A Simple Molecular Design Strategy for Delayed Fluorescence toward 1000 nm

Abstract

Harnessing the near-infrared (NIR) region of the electromagnetic spectrum is exceedingly important for photovoltaics, telecommunications, and the biomedical sciences. While thermally activated delayed fluorescent (TADF) materials have attracted much interest due to their intense luminescence and narrow exchange energies (ΔEST), they are still greatly inferior to conventional fluorescent dyes in the NIR, which precludes their application. This is because securing a sufficiently strong donor–acceptor (D–A) interaction for NIR emission alongside the narrow ΔEST required for TADF is highly challenging. Here, we demonstrate that by abandoning the common polydonor model in favor of a D–A dyad structure, a sufficiently strong D–A interaction can be obtained to realize a TADF emitter capable of photoluminescence (PL) close to 1000 nm. Electroluminescence (EL) at a peak wavelength of 904 nm is also reported. This strategy is both conceptually and synthetically simple and offers a new approach to the development of future NIR TADF materials.

Modulation of charge transfer by N-alkylation to control photoluminescence energy and quantum yield

“…[42][43][44] This approach can be applied broadly to N-heterocycles, which are pervasive structural motifs in many organic chromophores. Resulting insights into their CT excited states will progress our understanding of natural photoactive systems [16][17][18]45 and improve the performances of emissive [2][3][4][5][6][7]39 and light-absorbing [46][47][48] devices. The kinetic stabilities of the N-alkylated compounds open up the possibility of quaternizing the chromophores selectively at sites other than their most basic N site, achieving structures that are inaccessible by protonation, while the choice of counterion can serve as a handle to control physical properties.…”

“…1 This prediction of an extensive eld of research has held true through the continued use of spectroscopy to study epipolic dispersion that, also thanks to Stokes, we now know as uorescence. In recent years, uorescence spectroscopy has been used to characterize a wide range of different compounds and uncover new functional phenomena such as thermally activated delayed uorescence (TADF), [2][3][4][5][6][7] aggregation induced emission [8][9][10] and room temperature phosphorescence. [11][12][13] TADF is of particular interest as it increases the efficiency of organic light-emitting diodes (OLEDs) used in displays and devices.…”

Organic Long‐Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound

“…AP has previously been employed in red TADF emitter design and based on its rigid character, OLEDs using AP‐based emitters show high efficiency. [ 19–22 ] The related molecular structures and performance of these AP‐based emitters are summarized in Table S1, Supporting Information. Here, the DFT and TDDFT calculations show that CzPhAP possesses a large calculated ∆ E ST of 0.18 eV ( Figure a).…”

Devising Efficient Red‐Shifting Strategies for Bioimaging: A Generalizable Donor‐Acceptor Fluorophore Prototype

“…The HOMO electron density is mainly localized at the donor moiety while LUMO shows charge transfer character . Notably, one may encounter two ICT scenarios: one with the electron density delocalized over both the donor and acceptor moieties, and the other with the electron density largely localized at the acceptor moiety . Most donor‐acceptor dyes adopt one or the other, but in some cases both are present and the globally delocalized ICT state lies lower in energy than the acceptor‐localized ICT state .…”