Thermally Activated Delayed Fluorescence in 1,3,4-Oxadiazoles with π-Extended Donors

Abstract

Here, we describe the synthesis of five 1,3,4oxadiazole-based donor−acceptor materials, using dendritic carbazole-based donors 9′H-9,3′:6′9″-tercarbazole (terCBz) and N3,N3,N6,N6-tetra-p-tolyl-9H-carbazole-3,6-diamine (TTAC). Due to the strongly donating and highly twisted nature of the TTAC donor as well as the spatially separated hole−particle wavefunctions, three of the five compounds exhibited thermally activated delayed fluorescence (TADF) in spite of a relatively large ΔE ST measured through phosphorimetry (0.33−0.37 eV). These materials demonstrated photoluminescence quantum yields as high as 0.89 in toluene, with emission maxima ranging from 474 to 495 nm in the solid state. Additionally, two materials containing only terCBZ donor(s) exhibited deep blue fluorescence, with Commission Internationale de l'ećlairage coordinates of (0.16, 0.05); the weaker nature of the terCBz donor results in a prohibitively large ΔE ST (0.68−0.77 eV). A gap-tuned range-separated hybrid functional (ωB97XD*) was used to rigorously calculate triplet energies, while a systematic analysis of electronic structures and photophysical properties provided further insight into the properties of these materials. These findings ultimately contribute a synthetically facile approach toward highly emissive TADF emitters using a 1,3,4-oxadiazole motif.

2,3‐Disubstituted Fluorene Scaffold for Efficient Green Phosphorescent Organic Light‐Emitting Diodes

“…Consequently, the corresponding optical energy gaps ( E g s) are estimated from those values to be 3.29, 3.32, 3.33 and 3.42 eV, respectively. As provided in PL spectra, four materials all show unstructured and broad emission curves, which suggests that their singlet excited states display charge transfer (CT) features [92,93] . Their PL spectra peak at the wavelengths of 492, 434, 491 and 439 nm for 2TRz3TPA, 2TRz3Cz, 2TPA3TRz and 2Cz3TRz, respectively.…”

“…As provided in PL spectra, four materials all show unstructured and broad emission curves, which suggests that their singlet excited states display charge transfer (CT) features. [92,93] Their PL spectra peak at the wavelengths of 492, 434, 491 and 439 nm for 2TRz3TPA, 2TRz3Cz, 2TPA3TRz and 2Cz3TRz, respectively. The red-shifts in PL spectra of TPA-based materials (2TRz3TPA and 2TPA3TRz) compared to PhCz-based materials (2TRz3Cz and 2Cz3TRz) are correlated with the relative strong electron-donating ability of TPA.…”

Effect of Oxidation on the Chiroptical Properties of Sulfur-Bridged Binaphthyl Dimers

“…NTOs provide a realistic interpretation of relevant photophysical transitions leading to the S 1 state. Locally excited transitions appear to be present in all compounds, which is a prominent feature for structurally symmetric compounds …”

“…Locally excited transitions appear to be present in all compounds, which is a prominent feature for structurally symmetric compounds. 50 TD-DFT calculations were performed on both the optimized ground state (S 0 ) and excited state (S 1 ) structures. This allows for the simulation of spectroscopic data and calculation of theoretical absorbance and luminescent dis-symmetry factors (|g|) (Figure S5).…”

Efficient Non‐Doped Blue Electro‐fluorescence with Boosted and Balanced Carrier Mobilities

“…Last but not the least, the fluorene bridge can not only enlarge the D-A overlap but also increase the D-A distance to regulate the CT excited-state component, which is both positive to the enhancement of the PLQY and can also solve the problem of the too large bandgap between CZ and OXZ (around 3.1 eV). [21][22][23][24][25] More importantly, the extended π-conjugation can also give rise to the regulated molecular stacking, which is beneficial to the effective carrier transmission in non-doped OLED. Additionally, to avoid the aggregation quenching to the best extent, we choose the 9-propyl substituted fluorene as the π-bridge to increase the steric hindrance in the neat film of the D-π-A materials.…”