Electron‐Rich Twistacene‐Modified Arylboron Donor–Acceptor Systems: Synthesis, Photophysics, and Electroluminescence with Hot Exciton Response

Abstract

A series of twistacene‐functionalized donor (D)‐π‐acceptor (A) derivatives (2–5) have been designed and synthesized, in which twistacene can be regarded as a promising platform for electron‐rich systems for fluorescence emitters. The connecting modes and various acceptors are also examined to investigate the effect of structural changes on the photophysical, electrochemical, and thermal properties. The strong electron‐withdrawing capability of the arylboron‐modified benzonitrile unit can effectively separate the HOMO and LUMO energy levels of 4/5, which is beneficial for the formation of thermally activated delayed fluorescence (TADF) molecules. Cyan and orange organic light‐emitting diodes based on 4 and 5 exhibit promising electroluminescence with a maximum brightness of 7643 cd m−2 for device‐4 and 14871 cd m−2 for device‐5.

Pentagon-Containing π-Expanded Systems: Synthesis and Photophysical Properties

“…The results suggest that the incorporation of a cyclopenta ring can reduce the LUMO level and the potentials are significantly affected by the molecular cores. [39][40][41]51,52 In addition, similar change trends of the band gaps are observed in the data from DFT calculations and optical spectra.…”

Synthesis, Photophysics and Optical Limiting Properties of Functionalized Benzofuran Derivatives

“…Upon changing the solvent from toluene (ɛ = 2.4) to tetrahydrofuran (THF, ɛ = 7.4), to dichloromethane (ɛ = 8.9), then to DMF (ɛ = 36.7), the maxima emission spectra are bathochromic-shifted from 491 nm to 505 nm, to 526 nm, then to 536 nm, while there are negligible changes for the absorption spectra (Figure S1), indicating an ICT process. [42,43] 2 a/2 b and 4 a/4 b display similar fluorescence contours with the emission bands at 387/408/431/456 nm and 515 nm respectively, falling into the violet and green regions (Figure 2b/c). In comparison, 3 a/3 b bearing electron-withdrawing units and electron-donating unit possess weak emission intensity in organic solvents, which might be assigned to its strongest ICT.…”

“…As shown in Figure 2, the absorption peaks of 2 a / 2 b , 3 a / 3 b , 4 a / 4 b are centered at 316/343/358/384/401 nm for 2 ( 2 a , 358 nm, 3.23×10 4 M −1 ; 2 b , 358 nm, 3.76×10 4 M −1 ), 329/344/467 nm for 3 ( 3 a , 344 nm, 2.06×10 4 M −1 ; 3 b , 344 nm, 2.06×10 4 M −1 ) and 338/352/446 nm for 4 ( 4 a , 446 nm, 1.08×10 4 M −1 ; 4 b , 446 nm, 1.08×10 4 M −1 ), respectively. Upon changing the solvent from toluene ( ϵ =2.4) to tetrahydrofuran (THF, ϵ =7.4), to dichloromethane ( ϵ =8.9), then to DMF ( ϵ =36.7), the maxima emission spectra are bathochromic‐shifted from 491 nm to 505 nm, to 526 nm, then to 536 nm, while there are negligible changes for the absorption spectra (Figure S1), indicating an ICT process [42,43] . 2 a / 2 b and 4 a / 4 b display similar fluorescence contours with the emission bands at 387/408/431/456 nm and 515 nm respectively, falling into the violet and green regions (Figure 2b/c).…”

“Hot exciton” fluorescence and charge transport of fine-tuned twistacenes: theoretical study on substitution effect and intermolecular interactions

“…To determine the performance of organic semiconductor materials in electronics applications, the carrier mobility, defined as the ratio between the velocity of the hole/electron transport and the amplitude of the electric field, is the key characteristic. 22 Therefore, detailed atomic investigations of twistacenes are needed for their precise synthesis and further use in blue fluorescent emitters, 23 nonlinear optical materials, 24,25 promising “hot exciton” TADFs 26 and OLEDs. 27,28…”

“…38. More recently, Xiao et al 26 introduced the electron-withdrawing arylboron unit into 1-H and synthesized new twistacenes 4 and 5 by sophisticated procedures. The electron-withdrawing effect of the cyano-modified triarylboron acceptors resulted in changes in electronic structures, redshift of the UV-vis peaks and small energy differences between the second excited singlet (S2) and second/third triplet (T2/3) states, resulting in these two compounds exhibiting “hot exciton” TADF properties through the RISC process.…”