Browsing by Author "Jankus, Vygintas"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Colour tuning from green to red by substituent effects in phosphorescent tris-cyclometalated iridium(III) complexes of carbazole-based ligands: Synthetic, photophysical, computational and high efficiency OLED studies
    (Royal Soc Chemistry, 2012) Moore, Tom N.; Zheng, Yonghao; Bryce, Martin R.; Fox, Mark A.; Griffiths, Gareth C.; Jankus, Vygintas; Al-Attar, Hameed A.; Monkman, Andrew P.; Tavaslı, Mustafa; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; 0000-0002-9466-1111; AAB-1630-2020; 6506308760
    Two series of fac-tris-cyclometalated iridium(III) complexes, series 1 from the 2-(carbazol-3'-yl)-pyridine ligands, and series 2 from the isomeric 2-(carbazol-2'-yl)-pyridine ligands, have been characterised. The photoluminescence and electroluminescence from series 2 complexes are red shifted compared to series 1 complexes, due to the increased electron donating ability of the carbazole unit in series 2. The attachment of trifluoromethyl and methoxy substituents to the pyridyl ring in these complexes results in colour tuning of phosphorescence energy maxima over the range 494-637 nm (green to red). These complexes possess predominantly (MLCT)-M-3 (metal-to-ligand-charge transfer) excited states. DFT/TD-DFT computations correctly predict the phosphorescence emission maxima and show that the HOMOs in these complexes contain mixed iridium and carbazolyl character. The carbazolyl ligand contributions to the excited states increase in series 2 compared to series 1. Complexes of series 1 exhibit high phosphorescence quantum yields whereas complexes of series 2 show lower quantum yields. Solution processed organic light emitting devices (OLEDs) with series 1 complexes using the high triplet poly(9-vinylcarbazole) (PVK) as the host polymer exhibit very high performances of up to 40 cd A(-1) and external quantum efficiency of 12%. For series 2 the highest current efficiency is 10.3 cd A(-1) and external quantum efficiency of 5.6%.
  • No Thumbnail Available
    Item
    High efficiency OLEDs based on anthracene derivatives: The impact of electron donating and withdrawing group on the performance of OLED
    (Elsevier, 2016-03) Aydemir, Murat; Haykır, Gülçin; Battal, Ahmet; Jankus, Vygintas; Sugunan, Sunish K.; Dias, Fernando B.; Al-Attar, Hameed; Türksoy, Figen; Monkman, Andrew P.; Tavaslı, Mustafa; Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Kimya Bölümü.; 0000-0002-9466-1111; AAB-1630-2020; 6506308760
    New well-defined bulky anthracene derivatives with side groups having electron donating or withdrawing properties 8a-d were synthesized. The compounds contain substituted anthracene as the central core attaching 2-(4-(2-pyridinyl)-phenyl)vinyl and 4-R-phenyl [R:H (a), OMe (b) and CF3 (c), N(Ph)(2) (d)] groups at 9- and 10-positions. The impact of electron donating, withdrawing and neutral groups and their influence on the molecules photophysical, charge transfer (CT), triplet transfer (TT) and triplet-triplet annihilation (TTA) properties has been investigated. Based on the photophysical studies the most promising molecule (8d) has been selected and high efficiency fluorescent OLEDs with EQE at very low current efficiency reaching 7% were obtained. The value at low current density implies a Triplet Fusion (TF) contribution of 45%, very close to the maximum theoretical value of 50% when only the singlet decay channel is open to TTA, however we believe that in this case both TTA and TADF contribute to the triplet harvesting to yield high EQE values, and this mixed triplet harvesting arises through the heterogeneity of the films. At high current density a brightness of 20000 cd/m(2) was achieved and it is assigned partially to the material crystallisation.