A Deep Blue B,N-Doped Heptacene Emitter That Shows Both Thermally Activated Delayed Fluorescence and Delayed Fluorescence by Triplet–Triplet Annihilation

Abstract

An easy-to-access, near-UV-emitting linearly extended B,Ndoped heptacene with high thermal stability is designed and synthesized in good yields. This compound exhibits thermally activated delayed fluorescence (TADF) at ambient temperature from a multiresonant (MR) state and represents a rare example of a non-triangulene-based MR-TADF emitter. At lower temperatures triplet−triplet annihilation dominates. The compound simultaneously possesses narrow, deep-blue emission with CIE coordinates of (0.17, 0.01). While delayed fluorescence results mainly from triplet−triplet annihilation at lower temperatures in THF solution, where aggregates form upon cooling, the TADF mechanism takes over around room temperature in solution when the aggregates dissolve or when the compound is well dispersed in a solid matrix. The potential of our molecular design to trigger TADF in larger acenes is demonstrated through the accurate prediction of ΔE ST using correlated wave-function-based calculations. On the basis of these calculations, we predicted dramatically different optoelectronic behavior in terms of both ΔE ST and the optical energy gap of two constitutional isomers where only the boron and nitrogen positions change. A comprehensive structural, optoelectronic, and theoretical investigation is presented. In addition, the ability of the achiral molecule to assemble on a Au(111) surface to a highly ordered layer composed of enantiomorphic domains of racemic entities is demonstrated by scanning tunneling microscopy.

Dual emission in purely organic materials for optoelectronic applications

“…Finally, Zysman-Colman et al have recently reported an interesting deep-blue multi-resonance TADF emitter 61 with dominant TTA at low-temperatures. 127 The low-temperature 126 Copyright 2018 Springer Nature. (c) Different density plots for lowest singlet and triplet excited states for 61 calculated in the gas phase by using SCS-CC2; emission spectra of 61 in THF at 7.6 Â 10 À5 M at 300 K; PL transients of 61 taken in 7.6 Â 10 À6 M solution, excited at 355 nm, integrated between 380 and 420 nm at 300 K. Reproduced with permission.…”

“…(c) Different density plots for lowest singlet and triplet excited states for 61 calculated in the gas phase by using SCS-CC2; emission spectra of 61 in THF at 7.6 Â 10 À5 M at 300 K; PL transients of 61 taken in 7.6 Â 10 À6 M solution, excited at 355 nm, integrated between 380 and 420 nm at 300 K. Reproduced with permission. 127 Copyright 2020 American Chemical Society. TTA in this case stemmed from the presence of aggregates of 61 in THF solution upon cooling.…”

Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

“…Charge-transfer (CT) interactions between electron donors (D) and acceptors (A) are the basis of many functions of p-conjugated molecules and polymers, [1][2][3][4][5][6][7] Recently,thermally activated delayed fluorescence (TADF) polymers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] with CT emission have attracted much attention because they can convert triplet excitons to singlet ones through reverse intersystem crossing (rISC) process to realize 100 %i nternal quantum efficiency (IQE), [28][29][30][31][32][33][34][35][36][37][38][39][40][41] providing ap romising approach for developing solution-processed OLEDs without use of precious metal complexes.…”

Three‐ and Four‐Coordinate, Boron‐Based, Thermally Activated Delayed Fluorescent Emitters

“…Based on this, the molecular design strategy for pure blue or pure red MR-TADF emitters was proposed with very strong computational evidence, indicating a strategy for future design of highly efficient and pure color MR-TADF compounds. [104,105] Currently, three-coordinate, boron-derived MR-TADF emitters are the state of the art blue emitters in terms of EQE, EQE roll-off, FWHM, color purity, and possibly device lifetime. They demonstrated their potential as the leading blue emitters in the field of OLEDs, and further development may resolve all challenging issues associated with blue OLEDs.…”