Ornamenting of Blue Thermally Activated Delayed Fluorescence Emitters by Anchor Groups for the Minimization of Solid-State Solvation and Conformation Disorder Corollaries in Non-Doped and Doped Organic Light-Emitting Diodes

Motivated to minimize the effects of solid-state solvation and conformation disorder on emission properties of donor–acceptor-type emitters, we developed five new asymmetric multiple donor–acceptor type derivatives of tert-butyl carbazole and trifluoromethyl benzene exploiting different electron-accepting anchoring groups. Using this design strategy, for a compound containing four di-tert-butyl carbazole units as donors as well as 5-methyl pyrimidine and trifluoromethyl acceptor moieties, small singlet-triplet splitting of ca. 0.03 eV, reverse intersystem crossing rate of 1 × 106 s–1, and high photoluminescence quantum yield of neat film of ca. 75% were achieved. This compound was also characterized by the high value of hole and electron mobilities of 8.9 × 10–4 and 5.8 × 10–4 cm2 V–1 s–1 at an electric field of 4.7 × 105 V/cm, showing relatively good hole/electron balance, respectively. Due to the lowest conformational disorder and solid-state solvation effects, this compound demonstrated very similar emission properties (emission colors) in non-doped and differently doped organic light-emitting diodes (OLEDs). The lowest conformational disorder was observed for the compound with the additional accepting moiety inducing steric hindrance, limiting donor–acceptor dihedral rotational freedom. It can be exploited in the multi-donor–acceptor approach, increasing the efficiency. Using an emitter exhibiting the minimized solid-state solvation and conformation disorder effects, the sky blue OLED with the emitting layer of this compound dispersed in host 1,3-bis(N-carbazolyl)benzene displayed an emission peak at 477 nm, high brightness over 39 000 cd/m2, and external quantum efficiency up to 15.9% along with a maximum current efficiency of 42.6 cd/A and a maximum power efficiency of 24.1 lm/W.


S2
Instrumental 1 H (400 MHz) and 13 C (101 MHz) NMR spectra were recorded on a Varian Unity Inova 300 apparatus at ambient temperature; spectra were analysed with the MestreNova program package. Infrared (IR), melting points, thermogravimetric analysis, differential scanning calorimetry (DSC) measurements were carried out as described earlier. 1 Mass spectra were recorded on a Waters ZQ 2000 analytical system.
Elemental analysis was performed with an Exeter Analytical CE-440 Elemental Analyzer. The gas phase structures of the compounds in the ground electronic state were optimized at the DFT level using the B3LYP hybrid functional and 6-31G(d,p) basis set. The geometries of the S 1 and T 1 states were optimized using TDDFT gradients at the B3LYP/6-31G(d,p) level. All computations were carried out with the Gaussian 16 program package. 2 Cyclic voltammetry (CV) measurements were carried out as described earlier. 3 All dilute solutions of samples were prepared with concentrations of 10 -5 M for absorption and emission study. Absorption spectra were recorded at Room temperature (RT) using the UV-VIS-NIR Avantes (AvaSpec-2048XL) spectrophotometer with a 1 cm quartz cuvette. Steady state emission and timeresolved emission spectra were recorded at RT using an Edinburgh Instruments FLS980 spectrometer.
Samples were excited at 330 nm using a Xenon lamp for steady-state measurements and at 374 nm using the PicoQuant LDH-D-C-375 laser for time-resolved emission spectra. FLS980 integrating sphere was used for recording the values of photoluminescence quantum yields (PLQY) by an absolute method at room temperature. PLQY values of the neat films in oxygen-free conditions were obtained by first performing measurements in the air using an integrating sphere, and then evaluating the increase of PL intensity by placing the films in a vacuum cryostat equipped with a turbo-molecular pump and capable of achieving 10 -5 Torr pressure. Furthermore, by using the same method, the PL quantum yields for synthesized compounds in toluene under ambient and degassed conditions were measured. For preparing S3 oxygenated solutions, samples were bubbled using a compressed oxygen capsule for 10 minutes and degassed solutions were prepared via bubbling argon inert gas for 10 minutes using a quartz cuvette cell.
The singlet-triplet energy splitting (ΔE ST ) was determined from the energy difference between the onsets of the fluorescence and phosphorescence spectra of the THF solutions recorded at 77 K using UV-VIS-NIR Avantes (AvaSpec-2048XL) spectrophotometer. An integral nitrogen reservoir cryostat Optistat DN2 providing a controlled low temperature exchange gas environment was used for the characterization of photophysical properties of the samples from 77 to 300 K in inert atmosphere (N 2 ). Ionization potentials (IP PE ) of designed compounds in solid-state were estimated by the electron photoemission spectroscopy in air. 4 Time, s Current density, mA/cm 2 CN5:electrons d=6 m Figure S5. TOF signals for vacuum deposited films CN1-5 at positive (for holes) and negative (for electrons) applied voltages at ITO electrode.

AIEE
PL spectra of the dispersions of CN1-CN5 in the THF-water mixtures with various water fractions (f w ) from 0 to 90% were recorded ( Figure S9). Except CN3, emissive aggregates of the studied compounds were formed at the certain concentrations of water (f w of 50-60%) highlighting AIEE phenomenon.

Temperature dependent steady state and time resoled PL measurements.
PL spectra and PL decay curves of the neat films were recorded under inert atmosphere at the different temperatures ( Figure S10, S11). As it was expected, the typical TADF decay curves were observed. They showed the prompt fluorescence component in nanosecond range and delayed fluorescence component in microsecond range. The intensity of delayed fluorescence constantly grew up with the increase of temperature from 77 to 260 K proving the TADF nature of emission. The rate constants k ISC and k RISC were calculated at the different temperatures by taking lifetimes of prompt florescence and delayed fluorescence from the exponential fitting of TADF decays recorded at the different temperatures (Table  S6).  Figure S13. The temperature dependences of k ISC and k RISC for neat films of compounds CN2-5.