Organic Long‐Persistent Luminescence from a Thermally Activated Delayed Fluorescence Electron Donor‐Acceptor Binary System

Abstract

Organic long‐persistent luminescence (OLPL) based on long‐lived charge‐separated (CS) states shows considerable emission persistence time owing to the ability to store absorbed photon energy. Herein, a novel electron donor‐acceptor (D–A) binary system consisting of electron donor 4,4,4‐tris[3methylphenyl(phenyl)amino]triphenylamine and electron acceptor tris‐[3‐(3‐pyridyl)mesityl]borane is designed and investigated for outstanding OLPL performance. It is found that the proposed binary system exhibits effective OLPL emission that lasted for more than 100 s after 1 min of ultraviolet light irradiation at room temperature (292 K). Moreover, this electron D–A binary system also exhibits thermally activated delayed fluorescence emission prior to OLPL emission. Both emission types are found to be temperature‐sensitive, which are believed to result from the occurrence of reverse intersystem crossing and the formation of a CS state, respectively. The findings enrich the electron D–A system OLPL materials and clarify the rich excited‐state transitions during OLPL emission of electron D–A systems.

Influence of Intermolecular Structural Effects on Radiative Efficiency in Xanthene-Based Carboranyl Luminophores

“…13 Generally, this strategy prevents the formation of locally excited (LE) states with long radiative lifetimes, thus enhancing luminescence efficiency. 10,14,15 o-Carboranes have a three-dimensional framework with high polarizability owing to their σ-aromaticity, 16,17 a strong electron-withdrawing effect on C-substituents, 18−21 which surpasses that of fluorine, 22,23 and high thermal and electrochemical stabilities due to their closed structure. Consequently, they are highly sought after as functional groups in optoelectronic materials and hold great potential as electron acceptors.…”

“…The development of organic and organometallic luminophores simultaneously exhibiting electrochemical stability and high luminescence efficiency remains critical for various applications, including organic light-emitting diodes, − chemosensors, − and photovoltaic cells. − Such luminophores are typically constructed by connecting electron-rich donor (D) groups to electron-poor acceptor (A) groups to form D–A dyad systems − and thus induce emission based on intramolecular charge transfer (ICT) . Generally, this strategy prevents the formation of locally excited (LE) states with long radiative lifetimes, thus enhancing luminescence efficiency. ,, o -Carboranes have a three-dimensional framework with high polarizability owing to their σ-aromaticity, , a strong electron-withdrawing effect on C-substituents, − which surpasses that of fluorine, , and high thermal and electrochemical stabilities due to their closed structure. Consequently, they are highly sought after as functional groups in optoelectronic materials and hold great potential as electron acceptors. − The emission efficiency of D–A-type luminophores with aromatic D groups and o -carboranyl A groups is strongly influenced by their molecular geometry. − In particular, the efficiency of ICT-based emission is significantly affected by the rotation of the o -carborane moiety relative to the aromatic ring plane, a phenomenon known as twisted intramolecular charge transfer (TICT). − This behavior is due to the fact that the ICT-based transition occurs through an exo -π-interaction between π-delocalized region of the aromatic group and the tangential p -orbital on the carbon of the appended o -carborane, with the magnitude of this interaction depending on the degree of orthogonality between the o -carborane C–C bond and aromatic plane. − For example,...…”