Rational design of star-shaped triarylborane-based thermally activated delayed fluorescent emitters for organic light-emitting diodes

doi:10.21203/rs.3.rs-3230300/v1

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Rational design of star-shaped triarylborane-based thermally activated delayed fluorescent emitters for organic light-emitting diodes

https://doi.org/10.21203/rs.3.rs-3230300/v1

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A series of novel donor (D)–acceptor (A) star-shaped triarylborane-based molecules have been designed for the applications in organic light-emitting diodes (OLEDs) devices with thermally activated delayed fluorescence (TADF) properties. Their photophysical and electronic properties have been systematically investigated by applying density functional theory (DFT) and time dependent DFT (TD-DFT) methods. The frontier molecular orbitals (FMOs) analysis has turned out that the vertical electronic transitions exhibit a strong charge transfer character. The D and A fragments are separated efficiently. Furthermore, all the designed molecules display small singlet-triplet energy gap (ΔE_ST) values, which is beneficial for TADF properties. Our results suggest that the introduction of different donors can tune the delayed fluorescence emission colour effectively. The designed molecules are expected to be the promising candidates TADF materials for organic light-emitting diodes (OLEDs).

Thermally activated delayed fluorescence (TADF)

Singlet-triplet energy gap

Optical and electronic properties

Reverse intersystem crossing (RISC)

Organic light-emitting diodes (OLEDs)

Thermally activated delayed fluorescence (TADF) materials have recently aroused a lot of interest as promising emitters in organic light-emitting diodes (OLEDs) due to their theoretical maximum internal quantum efficiency (IQE) and low cost [1–6]. Having efficient reverse intersystem crossing (RISC) from the lowest triplet excited state (T₁) to the lowest singlet excited state (S₁), TADF materials can harvest both singlet and triplet excitons without employing any noble metals and can therefore reach 100% of IQE [7–9]. With the aim of efficient RISC process, a small energy gap (ΔE_ST) between the S₁ and T₁ states is an essential requirement, which should be lower than 0.3 eV [10–12]. Accordingly, in order to obtain a small ΔE_ST, an effective strategy for designing TADF materials is separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which facilitates a small ΔE_ST [13, 14]. Generally, efficient TADF materials adopt a highly twisted charge-transfer (CT) electron-donor (D)–electron-acceptor (A) conformations to break the conjugation between D and A moieties [15–17]. Such frameworks can lead to a small overlap between the HOMO and LUMO, which is favorable for a small ΔE_ST. As a consequence, these designed TADF materials exhibit efficient RISC process [18–20]. Additionally, it is noteworthy that the selection and synthesis of the D and A units are important for achieving ideal TADF materials, because their structures determine the S₁ and T₁ states energies, HOMO and LUMO energies, and ΔE_ST for designed materials, which are related to the device emission characteristics [21]. At the same time, star-shaped conjugated D–A materials exhibit good charge transport property because no an ordered, long-range, and coplanar π-π stacking are formed owing to their steric hindrance [22]. Furthermore, the photophysical properties can be tuned effectively by adjusting the core and arm fragments of star-shaped D–A materials [23]. According to this basic design principle, many TADF materials have been developed with a wide range of emission colors. Abundant TADF materials with amine based D segments exhibit good TADF properties [24, 25]. In addition, TADF materials with different A moieties such as benzonitrile, triazines, sulfones, benzophenone, quinoxaline and naphthalimide possess excellent electroluminescence performance [26–31]. Among the numerous reported TADF materials, boron-containing π-conjugated systems have received considerable attention recently owing to their superior TADF characteristics [32, 33]. The central boron atom in D–A molecule has a vacant p orbital and exhibit electron-deficient nature through p-π conjugations, which facilitate the ICT [34, 35]. As a consequence, boron-containing molecules display unique optoelectronic functions and greatly enhance OLEDs performance [36, 37]. Furthermore, the performances of TADF emitters can managed by the substituent and substitution position of the A and D units because they influence the conjugation, ΔE_ST, and distortion of A and D moieties [38, 39]. However, there still exist some challenges in designing and synthesizing ideal TADF materials, such as the relationship between topologic structure of D or A units and TADF properties. It is therefore necessary to design new TADF materials, providing a demonstration for the rational design of a novel candidate for TADF materials for OLEDs.

In this work, we designed a series of novel triarylborane-based TADF molecules. As shown in Scheme 1, these molecules consist of the boronate-thioester 5,9-dioxa-13b-boranaphtho[3 ,2,1-de]anthracene (DBNA) fragments as A units and different polycyclic aromatics fragments as D units for TADF molecules. In order to tune the emitting colour, eight substituent are introduced at different positions of A units by changing the π-conjugation degree on A units. We have investigated the TADF properties of the designed molecules by calculating the frontier molecular orbitals (FMOs) energies (E_HOMO and E_LUMO), the HOMO-LUMO gaps (E_g), and ΔE_ST using density functional theory (DFT) and time dependent DFT (TD-DFT). Their absorption, fluorescence, and phosphorescence spectra were predicted by mean of TD-DFT method.

(Insert Scheme. 1.)

The geometric and electronic structures for the designed molecules in the S₀ states in the gas phase were investigated using DFT method in the Gaussian 09 package [40]. The corresponding frequency analysis characterizes that the optimized structures are true minima on the potential energy surface. The TD-DFT was adopted to optimize the S₁ and T₁ state geometries. The Mulliken population analysis, the overlap value (ρ) between D and A fragments on FMOs, and the contributions (%) from D and A fragments to the FMOs are calculated at the current level of theory using Pymolyze 2.0 [41]. The ΔE_ST values were evaluated by the adiabatic excitation energy method. The absorption and emission spectra were predicted using the TD-DFT method based on the S₀, S₁, and T₁ optimized structures, respectively. The 6-31G (d,p) basis set was selected for all the calculations. However, the TADF molecules have a strong charge transfer character. In some case, the unphysical long-range asymptote of the exchange part of the traditional DFT and TD-DFT makes them unsuitable for calculations of excited states having a large charge-transfer (CT) component and triplet states [42–44]. In order to select reasonable approach, we take 7-(10H-phenoxazin-10-yl)-5,9-dioxa13b-branaphtho[3,2,1-de]anthracene (PODBNA) as an example because its geometric structure is similar to our system. Various functional such as B3LYP [45], PBE0 [46], PBEPBE [47], ωB97XD [48], M062X [49], and CAM-B3LYP [50] were employed to optimize the geometries of PODBNA in S₀, S₁, and T₁ states by mean of DFT and TD-DFT methods, respectively. The absorption, fluorescence and phosphorescence spectra were predicted based on the S₀, S₁, and T₁ states optimized structures. The predicted ΔE_ST values, absorption (λ_abs), fluorescence emission (λ_fl), phosphorescence emission (λ_ph) wavelengths as well as the experimental data are given in Table SI in Supporting Information. The predicted λ_fl values using various functional, together with the experimental results are shown in Fig. 1. Apparently, the λ_fl value obtained at the PBEPBE theoretical level (494 nm) is quite close to the experimental value (492 nm) [51], with the deviation of 2 nm. Additionally, calculated ΔE_ST value obtained at the PBEPBE method (0.2068 eV) is smaller than that TADF materials (> 0.3 eV) and is close to the experimental value (0.006 eV), with the deviation of 0.1468 eV. The calculated ΔE_ST value is smaller than that TADF material. In addition, the reports in the literature suggested that the traditional DFT and TD-DFT appeared notably adapted to the TADF molecules [52–56]. Furthermore, it is well known that the ISC and RISC rates are not only relevant to ∆E_ST but also proportional to the square of the spin-orbital coupling (SOC) between selected singlet and triplet states. Though SOC can be estimated [57, 58], we cannot predict them for our designed molecules by similar methods due to the lack of available programs such as ADF. We plan to investigate this in future work. Thus, we focused on their ∆E_ST, the fluorescence and phosphorescent key parameters to investigate their TADF properties [59, 60]. Accordingly, geometry optimizations in S₀, S₁, and T₁ states, band gaps E_g, ΔE_ST, absorption and emission spectra of the designed molecules were carried out by the PBEPBE/6-31G(d,p) and TD-PBEPBE/6-31G(d,p) methods.

(Insert Fig. 1)

3.1 Geometry optimization in S₀, S₁, and T₁ states

The important inter-ring bond lengths and distortion angles of 1–8 in S₀, S₁, and T₁ states are given in Table SII in Supporting Information. From Table SII one can find that there are no significant changes on the bond lengths of acceptors DBNA fragments for 1–8 in S₀ states. The main bond lengths alteration appeared on the bonds those connect the acceptor DBNA and different donor fragments (The atom numbering of the designed molecules see Fig. SI in Supporting Information). The inter-ring distances A–D of 1–8 are 1.417, 1.416, 1.423, 1.423, 1.419, 1.422, 1.420, and 1.421 Å, respectively. It has also been noted that 1–8 possess large distortion angles between their A and D units in the S₀ owing to their large steric hindrance. The smallest distortion angles values of 1–8 are 93.4˚, 101.6˚, 80.0˚, 85.5˚, 78.9˚, 78.0˚, 89.3˚, and 79.9˚, respectively. The large distortion angles values are favorable for the disrupting the electronic communication between D and A fragments. In the S₁ state, the bond lengths of B₁–C₆, B₁–C₇, C₅–C₁₉, C₈–C₂₅, C₁₀–C₁₁, C₁₇–C₁₈, C₂₃–C₂₄ for 1–8 are shortened compared to those in the S₀ states, respectively. Meanwhile, the bond lengths of B₁–C₂ for 1, 2, 5, and 6, C₂–C₃ and C₂–C₁₀ for 3, 4, and 8, C₃–C₁₃ for 1, 2, 5, 6, 7, and 8 are decreased compared to those in the S₀ states, respectively. Other bond lengths of DBNA fragments for the designed molecules in S₁ states are enlarged with respect to those in the S₀ states, respectively. Furthermore, the distortion angles between their A and D fragments are more close to 90˚ in the S₁ state as compared to those in the S₀ states for 1–8. As a consequence, the steric separation of the FMO is taken place easily. Moreover, the differences in the distortion angles between S₀ and S₁ for 1–8 are small. Accordingly, the non-radiative decay from S₁ to S₀ can be subdued efficiently [61, 62]. At the same time, the results displayed in Table SII in Supporting Information reveal that the inter-ring bond lengths and distortion angles in T₁ states are similar to those in S₁ states for 1–8, respectively. It is expected that up-conversion from triplet to singlet exciton might be more efficiently.

3.2 Frontier molecular orbital level and band gaps

With the aim to explore the optical and electronic properties, it is important to examine the character of FMOs. The electronic density contours of HOMO and LUMO in S₀ states are depicted in Fig. 2. At the same time, we also investigated the percentage of electronic distribution on the FMOs and the overlap value (ρ) between D and A fragments on HOMOs and LUMOs, as displayed in Table 1. In the S₀ state, both the HOMOs and LUMOs of 1–8 possessed exhibited π orbital features, as visualized in Fig. 2. The results displayed in Table 1 reveal that the HOMOs of 1–8 are predominantly distributed on the D fragments, whereas the LUMOs mainly localized on A fragments. The contributions of D fragments for HOMOs are larger than 96.9%, whereas the corresponding contributions of A fragments are smaller than 3.1%, respectively. For the LUMOs, the contributions of A fragments in 1–8 are larger than 95.9%, while the corresponding contributions are smaller than 4.1%. Accordingly, the HOMOs to LUMOs transitions have a strong charge transfer character. Especially, the overlap ρ values for HOMOs are in the range of 0.013–0.020, while the corresponding ρ values for LUMOs are 0.021–0.027. It also confirms that the strong charge transfer nature and exhibits a small electron exchange energy, which led to a ΔE_ST values.

Table 2 collected the E_HOMO, E_LUMO, E_g, the percentage of electronic distribution on the FMOs, and the overlap value (ρ) between D and A fragments on HOMOs and LUMOs of the investigated molecules in the S₁ states. The distribution patterns and energy levels of the HOMOs and LUMOs of 1–8 in the S₁ state are shown in Fig. 3. Inspection of Fig. 3 reveals clearly that HOMOs and LUMOs are also separated efficiently in the S₁ state as those in S₀ states for the designed molecules [63, 64]. The HOMOs and LUMOs are mostly located on the D and A fragments, respectively. The results displayed in Table 2 show that the contributions of D fragments for HOMOs are larger than 97.9%, whereas the contributions of A fragments for the LUMOs are larger than 97.3%. Remarkably, the HOMOs to LUMOs transitions possess stronger charge transfer feature than that in S₀ states. Furthermore, it can be noted that the ρ values for HOMOs and LUMOs are in the ranges of 0.009–0.014 and 0.019–0.028, respectively. It indicates that D and A fragments are separated efficiently in the S₁ state, which is beneficial for the TADF properties. The E_HOMO values are in the order of 5 > 3 > 1 > 6 > 4 > 8 > 2 > 7 while the E_LUMO values are in the sequence of 5 > 6 > 8 > 1 > 3 > 7 > 4 > 2. It is noted that both HOMOs and LUMOs values of 2, 4, and 7 are decreased compared with those of 1, 3, and 6, respectively. It indicates that the “CH”/N substitution can decrease the FMOs energy levels. The HOMOs and LUMOs values of 8 are lower than those of 6, respectively. It implies that the enhancement of the electron donating ability of the donors results in lower FMOs energy levels. The E_g values are in the order of 8 > 6 > 7 > 2 > 1 > 3 > 4 > 5. It can be found that the E_g values of 3–5 decrease, whereas the E_g values of 2, 6–8 increases compared with that of 1. Therefore, one can anticipate that red shift emissions for 3–5 and blue shift emissions for 2, 6–8 could be observed compared with that for 1. As mentioned above, one can conclude that the introduction of different end-capper D fragments can tune effectively the FMOs energy levels for the designed molecules. In addition, we also investigated the character of FMOs in T₁ states. (Fig. SII). As expect, the electronic density contours of HOMOs and LUMOs in T₁ states are similar to those in S₁ states, respectively. It is facilitate for the RISC process from T₁ to S₁ states.

Table 1

The HOMO and LUMO Contributions (%) and the overlap between D and A fragments on HOMOs and LUMOs (ρ) of 1–8 in S₀ states at the PBEPBE/6-31G(d,p) level.
Species	HOMO			LUMO
Species	A^a	D^b	ρ	A	D	ρ
1	2.5	97.5	0.017	96.9	3.1	0.024
2	3.1	96.9	0.020	95.9	4.1	0.023
3	1.8	98.2	0.014	96.6	3.4	0.021
4	1.6	98.4	0.013	96.5	3.5	0.022
5	1.7	98.3	0.013	97.2	2.8	0.026
6	2.5	97.5	0.018	97.2	2.8	0.027
7	2.6	97.4	0.017	97.2	2.8	0.026
8	2.6	97.4	0.020	97.1	2.9	0.023
^a A: boronate-thioester 5,9-dioxa-13b-boranaphtho[3 ,2,1-de]anthracene (DBNA) fragments. ^b D: different polycyclic aromatics fragments.

Table 2

The FMOs energies E_HOMO and E_LUMO, HOMO–LUMO gaps E_g (all in eV), HOMOs and LUMOs contributions (%) and the overlap (ρ) between D and A fragments on HOMOs and LUMOs of 1–8 in S₁ states.
Species	HOMO				LUMO				E_g
Species	E_HOMO	A^a	D^b	ρ	E_LUMO	A	D	ρ	E_g
1	-5.193	1.8	98.2	0.013	-2.082	97.3	2.7	0.022	3.111
2	-5.745	1.8	98.2	0.014	-2.591	97.3	2.7	0.019	3.154
3	-5.139	1.4	98.6	0.009	-2.100	97.0	3.0	0.025	3.040
4	-5.609	1.3	98.7	0.009	-2.588	96.9	3.1	0.024	3.020
5	-4.557	1.4	98.6	0.010	-1.858	97.3	2.7	0.025	2.699
6	-5.480	2.1	97.9	0.012	-1.895	97.3	2.7	0.028	3.585
7	-5.921	2.1	97.9	0.013	-2.345	97.3	2.7	0.026	3.576
8	-5.620	2.2	97.9	0.013	-1.915	97.3	2.7	0.025	3.706
^a A: boronate-thioester 5,9-dioxa-13b-boranaphtho[3 ,2,1-de]anthracene (DBNA) fragments. ^b D: different polycyclic aromatics fragments.

(Insert Table 1)

(Insert Table 2)

(Insert Fig. 2)

(Insert Fig. 3)

3.3 Singlet-triplet energy gap

The calculated singlet and triplet vertical excitation energy (E_S1 and E_T1) and ΔE_ST of 1–8 are listed in Table 3. It is worth noting that smaller ΔE_ST is favorable for RISC process from the T₁ to S₁ states [11, 12]. The results displayed in Table 3 show that the calculated E_S1 values of 1–8 decreases in the order of 8 > 6 > 7 > 2 > 1 > 3 > 4 > 5, which is consistent with the order of E_g values in S₁ states (see Table 2). However, the calculated E_T1 values of 1–8 are in the sequence of 6 > 7 > 8 > 2 > 1 > 4 > 3 > 5. Obviously, the designed molecules exhibit small ΔE_ST values (0.0070–0.1891 eV). Molecules 5 and 8 own the smallest and largest ΔE_ST values among the designed molecules, respectively. The predicted ΔE_ST values of 1–8 are lower than 0.3 eV [10]. Therefore, the efficient RISC process may take place because of their small ΔE_ST values for the designed molecules. The predicted ΔE_ST values is in the sequence 8 (0.1891) > 3 (0.0904) > 4 (0.0651) > 7 (0.0456) > 6 (0.0267) > 2 (0.0088) > 1 (0.0086) > 5 (0.0070). It is noted that the ΔE_ST values of 2, 4, and 7 are close to those of 1, 3, and 6, respectively. It indicates that the “CH”/N substitution does not significantly affect the ΔE_ST values compared with the parent molecules. As mentioned above, the HOMOs to LUMOs transitions have a strong charge transfer character in S₁ state. The contributions of D and A fragments for HOMOs and LUMOs are larger than 97.9% and 97.3%, respectively. Furthermore, the ρ values for HOMOs and LUMOs are in the ranges of 0.009–0.014 and 0.019–0.028, respectively. It indicates that D and A fragments are separated efficiently in the S₁ state, which is beneficial for the TADF properties. Additionally, the distortion angles between their A and D fragments are more close to 90˚ in the S₁ state as compared to those in the S₀ states. Therefore, the steric separation of the HOMOs and LUMOs is taken place easily. The designed molecules may exhibit high RISC rate constant (k_RISC) because a small ΔE_ST value is beneficial for the high k_RISC value. As a consequence, the designed molecules exhibit TADF property.

Table 3

Calculated vertical excitation energy of S₁ and T₁ (E_S1 and E_T1) and singlet-triplet energy gap (ΔE_ST) of 1–8 at the TD-PBEPBE/6-31G(d,p) level (in eV).
Species	E_S1	E_T1	ΔE_ST
1	2.2586	2.2518	0.0086
2	2.3019	2.2981	0.0088
3	2.2018	1.9776	0.0904
4	2.1866	1.9783	0.0651
5	1.8803	1.8744	0.0070
6	2.7011	2.6455	0.0267
7	2.7004	2.6327	0.0456
8	2.7724	2.4605	0.1891

(Insert Table 3)

3.4 Photophysical properties

As mentioned above, the designed molecules exhibit TADF property, thus, the predicted fluorescence emissions are the delayed fluorescence emissions. Table 4 collected the wavelength of delayed fluorescence emission (λ_TADF), phosphorrescence emission (λ_ph), absorption (λ_abs), and Stokes shift of the designed molecules. From Table 4, one can be noted that the λ_abs values of the designed molecules have hypsochromic shifts compared with that of molecule 1, respectively, except that the corresponding value of 5 shows bathochromic shift compared with that of molecule 1. As shown in Fig. 3, the delayed fluorescent band for the designed molecules can be assigned to the LUMOs → HOMOs transitions, which corresponds to π-π* transitions. Meanwhile, as expect, the tendency of the singlet vertical excitation energy (E_S1) is consistent with the order of E_g values in S₁ states (see Table 1). It can be noted that the λ_TADF values of 1–8 are in the sequence of 5 > 4 > 3 > 1 > 2 > 7 > 6 > 8, which is similar to the corresponding reverse order of their E_g and E_S1 values. The results displayed in Table 4 show that the λ_TADF values of 2 and 6–8 exhibit hypsochromic shifts, 10, 90, 88, and 102 nm compared with that of 1, respectively. On the contrary, the λ_TADF values of 3–5 have bathochromic shifts, 14, 18, and 110 nm compared with that of 1, respectively. It is interesting to note that 3–5 display more significant Stokes shifts (141, 102, and 130 nm). Molecules 3 and 4 exhibit turquoise emissions and molecule 5 shows red emission with small ΔE_ST values. On the other hand, molecules 1, 2, and 6–8 have small Stokes shifts 75, 76, 60, 38, and 54 nm, respectively. Additionally, molecules 6 and 7 possess bright blue emissions, whereas 1, 2, and 8 exhibit bright green, green, and dark blue emissions, respectively. Therefore, one can conclude that the introduction of different end-capper fragments as electron donors can tune the delayed fluorescence emission color effectively. Our results suggest that the designed molecules can serve as promising TADF materials for OLEDs. We also calculated the λ_ph values of the designed molecules. Comparing the λ_ph values with the λ_TADF values, one can find that the λ_ph values are similar to the λ_TADF values, which should favourable for achieving the TADF feature.

Table 4

Calculated absorption (λ_abs), delayed fluorescence emission (λ_TADF), phosphorescence emission (λ_ph) wavelengths, and Stokes shifts (all in nm) of 1–8 at the TD-PBEPBE/6-31G (d,p) level.
Species	λ_abs	λ_TADF	λ_ph	Stokes shift
1	474	549	551	75
2	463	539	540	76
3	422	563	627	141
4	465	567	627	102
5	529	659	662	130
6	399	459	469	60
7	423	461	471	38
8	393	447	504	54

(Insert Table 4)

In the present work, we design a series of novel D–A star-shaped molecules with 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DBNA) fragments as core and different polycyclic aromatics fragments as end groups for thermally activated delayed fluorescence (TADF) materials. Their photophysical and electronic properties have been systematically investigated by applying DFT and TD-DFT methods. The FMOs analysis shows that the vertical electronic transitions exhibit a strong charge transfer character. The D and A fragments are separated efficiently because the HOMOs and LUMOs are mostly located on the D and A fragments with small overlap between D and A fragments (ρ) on HOMOs and LUMOs, respectively. Furthermore, all the designed molecules display small ΔE_ST values, which is beneficial for TADF properties. Our results suggest that the introduction of different donors can tune the delayed fluorescence emission colour effectively. Molecules 3 and 4 exhibit turquoise emissions and molecule 5 shows red emission with large Stokes shifts (141, 102, and 130 nm). On the other hand, other molecules possess bright green (1), green (2), bright blue (6, 7), and dark blue (8) emissions. Therefore, the designed molecules are expected to be the promising candidates TADF materials for OLEDs.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No.21563002); the Natural Science Foundation of Inner Mongolia Autonomous Region (Grant No. 2021LHMS02001); and the Research Program of Sciences at Universities of Inner Mongolia Autonomous Region (Grant No. NJSY21124).

Author contribution

RJ: Conceptualization, design, Supervision, Formal analysis, writing—original draft, and project administration. JX: Data curation, Supporting methodology, Validation, and Methodology. WX: data collection, and Visualization. All authors have read and agreed to the published version of the manuscript.

Competing interests

The authors declare that they have no competing interests.

Supplementary Information

The online version contains supplementary material available at https:// doi. org/ 10.

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Scheme 1 is available in the Supplementary Files section

No competing interests reported.

Scheme1.png
Scheme. 1. Geometries of the designed molecules
supportinginformation.doc
GA.png
A series of novel D–π–A triarylborane-based molecules with TADF propertiesis investigated. The vertical electronic transitions exhibit a strong charge transfer character. The designed molecules display smallsinglet-triplet energy gap values. The introduction of different donorscan tune the delayed fluorescence emission color effectively. The results suggest that the designed moleculesare promising candidates TADF materials for OLEDs.

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Rational design of star-shaped triarylborane-based thermally activated delayed fluorescent emitters for organic light-emitting diodes

Status:

Version 1

Abstract

Figures

1. Introduction

2. Computational Methods

3. Results and discussion

3.1 Geometry optimization in S₀, S₁, and T₁ states

3.2 Frontier molecular orbital level and band gaps

3.3 Singlet-triplet energy gap

3.4 Photophysical properties

4. Conclusions

Declarations

References

Schemes

Additional Declarations

Supplementary Files

Status:

Version 1

Species	λ_abs	λ_TADF	λ_ph	Stokes shift
1	474	549	551	75
2	463	539	540	76
3	422	563	627	141
4	465	567	627	102
5	529	659	662	130
6	399	459	469	60
7	423	461	471	38
8	393	447	504	54

Species	λ_abs	λ_TADF	λ_ph	Stokes shift
1	474	549	551	75
2	463	539	540	76
3	422	563	627	141
4	465	567	627	102
5	529	659	662	130
6	399	459	469	60
7	423	461	471	38
8	393	447	504	54

Rational design of star-shaped triarylborane-based thermally activated delayed fluorescent emitters for organic light-emitting diodes

Status:

Version 1

Abstract

Figures

1. Introduction

2. Computational Methods

3. Results and discussion

3.1 Geometry optimization in S0, S1, and T1 states

3.2 Frontier molecular orbital level and band gaps

3.3 Singlet-triplet energy gap

3.4 Photophysical properties

4. Conclusions

Declarations

References

Schemes

Additional Declarations

Supplementary Files

Status:

Version 1

3.1 Geometry optimization in S₀, S₁, and T₁ states

Species	λ_abs	λ_TADF	λ_ph	Stokes shift
1	474	549	551	75
2	463	539	540	76
3	422	563	627	141
4	465	567	627	102
5	529	659	662	130
6	399	459	469	60
7	423	461	471	38
8	393	447	504	54