Solution-Processed Dendrimer-Based TADF Materials for Deep-Red OLEDs

Abstract

We report the first example of a thermally activated delayed fluorescence (TADF) poly(dendrimer), composed of a norbornenyl-derived polymer backbone and dendritic side-chain chromophores comprising 2,3-dicyanopyrazino as the electron acceptor and a first-generation fluorenylcarbazole derivative as the electron donor. The TADF poly(dendrimer) homopolymer, with one dendritic side chain attached to each monomer unit, emitted deep-red light. The emission of the poly(dendrimer) was found to be red-shifted relative to the nonpolymeric doubly dendronized emitter composed of the same components. The simple dendrimer was found to have a solution photoluminescence quantum yield (PLQY) of around 70%. In contrast, the poly(dendrimer) had a PLQY of 9%, which was attributed to intramolecular interchromophore interactions. An interesting feature of the poly(dendrimer) was that oxygen did not quench the TADF emission. We found that the PLQY of the simple dendrimer decreased markedly in neat films, whereas that of the poly(dendrimer) did not, with both having a solid-state PLQY of around 10%. The results suggest that intrapolymer chromophore−chromophore interactions observed in solution for the poly(dendrimer) were similar to the intermolecular chromophore−chromophore interactions of the dendrimer in the solid state. Simple two-layer organic light-emitting diodes comprising nondoped films of the materials and an electron transport layer showed red emission with CIE coordinates of (x > 0.66, y < 0.34). The dendrimer-based device had a maximum external quantum efficiency of 2.4%, which is among the best for solution-processed deep-red emissive TADF-based OLEDs but in a simpler device architecture.

Emissive Material Optimization for Solution-Processed Exciplex OLEDs

“…A He–Cd laser was used for excitation at 325 nm, and the beam power was around 0.2 mW. Temperature and time-resolved PL spectra and decay were collected with a home-built spectrometer . The system consisted of an ICCD camera (Andor New iStar ICCD) and a photomultiplier tube (Hamamatsu; H10721-21) connected to an oscilloscope (Teledyne; 1 GHz, WaveSurfer 510) to measure the time-resolved PL spectra and integrated PL decay, respectively.…”

“…Temperature and time-resolved PL spectra and decay were collected with a home-built spectrometer. 29 The system consisted of an ICCD camera (Andor New iStar ICCD) and a photomultiplier tube (Hamamatsu; H10721-21) connected to an oscilloscope (Teledyne; 1 GHz, WaveSurfer 510) to measure the time-resolved PL spectra and integrated PL decay, respectively. The optics were arranged to collect the emitted light at a right angle to the laser path, which along with 400 nm long-pass filters were used to minimize the effect of the scattered excitation on the emission measurement.…”

Thiol-Ene Click-Inspired Late-Stage Modification of Long-Chain Polyurethane Dendrimers

“…Dendrimers are highly branched, multivalent, star-shaped polymeric macromolecules [1][2][3][4]. These monodispersed dendritic polymers exhibit wide applications in the field of catalysis, sensing, molecular electronics, photonics, fluorescence, and therapeutics [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. After Tomalia's first report on poly(amidoamine) (PAMAM) dendrimers in 1985, ref [21] many research groups have reported the synthesis of dendritic macromolecules using ether, ester, carbosilane, amide, and alkyne linkages [21][22][23][24][25][26][27][28][29][30][31][32][33].…”

Thiol-Ene Click Inspired Late-Stage Modification of Long-Chain Polyurethane Dendrimers

“…[1][2][3][4] These monodispersed dendritic polymers exhibit wide applications in the field of catalysis, sensing, molecular electronics, photonics, fluorescence, and therapeutics. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] After Tomalia's first report on poly(amidoamine) (PAMAM) dendrimers in 1985, 20 many research groups have reported the synthesis dendritic macromolecules using ether, ester, carbosilane, amide, and alkyne linkages. [21][22][23][24][25][26][27][28][29][30][31][32][33] Nevertheless, very few have reported the synthesis of dendrimers having urethane linkage.…”