De Novo Design of Excited-State Intramolecular Proton Transfer Emitters via a Thermally Activated Delayed Fluorescence Channel

Developing
excited-state intramolecular proton transfer (ESIPT)
emitters with high photoluminescence quantum yields (ΦPLs) and long fluorescence lifetimes in solid state remains a formidable
challenge. In this study, we integrated the molecular design tactics
of thermally activated delayed fluorescence (TADF) into ESIPT molecules
with the goals of improving their ΦPLs and increasing
their fluorescence lifetimes. Two proof-of-concept molecules, PXZPDO and DMACPDO, were developed by adopting
symmetric D−π–A−π–D molecular
architectures (where D and A represent donors and acceptors, respectively)
featuring electron-donating phenoxazine or a 9,9-dimethyl-9,10-dihydroacridine
moiety, an ESIPT core β-diketone, and phenylene π-bridges.
Both molecules exhibited sole enol-type forms stabilized by intramolecular
hydrogen bonds and exhibited a unique and dynamic ESIPT character
that was verified by transient absorption analyses. Endowed with distinct
TADF features, PXZPDO and DMACPDO showed
high ΦPLs of 68% and 86% in the film state, coupled
with notable delayed fluorescence lifetimes of 1.33 and 1.94 μs,
respectively. Employing these ESIPT emitters successfully achieved
maximum external quantum efficiencies (ηexts) of
18.8% and 23.9% for yellow and green organic light-emitting diodes
(OLEDs), respectively, which represent the state-of-the-art device
performances for ESIPT emitters. This study not only opens a new avenue
for designing efficient ESIPT emitters with high ΦPLs and long fluorescence lifetimes in solid state but also unlocks
the huge potential of ESIPT emitters in realizing high-efficiency
OLEDs.

开发兼具高固态光致发光量子产率（ΦPLs）与长荧光寿命的激发态分子内质子转移（ESIPT）发光体始终是一项极具挑战性的课题。本研究将热激活延迟荧光（TADF）的分子设计策略引入ESIPT分子，旨在提升其光致发光量子产率并延长荧光寿命。我们采用对称D−π–A−π–D分子架构（其中D与A分别代表给体与受体），设计合成了两种概念验证分子PXZPDO与DMACPDO，该架构包含给电子吩噁嗪或9,9-二甲基-9,10-二氢吖啶基团、ESIPT核心β-二酮以及亚苯基π桥。两种分子均仅呈现由分子内氢键稳定的烯醇式构型，并展现出独特且动态的ESIPT特性，该特性通过瞬态吸收分析得以验证。得益于显著的TADF特性，PXZPDO与DMACPDO在薄膜态下分别展现出68%与86%的高光致发光量子产率，以及1.33 μs与1.94 μs的可观延迟荧光寿命。将这类ESIPT发光体应用于有机发光二极管（OLEDs）时，分别实现了黄色器件与绿色器件18.8%和23.9%的最大外量子效率（ηexts），达到了当前ESIPT发光体的顶尖器件性能。本研究不仅为开发兼具高固态光致发光量子产率与长荧光寿命的高效ESIPT发光体开辟了新路径，同时也解锁了ESIPT发光体在实现高效率OLEDs中的巨大应用潜力。