講演情報
[14p-K508-8]Rational molecular design strategy to obtain locally excited and charge transfer characters aimed for dual enhancement of two-photon absorption cross-section and TADF activity
〇(D)GomathiVinayakam Mageswari1, Youhei Chitose1, Ja-Hon Lin2, Youichi Tsuchiya1, Chihaya Adachi1 (1.Kyushu Univ, 2.Nati Taipei Univ Tec)
キーワード：
organic light emitting diiodes、TADF、two photon absorption
The pursuit of an effective molecular design for highly efficient thermally activated delayed fluorescence (TADF) emitters with two-photon absorption (2PA) character is hampered by the concurrent achievement of a small singlet-triplet energy gap and a large oscillator strength with hybridized LE and CT characters. Here, by introducing a terephthalonitrile unit into a sterically crowded D-π-D structure, we designed TADF emitters with 2PA phenomenon by bearing hybrid electronic excitation character. This rational molecular design was achieved through a main π-conjugated donor-acceptor-donor (π-DAD) in line with locally excited features and an auxiliary N-donor-acceptor-donor (N-DAD) with charge transfer (CT) character, highly balancing the TADF phenomenon by a small and maintaining high 2PA cross-section with a large. Moreover, the incorporation of naphthyl groups was found to manipulate the emission properties without surrendering the photoluminescence quantum yield (PLQY). A near-unity PLQY value with a large radiative decay rate over an order of magnitude higher than the intersystem crossing (ISC) rate and a high horizontal orientation ratio of 0.95 were simultaneously obtained for the emitter of TPCz2NP. By overcoming the trade-off of molecular design between TADF and 2PA materials with a rigid molecular framework, an optimal goal of efficient OLED and moderate 2PA ability was successfully achieved. The organic light-emitting diode (OLED) fabricated with this material exhibits a record-high maximum external quantum efficiency (EQE) of 25.4%. Further, we confirmed that the hybridized molecule with balanced LE and CT characters also gave rise to an enhancement of the 2PA cross-section up to 143 GM at 850 nm, which is the highest value among the reported TPN-based TADF emitters with EQE values exceeding 25%. These findings offer a venue for designing high-performance TADF emitters with exceptional 2PA properties, expanding future OLED material design.