TY - JOUR
T1 - Benzo[1,2-b:4,5-b']dithiophene as a weak donor component for push-pull materials displaying thermally activated delayed fluorescence or room temperature phosphorescence
AU - Cardeynaels, Tom
AU - Paredis, Simon
AU - Danos, Andrew
AU - Vanderzande, Dirk
AU - Monkman, Andrew P.
AU - Champagne, Benoît
AU - Maes, Wouter
N1 - Funding Information:
The novel BDT-TIPS donor building block was synthesized as a boronic ester according to literature, as shown in Scheme 1 [48]. Triisopropylsilyl (TIPS) protection is necessary to prevent boroester formation on the thienyl 2- and 3-positions. Coupling to different acceptors was achieved using Suzuki-Miyaura cross-coupling, while Buchwald-Hartwig cross-coupling was used for the DMAC compounds. Full details of all synthetic procedures are included in the supporting information (SI).For TXO2-BDT-TIPS, it is possible that the observed RTP is coming from localized emission corresponding to the BDT-TIPS unit (Fig. 4). When looking at the pure BDT-TIPS and TXO2-BDT-TIPS spectra at room temperature and at 80 K, the similarities in the peak shape and onset indicates that emission is coming from similar states in both materials. The difference in onset could be due to the acceptor properties of TXO2, slightly lowering the BDT triplet energy level in the D-A-D compound, or from the vibrational mode of the highest energy vibronic peak in the BDT-TIPS phosphorescence spectrum being suppressed in the D-A-D material. Furthermore, the ground‒excited state electron density differences predict the T1 and T2 states to be localized on the BDT-TIPS group (Fig. S9). CNQxP-BDT-TIPS behaves differently, as microsecond emission (attributed to TADF) is also observed. The large difference in the onset of the emission at several milliseconds at room temperature and at 80 K allows us to exclude RTP for this compound. One of the reasons is that the CT triplet of the D-A-D compound has a lower energy than the localized BDT-TIPS triplet state and coupling to the ground state from the CT triplet state is inefficient. Alternatively, rISC could be competing with the radiative relaxation from the T1 state due to the smaller ΔEST with respect to TXO2-BDT-TIPS and the improved SOC. The ground‒excited state electron density differences (Fig. S10) show significant CT character for the lowest excited triplet state, supporting this hypothesis.This work is supported by the University of Namur and Hasselt University [PhD BILA scholarship T. Cardeynaels]. The authors also thank the Research Foundation – Flanders (FWO Vlaanderen) for financial support [project G.0877.18 N, Hercules project GOH3816NAUHL, and SB PhD scholarship S. Paredis]. The calculations were performed on the computers of the « Consortium des équipements de Calcul Intensif (CÉCI) » (http://www.ceci-hpc.be), including those of the « UNamur Technological Platform of High-Performance Computing (PTCI) » (http://www.ptci.unamur.be), for which we gratefully acknowledge the financial support from the FNRS-FRFC, the Walloon Region, and the University of Namur [Conventions No. 2.5020.11, GEQ U.G006.15, U.G018.19, 1610468, and RW/GEQ2016]. A. Danos and A.P. Monkman are supported by EU Horizon 2020 Grant Agreement No. 732013 (HyperOLED). We thank Alastair Harrison for assistance in collecting spectroscopic data for TXO2-DMAC.
Funding Information:
This work is supported by the University of Namur and Hasselt University [PhD BILA scholarship T. Cardeynaels]. The authors also thank the Research Foundation – Flanders (FWO Vlaanderen) for financial support [project G.0877.18 N, Hercules project GOH3816NAUHL, and SB PhD scholarship S. Paredis]. The calculations were performed on the computers of the « Consortium des équipements de Calcul Intensif (CÉCI) » ( http://www.ceci-hpc.be ), including those of the « UNamur Technological Platform of High-Performance Computing (PTCI) » ( http://www.ptci.unamur.be ), for which we gratefully acknowledge the financial support from the FNRS-FRFC, the Walloon Region , and the University of Namur [Conventions No. 2.5020.11, GEQ U.G006.15, U.G018.19, 1610468, and RW/GEQ2016]. A. Danos and A.P. Monkman are supported by EU Horizon 2020 Grant Agreement No. 732013 (HyperOLED). We thank Alastair Harrison for assistance in collecting spectroscopic data for TXO2-DMAC.
Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2021/2
Y1 - 2021/2
N2 - In the search for high-performance donor-acceptor type organic compounds displaying thermally activated delayed fluorescence (TADF), triisopropylsilyl-protected benzo[1,2-b:4,5-b']dithiophene (BDT-TIPS) is presented as a novel donor component in combination with two known acceptors: dimethyl-9H-thioxanthenedioxide (TXO2) and dibenzo[a,c]phenazinedicarbonitrile (CNQxP). For a broader comparison, the same acceptors are also combined with the well-studied 9,9-dimethyl-9,10-dihydroacridine (DMAC) donor. Optimized BDT-TIPS-containing structures show calculated dihedral angles of around 50° and well-separated highest occupied and lowest unoccupied molecular orbitals, although varying singlet-triplet energy gaps are observed experimentally. By changing the acceptor moiety and the resulting ordering of excited states, room temperature phosphorescence (RTP) attributed to localized BDT-TIPS emission is observed for TXO2-BDT-TIPS, whereas CNQxP-BDT-TIPS affords a combination of TADF and triplet-triplet annihilation (TTA) delayed emission. In contrast, strong and pure TADF is well-known for TXO2-DMAC, whereas CNQxP-DMAC shows a mixture of TADF and TTA at very long timescales. Overall, BDT-TIPS represents an alternative low-strength donor component for push-pull type TADF emitters that is also able to induce RTP properties.
AB - In the search for high-performance donor-acceptor type organic compounds displaying thermally activated delayed fluorescence (TADF), triisopropylsilyl-protected benzo[1,2-b:4,5-b']dithiophene (BDT-TIPS) is presented as a novel donor component in combination with two known acceptors: dimethyl-9H-thioxanthenedioxide (TXO2) and dibenzo[a,c]phenazinedicarbonitrile (CNQxP). For a broader comparison, the same acceptors are also combined with the well-studied 9,9-dimethyl-9,10-dihydroacridine (DMAC) donor. Optimized BDT-TIPS-containing structures show calculated dihedral angles of around 50° and well-separated highest occupied and lowest unoccupied molecular orbitals, although varying singlet-triplet energy gaps are observed experimentally. By changing the acceptor moiety and the resulting ordering of excited states, room temperature phosphorescence (RTP) attributed to localized BDT-TIPS emission is observed for TXO2-BDT-TIPS, whereas CNQxP-BDT-TIPS affords a combination of TADF and triplet-triplet annihilation (TTA) delayed emission. In contrast, strong and pure TADF is well-known for TXO2-DMAC, whereas CNQxP-DMAC shows a mixture of TADF and TTA at very long timescales. Overall, BDT-TIPS represents an alternative low-strength donor component for push-pull type TADF emitters that is also able to induce RTP properties.
KW - Benzo[1,2-b:4,5-b']dithiophene
KW - Organic light-emitting diodes
KW - Photophysical and quantum-chemical characterizations
KW - Room temperature phosphorescence
KW - Thermally activated delayed fluorescence
UR - http://www.scopus.com/inward/record.url?scp=85097450889&partnerID=8YFLogxK
U2 - 10.1016/j.dyepig.2020.109022
DO - 10.1016/j.dyepig.2020.109022
M3 - Article
AN - SCOPUS:85097450889
VL - 186
JO - Dyes and pigments
JF - Dyes and pigments
SN - 0143-7208
M1 - 109022
ER -