physical properties though, indicating the importance of correct positioning between D, a, and A.
The Investigation of Sky-Blue Emitting Anthracene-Carbazole Derivatives: Synthesis, Photophysics and Oled Applications
(Elsevier, 2018) Haykir, Gulcin; Aydemir, Murat; Han, Si Hyun; Gumus, Selcuk; Hizal, Gurkan; Lee, Jun Yeob; Turksoy, Figen
New well-defined structurally different 9,10-bis(9-hexyl-6-((E)-styryl)-9H-carbazol-3-yl)anthracene derivatives, shortly named "6a, 6b and 6c", with side groups having electron donating and withdrawing were systematically synthesized using Suzuki cross-coupling and Vilsmeier-Haack reactions. The impact of electron donating and withdrawing groups and their influence on the molecules photophysical properties has been investigated. The materials showed sky-blue emissions with high internal quantum efficiencies. Based on photophysical investigations the most promising molecule (6a) has been selected and high efficiency OLEDs with external quantum efficiency at very low current efficiency (similar to 1 mA/cm(2)) reaching 5% (doped) were obtained.