Pure Polycyclic Aromatic Hydrocarbon Isomerides with Delayed Fluorescence and Anti‐Kasha Emission: High‐Efficiency Non‐Doped Fluorescence OLEDs

Abstract Pure polycyclic aromatic hydrocarbons (PAHs) consisting solely of carbon‐hydrogen or carbon‐carbon bonds offer great potential for constructing durable and cost‐effective emitters in organic electroluminescence devices. However, achieving versatile fluorescence characteristics in pure PAHs remains a considerable challenge, particularly without the inclusion of heteroatoms. Herein, an efficient approach is presented that involves incorporating non‐six‐membered rings into classical pyrene isomerides, enabling simultaneous achievement of full‐color emission, delayed fluorescence, and anti‐Kasha emission. Theoretical calculations reveal that the intensity and distribution of aromaticity/anti‐aromaticity in both ground and excited states play a crucial role in determining the excited levels and fluorescence yields. Transient fluorescence measurements confirm the existence of thermally activated delayed fluorescence in pure PAHs. By utilizing these PAHs as emitting layers, electroluminescent spectra covering the entire visible region along with a maximum external quantum efficiency of 9.1% can be achieved, leading to the most exceptional results among non‐doped pure hydrocarbon‐based devices.


General Informations
1 H and 13 C nuclear magnetic resonance (NMR) spectra were recorded on Bruker AV 500M NMR spectrometer at room temperature, using CDCl3 or CD2Cl2 as solvent with tetramethylsilane as internal standard.High resolution mass spectrometer (HRMS) were collected on a Thermo Scientific LTQ Orbitrap XL mass spectrometer with electron spray ionization.Thermogravimetric analysis (TGA) was recorded on a TA Q50 instrument under nitrogen atmosphere with an identical heating rate of 10 o C per min from r.t. to 650 o C. The degradation temperature (Td) was estimated from the 5% weight loss.Cyclic voltammetry (CV) measurements were carried out on a CHI600 electrochemical analyzer (Chenhua, China) at room temperature, with a conventional three-electrode system consisting of a glassy carbon working electrode, a platinum wire auxiliary electrode, and an Ag/AgCl standard electrode was used as the reference electrode.The supporting electrolyte was 0.1 M tetrabutylammonium hexafluorophosphate (n-Bu4NPF6) in anhydrous dichloromethane solution, and ferrocene was additional estimated as the internal standard during the measurement.UV-Vis spectra in solution were recorded on a UV-3100 spectrophotometer at room temperature.Roomtemperature photoluminescence spectra and phosphorescence spectra were measured on a Hitachi F-7000 fluorescence spectrophotometer with xenon lamp as the light source.The absolute fluorescence quantum yields (PLQY) were measured on a Quantaurus-QY measurement system (C9920-02, Hamamatsu Photonics) equipped with a calibrated integrating sphere.During the PLQY measurements, the integrating sphere was purged with pure and dry argon to maintain an inert environment.The lifetimes of fluorescence and delayed fluorescence were performed on PicoQuant Fluotime300.

Theoretical Calculations
Density functional theory (DFT) calculations of the geometrical and electronic properties of these pure PAHs and TPE-based emitters at ground-states were performed by using Gaussian 16 software package at the B3LYP/6-311G** level including Grimme's dispersion correction. [1]The configuration optimization of the excited states of these PAHs were carried out at the same level.The nucleus-independent chemical shifts (NICS) were calculated using the gauge independent atomic orbital (GIAO) standard at B972/def2TZVP level with the consideration of SMD solvent model in chloroform.To remedy the rapidly damping of non-Coulomb part of exchange functionals at large distances, the long-range corrected functional LC-ωPBE was adopted to calculate the electron excitation energies of the TPE-modified PAHs accurately.An iteration procedure was employed to non-empirically tune the ω parameters under the optimized geometrical configuration of ground states, [2] and then the time-dependent DFT (TD-DFT) calculations were performed at the LC-ωPBE/6-311G(d,p) level of theory with tuned ω values.All calculations were performed in the gas phase, and visualized using GaussView 6.0.The wave function analysis, hole-electron analysis and visualization of twodimensional iso-chemical shielding surface (2D-ICSS) was carried out by using Multiwfn 3.8 program. [3]][7]

Device Fabrication and Characterization
The ITO coated glass substrates [ZhongNuo Advanced Material (Beijing) Technology Co., Ltd] with a sheet resistance of 15 Ω square -1 were consecutively ultrasonicated with acetone/isopropanol and dried with nitrogen gas flow, followed by 20 min ultraviolet lightozone (UVO) treatment in a UV-ozone surface processor (PL16 series, Sen Lights Corporation).
Afterwards, the ITO substrates was transferred to the deposition system.The organic layers including dipyrazino [2,3-
The synthetic route of APD-2Br was executed according to the previously reported literature [8] with appropriate modification.Initially, the starting materials of (50 mL) was injected into the flask, the combined mixture was stirred at 70 o C for another 1 day.After cooling to room temperature, the mixture was extracted with EtOAc for three times.
The combined organic layers were washed with water and brine and dried over MgSO4.
Removing the solvent under reduced pressure, the crude product was chromatographically purified on silca gel column.The eluent is pure petroleum.White solid 1,2,5,6,7,8hexahydrocyclohepta[fg]acenaphthylene (APD') was abtain by further recrystallization from DCM/MeOH via diffusion with good yield of 85%.The obtained white solid (2.80 g, 13.4 mmol), DDQ (18.34 g, 80.60 mmol), t-BuOK (15.08 g, 134.5 mmol) and toluene (260 mL, 0.05 M) was then added to a round bottom flask successively.The combined mixture was heated to 80 o C and stirring for 17 h.After cooling down, the suspension was filtered via diatomite, and the filtrate was heated under reduced pressure to remove the redundant solvent.The crude product was chromatographically purified on silca gel column with petroleum as eluant to give red solid cyclohepta[fg]acenaphthylene (APD) at a good yield of 82%.Afterwards, APD (600 mg, 2.97 mmol) was dissolved in THF (600 mL, 5 mM) in a round bottom flask.After adding NBS (1.12 g, 6.24 mmol) portionwise, the combined mixture was stirred at room temperature for 12 h.After the reaction finished, quenched it with H2O.The reacted mixture was extracted with DCM for three times.The organic layers were washed with water and brine, dried over with MgSO4.After removing the solvent under reduced pressure, the crude product was then chromatographically purified on silca gel column, using petroleum ether/DCM (3/1, v/v).
Further purification via recrystallization from DCM/MeOH to obtain the title compound APD-2Br at a considerable yield of 66%.

Synthesis of 3,8-dibromofluoranthene (FLA-2Br
). Br2 (335 mg, 2.10 mmol) was dissolved in 40 mL DCM in a dropping funnel.To a round bottom flask charged with fluoranthene (2.02 g, 1 mmol) and 60 mL DCM, the Br2 dilute solution was then dropped slowly into the aforementioned mixture.The suspension was stirred at room temperature over night.After quenching with Na2S2O3, the combined mixture was filterd, and the residue was wash with EtOH, DCM successively affording faint yellow solid with a desirable yeild of 85%. was then added into the solution slowly, the combined mixture was stirred at room temperature for 12 h.After the complete reaction, quenched it with H2O and extracted with DCM for three times (50 mL * 3).The collected organic layers was washed with water and brine, dried over with MgSO4.After removing the solvent under reduced pressure, the crude product was chromatographically purified on silca gel column, using n-hexane as eluent.Further purification was carried out via recrystal from DCM/MeOH to obtain the title compound as red solid (yield 25%). 1  were added successively.Subsequently, 40 mL toluene, 10 mL water and 10 mL of ethanol was added via syringe, and the mixted suspension was deoxygenated via sustained bubbling with argon.The mixture was allowed to stir at 110 o C for 16 hours.After cooling down, the reaction mixture was poured into 300 mL water and extracted with dichloromethane for three times.The collected organic layers is washed with brine and dried over with sodium sulfate.After the solvent was removed under reduced pressure, the crude product was purified by using column chromatography with silica gel as immobile phase and dichloromethane/petroleum ether (v/v = 1/3) as eluent.Further purification was executed by using recrystallization in dichloromethane/methanol mixture, and followed by vacuum sublimation to afford the target pure hydrocarbon emitters with high purity.
The purification of TPE-16Py was executed with following procedure: after colling down, the obtained suspension was treated with direct filtration, and the residues was washing with a mass of acetone, hot dichloromethane, chloroform, toluene, respectively, and then followed with       13 Table S3.Calculated key parameters involved in the hole-electron analysis.

Figure S2 .
Figure S2.Distortionless enhancement by polarization transfer (DEPT) analysis of the Py.
, H and t indices refer to the distance of charge transfer between the hole and the electron, integral of Sr function overlap, function of hole and electron, separation of hole and electron distributions, respectively.Ecoul refer to the coulomb attractive energy between the hole and electron, HDI and EDI, represent for the hole and electron delocalization index, respectively.

Figure S9 .
Figure S9.Density difference maps of these PAHs during the electron excitations from ground states to corresponding singlet excited states (red refer to density decrease, blue refer to density increase).

Figure S10 .Figure S11 .Figure S12 .Figure S13 .
Figure S10.Hole-electron analysis of S0→S1 transition for a) FLA, b) APD and c) DCH, respectively.With the sequence of atomic contributions to hole and electron in terms of heat map, distribution of hole and electron on molecular skeleton at the same time (green represents the electron distribution, and blue represents the hole distribution), MOs with contribution to hole or electron higher than 1%.