# A Chiral Propeller-Shaped Triple Helicene Shows Multi-Resonant Thermally Activated Delayed Fluorescence

Jingxiang Wang,ª Jhon Sebastian Oviedo Ortiz,ᵇ Aidan P. McKay,ª David B. Cordes,ª Jeanne Crassous,ᵇ and Eli Zysman-Colman*ª

ª Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, Fife, UK, KY16 9ST

Fax: +44-1334 463808; Tel: +44-1334 463826, e-mail: eli.zysman-colman@st-andrews.ac.uk

ᵇ University of Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) – UMR 6226, F-35000 Rennes, France

Dedicated to Prof. Marcel Mayor on the occasion of his 60th birthday.

© 2024 The Authors. Helvetica Chimica Acta published by Wiley-VHCA AG. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Multi-resonant thermally activated delayed fluorescence (MR-TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller-shaped chiral MR-TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co-parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at $\lambda_{PL}$ of 491 nm, with a full width at half maximum of 52 nm and has a moderate $\Delta E_{ST}$ value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor $|g_{abs}|$ of $6.8 \times 10^{-4}$ at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C₃-symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.

**Keywords:** Chirality, helicene, circular dichroism, circularly polarized luminescence, multi-resonant thermally activated delayed fluorescence.

## Introduction

Many chiral helicenes show interesting chiroptical properties and these materials have been widely investigated in such diverse fields as bioimaging, optical data storage, optical spintronics applications, and circularly polarized organic light-emitting diodes (CP-OLEDs).[1-8] Most emissive chiral helicenes are fluorescent, but for efficient OLEDs, triplet excitons need to be harvested, so helicenes that emit either phosphorescence or thermally activated delayed fluorescence (TADF) would be potentially attractive emitters. Organic multi-resonant TADF (MR-TADF)

materials have attracted particular attention as emitters for OLEDs as not only can devices attain 100% internal quantum efficiency (IQE) but they also show narrowband emission and high photoluminescence quantum yield ($\Phi_{PL}$).[9-12] Thus, the development of chiral MR-TADF emitters would be particularly attractive for CP-MR-TADF OLEDs.

The extent of electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) from chiral emitters can be quantified by the absorption and luminescence dissymmetry factors, $g_{abs}$ and $g_{PL}$, which are defined by equation 1 and 2, respectively:

$$g_{abs} = 2 \frac{(\epsilon_L - \epsilon_R)}{(\epsilon_L + \epsilon_R)} \qquad (1)$$

Supporting information for this article is available on the WWW under https://doi.org/10.1002/hlca.202400129
$$g_{PL} = 2 \frac{(I_L - I_R)}{(I_L + I_R)} \qquad (2)$$

where $\varepsilon_L$ and $\varepsilon_R$ are the molar absorptivity coefficients associated with left- and right-handed circularly polarized light, respectively. $I_L$ and $I_R$ correspond to the intensities of the emitted left- and right-handed light, respectively. $g_{PL}$ values of -2 or 2 indicate 100% right- or left-handed CPL. As the CPL is related to the transition between excited states and ground state of the emitter, the $g_{PL}$ of a chiral molecule is dependent on the magnitude of the magnetic and electric transition dipole moments and their relative orientation according to equation 3:

$$g_{PL} = \frac{4|\mu| |m|}{|\mu|^2 + |m|^2} \cos\theta \qquad (3)$$

where $\mu$ and $m$ refer to the electric transition dipole moment and magnetic transition dipole moment vectors between the emissive excited state and the ground state, respectively, and $\theta$ is the angle between $\mu$ and $m$. [13,14] For closed shell organic small molecules, including MR-TADF emitters, $|\mu|$ is roughly 300 times larger than $|m|$, which results in very small $g_{PL}$ values, typically less than $10^{-2}$ [13]. Given the large electric transition dipole moment, equation 3 can be simplified to equation 4:

$$g_{PL} \approx \frac{4|m|}{|\mu|} \cos\theta \qquad (4)$$

It therefore becomes clear that to enhance $g_{PL}$ requires a combination of higher $|m|$ and lower $|\mu|$ and a parallel arrangement between them. Unfortunately, the planar geometries of most MR-TADF materials, including MR-TADF helicenes, result in a nearly perpendicular arrangements between $m$ and $\mu$ (Figure 1), which result in low absolute values of $\cos\theta$ and low $g_{PL}$ values of $<3 \times 10^{-3}$ (Figure S24). [15–24] However, if two identical MR-TADF helicenes are fused into one $C_2$-symmetric dimer molecule, the integrated $\mu$ and $m$ of the dimeric emitter would be parallel or anti-parallel to each other (Figure 1). [25–28] A large $\cos\theta$ value of 1 would certainly contribute to a higher $g_{PL}$ value. Based on this strategy, in particular, Guo et al. developed BN[9]H, which has the highest $|g_{PL}|$ value of $5.8 \times 10^{-3}$ in toluene among all the reported chiral MR-TADF helicenes (Figure 1). [28] The CP-OLEDs with P-BN[9]H achieved both high EQE$_{max}$ of 35.4% and

electroluminescence dissymmetry factor, $g_{EL}$, value of $6.2 \times 10^{-3}$.

With the goal of increasing $g_{PL}$, we designed a $C_3$-symmetric MR-TADF helicene DiKTa3 (Figure 2) that we calculated to have co-parallel $\mu$ and $m$ and thus a high predicted $g_{PL}$ value. DiKTa3 emits at $\lambda_{PL}$ of 491 nm (FWHM of 52 nm/0.26 eV) and has a moderate $\Delta E_{ST}$ value of 0.24 eV in toluene and is very poorly emissive. The 1 wt% doped film of DiKTa3 in PMMA exhibits TADF. The density functional theory calculated (M062X/6-31G(d,p)) [29,30] chiroptical properties based on the optimized geometry predict $g_{abs}$ values of $2.1 \times 10^{-2}$ for the $S_0-S_1$ transition due to a $\cos\theta$ value of 1. However, the predicted value differs considerably from the measured one in toluene ($g_{abs}$ of $6.8 \times 10^{-4}$). This is the result of DiKTa3 adopting a conformation that is not $C_3$-symmetric; indeed, the calculated $g_{abs}$ value using geometry obtained from the single crystal structure is $8.1 \times 10^{-4}$. This work demonstrates how a small change in the geometry of a helicene results in a large difference in the transition dipole moments and the corresponding $g_{abs}$ value. These results may also explain why many triple helicenes show low $g_{abs}$ values of around $10^{-3}$ [31].

## Results & Discussion

### Synthesis

The synthesis of DiKTa3 is shown in Figure 2a. The intermediate **1** was prepared through a palladium-catalyzed Buchwald-Hartwig amination between 1,3,5-tribromobenzene and aniline in 72% yield, which was then reacted with dimethyl 2-bromoisophthalate through an Ullmann coupling reaction to afford **2** in 68% yield. Then intermediate **2** was hydrolyzed to the acid, activated using thionyl chloride, which then cyclized via Friedel-Crafts acylation to afford DiKTa3 in a yield of 8%. The identity and purity of DiKTa3 and the intermediates were determined by melting point analysis, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry (HRMS), high-performance liquid chromatography (HPLC), and elemental analysis (EA) (Figure S1–S15). The structure of DiKTa3 was confirmed by single crystal X-ray diffraction (Figure 2b) with X-ray quality crystals obtained from slow evaporation of a THF: MeOH solution. The compound crystallizes as a mixture of (P,P,P)- and (M,M,M)-enantiomers. The conformation distorts away from planarity due to the large steric hindrance between the three DiKTa blades, which results in a propeller-shaped triple
<figure><img src="image_1.png" /></figure>

<figure><img src="image_2.png" /></figure>

## Monomer MR-TADF helicenes:

<figure><img src="image_3.png" /></figure>

$$|g_{\text{PL}}| = 5.2 \times 10^{-4}$$

**BN-Py**

<figure><img src="image_4.png" /></figure>

$$\theta = 107.3^{\circ} \\ |\cos \theta| = 0.30$$

Adv. Mater. **2023**, *35*, 2305125

<figure><img src="image_5.png" /></figure>

$$|g_{\text{PL}}| = 1.3 \times 10^{-3}$$

**Spiro-BNCz**

<figure><img src="image_6.png" /></figure>

$$\theta = 79^{\circ} \\ |\cos \theta| = 0.19$$

Aggregate **2023**, *5*, e445

<figure><img src="image_7.png" /></figure>

$$|g_{\text{PL}}| = 1.4 \times 10^{-3}$$

**RBNN**

<figure><img src="image_8.png" /></figure>

$$\theta = 109.7^{\circ} \\ |\cos \theta| = 0.34$$

Adv. Mater. **2024**, *36*, 2307420

<figure><img src="image_9.png" /></figure>

$$|g_{\text{PL}}| = 1.5 \times 10^{-3} \quad \theta = 70^{\circ}$$

**DB-S**

<figure><img src="image_10.png" /></figure>

$$|\cos \theta| = 0.34$$

Adv. Mater. **2024**, *36*, 2308314

## Dimer MR-TADF helicenes:

<figure><img src="image_11.png" /></figure>

$$|g_{\text{PL}}| = 2 \times 10^{-3}$$

**R-BN**

<figure><img src="image_12.png" /></figure>

$$\theta = 0^{\circ} \\ |\cos \theta| = 1$$

J. Am. Chem. Soc. **2021**, *143*, 17958

<figure><img src="image_13.png" /></figure>

$$|g_{\text{PL}}| = 5.8 \times 10^{-3}$$

**BN[9]H**

<figure><img src="image_14.png" /></figure>

Angew. Chem. Int. Ed. **2024**, e202401835

## This work (Trimer MR-TADF helicene):

<figure><img src="image_15.png" /></figure>

**DiKTa3**

Proposed parallel **μ** and **m**

<figure><img src="image_16.png" /><figcaption>**Figure 1.** Structures and calculated angle $\theta$ between transition dipole moments of examples of monomer and dimer MR-TADF helicenes and molecular design of **DiKTa3**.</figcaption></figure>
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /><figcaption>**Figure 2.** (a) Synthesis scheme of **DiKTa3**. (b) Face and side-on thermal ellipsoid plots of the structure of **DiKTa3**. Ellipsoids are displayed at the 50% probability level, hydrogens are omitted for clarity.</figcaption></figure>

helicene with similar torsion angles C6–C1–N1–C16, C4–C5–N5–C44 and C2–C3–N3–C30 of 38.4(7), 35.7(8) and 42.8(8)°, respectively. The **DiKTa** blades are also bent along their length with the angle between the two C₆ rings of each arm being 16.1(2), 17.2(3), and 22.7(3)°.

## Theoretical Calculations

The optimized geometry of the ground state and its electronic structure of **DiKTa3** were calculated using Density Functional Theory (DFT) at the PBE0/6-31G(d,p) level, starting from a structure drawn and optimized using Chem3D (*Figure 3a*).[30,32] The highest occupied molecular orbital (HOMO) of **DiKTa3** is located on two of the DiKTa blades while the lowest unoccupied molecular orbital (LUMO) is distributed across the whole molecule. The calculated HOMO and LUMO energies of **DiKTa3** are −6.42/−2.72 eV. Both orbitals are more stabilized than the parent **DiKTa** (HOMO of −6.20 and LUMO of −2.23 eV) and the double helicene **Hel-DiDiKTa** (HOMO of −6.26 and LUMO of −2.53 eV).[17,33] The excited-state energies were calculated using time-dependent DFT (TD-DFT) within the Tamm-Dancoff approximation (TDA) at the PBE0/6-31G(d,p) level. The S₁ and T₁ energies of **DiKTa3** are calculated to be 2.85/2.43 eV, with ΔE<sub>ST</sub> of 0.42 eV. There are six triplet states below the S₁ state,

which may participate in the RISC process.[34–36] The SOC matrix elements (SOCME) between S₁ and T₁ to T₆ transitions are calculated to be 4.20, 1.74, 1.15, 1.46, 2.10 and 1.73 cm⁻¹, based on the optimized T₁ geometry, respectively (*Figure 3a*). These values are close to those of the parent **DiKTa** (1.26, 6.66, 9.34 and 6.84 cm⁻¹ for S₁–T₁, S₁–T₂, S₁–T₃ and S₁–T₄ transitions, respectively, *Figure S16*). It is known that TD-DFT calculations overestimate ΔE<sub>ST</sub>, and so spin-component scaling second-order algebraic diagrammatic construction (SCS-(ADC)2/cc-pVDZ) calculations were undertaken as these account for higher order electronic excitations.[37,38] As shown in *Figure 3b*, **DiKTa3** shows short range charge transfer (SRCT) character with the typical alternating increasing and decreasing electron density pattern on the center of the molecule for both S₁ and T₁. The S₁ and T₁ energies of 2.72 and 2.58 eV are much more stabilized compared to those of **DiKTa** (S₁=3.46 eV and T₁=3.20 eV).[39] The corresponding ΔE<sub>ST</sub> value is calculated to be 0.14 eV.

## Optoelectronic Properties

Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of **DiKTa3** in degassed DCM with 0.1 M [nBu₄N]PF₆ as the supporting electrolyte and Fc/Fc⁺ as the internal reference (0.46 V vs. SCE)[40] were meas-
<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /><figcaption>**Figure 3.** (a) Calculated electron density distribution (isovalue: 0.02) of the HOMO, LUMO and energy levels in the gas phase based on optimized ground-state geometry and SOCME based on optimized $T_1$ geometry at the PBE0/6-31G(d,p) level. (b) Difference density plots and energies of $S_1$ and $T_1$ calculated in the gas phase at SCS-(ADC)2/cc-pVDZ level (Blue indicates an area of decreased electron density while yellow indicates increased electronic density between the ground and excited states).</figcaption></figure>

ured to experimentally determine the HOMO and LUMO energy levels (Figure S17). **DiKTa3** shows a reversible reduction wave and an irreversible oxidation wave, electrochemical behavior that is consistent with that of **DiKTa**.[³³] The reduction potential, $E_{red}$, and oxidation potential, $E_{ox}$, of **DiKTa3**, obtained from the peak values in the DPV are –1.02 and 1.83 V vs. SCE. Both values are cathodically shifted compared to **DiKTa** ($E_{red}$ of –1.34 V and $E_{ox}$ of 1.78 V vs. SCE)[³³] and

closer to those of **Hel-DiDiKTa** ($E_{red}$ of –1.16 V and $E_{ox}$ of 1.81 V vs. SCE).[¹⁷] The corresponding HOMO and LUMO energies are –6.17 and –3.32 eV with energy gap $\Delta E$ of 2.85 eV (Table S1).

The ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectra of **DiKTa3** in toluene at room temperature are shown in Figure 4a. The lowest-energy absorption band is at 450 nm and has a molar absorptivity of $1.6 \times 10^4 \text{ M}^{-1} \text{ cm}^{-1}$, values that resemble

<figure><img src="image_23.png" /><figcaption>**Figure 4.** (a) UV-vis absorption and PL spectra of **DiKTa3** in toluene at 300 K; Inset: photo of **DiKTa3** in toluene excited at 365 nm. (b) PL spectra of **DiKTa3** in different solvents at 300 K. ($\lambda_{exc}$ = 430 nm).</figcaption></figure>
<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>

those of **Hel-DiDiKTa** (453 nm, 1.4×10⁴ M⁻¹ cm⁻¹)[¹⁷] and can be assigned to the S₀–S₁ transition. The red-shifted band and lower molar absorptivity compared to that in **DiKTa** (433 nm, 2.1×10⁴ M⁻¹ cm⁻¹)[³³] align with the trends of the calculated oscillator strength and energy of the S₀–S₁ transition (2.72 eV and 0.0016 for **DiKTa3** and 3.46 eV and 0.20 for **DiKTa**).[³⁹] **DiKTa3** emits at λ<sub>PL</sub> of 491 nm, shows narrowband emission, with a FWHM of 52 nm/0.26 eV, and has a small Stokes shift of 38 nm/0.21 eV in toluene. Its emission is red-shifted compared to **DiKTa** (453 nm) and **Hel-DiDiKTa** (473 nm).[¹⁷] The shoulder emission band peaking at 515 nm and the higher-intensity absorption band at 429 nm (2.4×10⁴ M⁻¹ cm⁻¹) may come from the transitions between different vibrational energy levels as the PL spectra remain unchanged as a function of changing excitation wavelengths between 405–455 nm (Figure S18). In addition, the energy of the emission band is insensitive to solvent polarity, which indicates that its SRCT state has significant locally-excited character (Figure 4b). The Φ<sub>PL</sub> of **DiKTa3** in degassed toluene is measured to be 0.4%, the magnitude of which is mainly due to the significant non-radiative decay. This low Φ<sub>PL</sub> value is perhaps not

surprising as that of **Hel-DiDiKTa** is also ≈ 1%[¹⁷] and such low Φ<sub>PL</sub> is not uncommon in triple-helicene compounds.[³¹]

The steady-state PL (SS PL) and phosphorescence (Ph) spectra of **DiKTa3** at 77 K were measured in toluene and are shown in Figure 5a–5b. Due to its low Φ<sub>PL</sub>, the SS PL at 77 K is dominated by the phosphorescence. The singlet and triplet energies, determined from the onsets of the SS PL and Ph spectra, are 2.61 and 2.37 eV. The corresponding ΔE<sub>ST</sub> value is 0.24 eV, which is slightly larger than the calculation result (0.14 eV) and similar to that of single **DiKTa** (0.20 eV).[⁴¹] The time-resolved PL decay in degassed toluene is shown in Figure 5c. The prompt emission of **DiKTa3** decays with lifetime τ<sub>PL</sub> of 6.7 ns. No delayed emission was observed in solution because of the low Φ<sub>PL</sub>, large ΔE<sub>ST</sub>, and significant non-radiative decay.[⁴²]

The photophysical properties of **DiKTa3** in doped polymethyl methacrylate (PMMA) films were then investigated. The Φ<sub>PL</sub> remains very low at 0.6% in 1 wt % doped film. **DiKTa3** emits at λ<sub>PL</sub> of 492 nm with FWHM of 54 nm/0.26 eV at 300 K (Figure 6a). The S<sub>1</sub>, T<sub>1</sub> energies and ΔE<sub>ST</sub> value in film, determined from the SS PL and Ph spectra at 77 K, are 2.64, 2.41 eV and

<figure><img src="image_26.png" /><figcaption>**Figure 5.** (a) Steady-state PL and phosphorescence spectra of **DiKTa3** in toluene at 77 K. (b) The fluorescence band of **DiKTa3** in toluene at 77 K. (λ<sub>exc</sub> = 430 nm) (c) Time-resolved PL decay of **DiKTa3** in degassed toluene (λ<sub>exc</sub> = 375 nm).</figcaption></figure>

<figure><img src="image_27.png" /><figcaption>**Figure 6.** (a) Steady-state PL spectra at 300 K (λ<sub>exc</sub> = 415 nm). (b) PL decay of the prompt component at 300 K (λ<sub>exc</sub> = 375 nm). (c) Variable temperature time-resolved PL spectra in 1 wt% doped film in PMMA (λ<sub>exc</sub> = 375 nm).</figcaption></figure>
<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

0.23 eV (Figure S19), which are close to those measured in toluene. The prompt emission decays with a $τ_{PL}$ of 4.0 ns (Figure 6b). There is a weak observed delayed emission, with a lifetime, $τ_d$, of 487 ns (Figure 6c). This delayed emission increases in intensity with increasing temperature, thus we can assign this to TADF.

Recognizing that **DiKTa3** is chiral, we next investigated its chiroptical properties. The enantiomers of the racemic sample of **DiKTa3** were firstly separated by chiral HPLC to afford ee. of 100% and 99.6% for the first and the second enantiomers, respectively (Figure S14–S15). The racemization barrier of **DiKTa3** was firstly calculated at the M062X/6-31G(d,p) level of theory (Figure S20). There are three helical moieties in **DiKTa3**, resulting in three transition states with racemization barriers of $ΔG^‡ = 33.9, 36.8, 33.9 kcal mol⁻¹$ from (P,P,P)- to (P,P,M)-, (P,M,M)- and (M,M,M)-**DiKTa3**, respectively. The calculated high energy barriers enable the chiral separation of **DiKTa3**. The simulated ECD spectra of (P,P,P)-**DiKTa3** in toluene based on PBE0/6-31G(d,p)[30] and M062X/6-31G(d,p)[29] calculations were employed to be able to assign the absolute configuration by comparison with the measured ECD spectra (Figure S21). Both simulated ECD spectra of (P,P,P)-**DiKTa3** show positive signals for the low-energy absorption bands and the M062X/6-31G(d,p) calculations gave simulated spectra that are more consistent with the experimental spectra (Figure 7). (P,P,P)- and (M,M,M)-**DiKTa3** display mirror image ECD spectra. However, the absorption dissymmetry factor $g_{abs}$ values of the lowest-energy absorption band at 450 nm are unexpectedly very low at +6.8×10⁻⁴ and -7.5×10⁻⁴ for (P,P,P)/(M,M,M)-**DiKTa3**, respectively. CPL spectra of (P,P,P)/(M,M,M)-**DiKTa3** in toluene were also measured (Figure S22) with low $g_{PL}$

signals. Due to its weak $Φ_{PL}$, we are not able to extract accurate $g_{PL}$ values.

To explore the origin of the low $g_{abs}$ values, TDA-DFT calculations at the PBE0/6-31G(d,p) and M062X/6-31G(d,p) levels starting from the optimized ground-state geometries of (P,P,P)-**DiKTa3** were firstly performed to predict the $g_{abs}$ values in toluene (Figure 8a–8b). The geometries optimized by both methods are C₃-symmetric triple helicones with the same three torsion angles (C6–C1–N1–C16, C4–C5–N5–C44 and C2–C3–N3–C30) of 38.9, 38.8, 38.8° and 39.4, 39.5, 39.4° for each functional, respectively (Figure S23). They give similar predicted magnetic transition dipole moment values $|**m**|$, small $θ$ of 33 and 3° and high $cosθ$ of 0.84 and 1, respectively. The computed electric transition dipole moment values $|**μ**|$ are higher using M062X/6-31G(d,p), which leads to a lower calculated $g_{abs}$ value of 2.1×10⁻² compared to that of PBE0 (5.6×10⁻¹). However, both predicted values are vastly overestimated compared to the experimental result in toluene. This is likely due to the differences between the near-identical optimized torsion angles and those observed in the single crystal structure (38.4, 35.7 and 42.8°, Figure 2). Therefore, the chiroptical properties of (P,P,P)-**DiKTa3** were also calculated using the crystal structure geometry at the M062X/6-31G(d,p) level for comparison (Figure 8c). The calculated $|**m**|$ is close to the calculations based on the optimized geometries. However, the differences between the three torsion angles breaks the symmetry of the molecule, resulting in an increased $|**μ**|$ and smaller $cosθ$ of 0.38. The corresponding $g_{abs}$ value is calculated to be 8.1×10⁻⁴, which is much closer to the value measured in toluene for the compound (6.8×10⁻⁴). These results indicate

<figure><img src="image_30.png" /><figcaption>**Figure 7.** (a) ECD spectra and (b) $g_{abs}$ values of **DiKTa3** recorded in toluene solution.</figcaption></figure>
<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /><figcaption>**Figure 8.** Density plot of the NTO [hole (blue) & electron (red)] of the S<sub>1</sub> state and calculated chiroptical properties of (P,P,P)-DiKTa3 at the optimized ground-state geometries based on (a) PBE0/6-31G(d,p) and (b) M062X/6-31G(d,p) calculations and (c) at the chiroptical properties at the M062X/6-31G(d,p) level based on the geometry from the crystal structure.</figcaption></figure>

that a slight change in conformation leads to a large
difference in the predicted chiroptical properties.

Conclusions

A new chiral MR-TADF triple helicene **DiKTa3** was designed to have high g<sub>PL</sub> wherein the electronic and magnitude transition dipole moments would align in a co-parallel fashion. The SCS-(ADC)2 calculations and the photophysics point to a compound that is poorly luminescent, although is MR-TADF. The electric and magnetic transition dipole moments of (P,P,P)-**DiKTa3** calculated based on the optimized geometries show almost co-parallel arrangements, which result in large calculated |g<sub>abs</sub>| of > 10<sup>-2</sup>. However, the calculations based on the crystal structure geometry, which adopts a lower symmetry, show much different results where there is an angle of 67° between the electric and magnetic transition dipole moments and a much lower g<sub>abs</sub> of 8.1×10<sup>-4</sup>, a value that aligns with the measured g<sub>abs</sub> of 6.8×10<sup>-4</sup> in toluene. This result illustrates that the geometry of **DiKTa3** in toluene may be closer to that of the crystal structure rather than the perfectly C<sub>3</sub>-symmetric optimized geometries from DFT calculations. This small difference on geometries finally results in large difference in the transition dipole moments and the g value.

**Supporting Information**

¹H and ¹³C NMR spectra, HRMS, HPLC and EA of all target compounds; X-ray crystallographic detail; supplementary computational data; photophysical data.[13,17,29,30,32,33,40,43–70]

Author Contribution Statement

Jingxiang Wang, conceived the molecular design,
performed the synthesis, the theoretical calculations,
and the optoelectronic characterization. The crystal
structures were determined by Dr. Aidan P. McKay and
Dr. David B. Cordes. The chiroptical properties were
measured by Jhon Sebastian Oviedo Ortiz. Dr. Jeanne
Crassous and Prof. Eli Zysman-Colman supervised the
project. All authors contributed to the manuscript.

Acknowledgements

J.W. thanks the China Scholarship Council (202006250026). This project has been partly funded by the European Union Horizon 2021 research and innovation programme under grant agreement No. 101073045 (TADF solutions) and the EPSRC grant EP/ X026175/1 . J.C. acknowledge the Ministère de l'Enseignement Supérieur et de la Recherche and the Centre National de la Recherche Scientifique (CNRS).
<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>

The St Andrews team acknowledges the Engineering and Physical Sciences Research Council of the UK for support through grants EP/P010482/1 and EP/W007517/1).

## Conflict of Interest

The authors declare no conflict of interest.

## Data Availability Statement

The research data supporting this publication can be accessed at https://doi.org/10.17630/a3917a0d-9839-4465-8c51-f89d4a0fd44d. Deposition Number https://www.ccdc.cam.ac.uk/services/structures?id=doi:10.1002/hlca. 202400129, CCDC 2376257 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.

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Received September 4, 2024

Accepted October 14, 2024