title: A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes.
abstract: Two benzoylpyridine-carbazole based fluorescence materials DCBPy and DTCBPy, bearing two carbazolyl and 4-(t-butyl)carbazolyl groups, respectively, at the meta and ortho carbons of the benzoyl ring, were synthesized. These molecules show very small ΔEST of 0.03 and 0.04 eV and transient PL characteristics indicating that they are thermally activated delayed fluorescence (TADF) materials. In addition, they show extremely different photoluminescent quantum yields in solution and in the solid state: in cyclohexane the value are 14 and 36%, but in the thin films, the value increase to 88.0 and 91.4%, respectively. The OLEDs using DCBPy and DTCBPy as dopants emit blue and green light with EQEs of 24.0 and 27.2%, respectively, and with low efficiency roll-off at practical brightness level. The crystal structure of DTCBPy reveals a substantial interaction between the ortho donor (carbazolyl) and acceptor (4-pyridylcarbonyl) unit. This interaction between donor and acceptor substituents likely play a key role to achieve very small ΔEST with high photoluminescence quantum yield.
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Pachaiyappan
authors.initials: P
authors.lastname: Rajamalli
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Natarajan
authors.initials: N
authors.lastname: Senthilkumar
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Parthasarathy
authors.initials: P
authors.lastname: Gandeepan
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Pei-Yun
authors.initials: PY
authors.lastname: Huang
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Min-Jie
authors.initials: MJ
authors.lastname: Huang
authors.affiliation: Department of Materials Science and Engineering, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Chen-Zheng
authors.initials: CZ
authors.lastname: Ren-Wu
authors.affiliation: Department of Materials Science and Engineering, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Chi-Yu
authors.initials: CY
authors.lastname: Yang
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Ming-Jui
authors.initials: MJ
authors.lastname: Chiu
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Li-Kang
authors.initials: LK
authors.lastname: Chu
authors.affiliation: Department of Materials Science and Engineering, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Hao-Wu
authors.initials: HW
authors.lastname: Lin
authors.affiliation: Department of Chemistry, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Chien-Hong
authors.initials: CH
authors.lastname: Cheng