Emission wavelength dependence on the rISC rate in TADF compounds with large conformational disorder

Serevičius, Tomas; Skaisgiris, Rokas; Dodonova, Jelena; Jagintavičius, Laimis; Bucevičius, Jonas; Kazlauskas, Karolis; Juršėnas, Saulius; Tumkevičius, Sigitas

doi:10.1039/c8cc08906j

Cited by 34 publications

(33 citation statements)

References 23 publications

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“…Prompt fluorescence decay transients of 10 wt % DPEPO films of compounds PXZ-PYR , PXZ-muPYR , PXZ-mdPYR , and PXZ-2mPYR in the −O 2 surrounding (see Figure 4 b) were similar to toluene solutions; however, the TADF decay was strongly multiexponential for compounds PXZ-muPYR , PXZ-mdPYR , and PXZ-2mPYR due to the presence of conformational disorder (see Figure S31 in the Supporting Information for time-resolved spectra, showing temporal shifts of the emission peak). 37 , 52 , 56 − 61 Although no exact TADF lifetime and decay rates could be estimated, still the slowest TADF decay could be attributed for PXZ-2mPYR . On the contrary, an approximate three-exponential fit of fluorescence decay transient was successfully applied for PXZ-muPYR with the most rapid rISC in toluene, 37 though the latest DF decay tail (from about 10 –5 to about 10 –4 s) still was impossible to fit.…”

Section: Resultsmentioning

confidence: 99%

“… 37 , 52 , 56 − 61 Although no exact TADF lifetime and decay rates could be estimated, still the slowest TADF decay could be attributed for PXZ-2mPYR . On the contrary, an approximate three-exponential fit of fluorescence decay transient was successfully applied for PXZ-muPYR with the most rapid rISC in toluene, 37 though the latest DF decay tail (from about 10 –5 to about 10 –4 s) still was impossible to fit. Roughly, a solid-state TADF lifetime of only 860 ns was obtained, being one of the lowest among the ever reported for various TADF compounds 7 , 21 , 51 , 62 and especially for pyrimidine derivatives (see Table S2 in the Supporting Information ).…”

Section: Resultsmentioning

confidence: 99%

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Achieving Submicrosecond Thermally Activated Delayed Fluorescence Lifetime and Highly Efficient Electroluminescence by Fine-Tuning of the Phenoxazine–Pyrimidine Structure

Serevičius

Skaisgiris

Dodonova

et al. 2020

ACS Appl. Mater. Interfaces

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Thermally activated delayed fluorescence (TADF) materials, combining high fluorescence quantum efficiency and short delayed emission lifetime, are highly desirable for application in organic light-emitting diodes (OLEDs) with negligible external quantum efficiency (EQE) roll-off. Here, we present the pathway for shortening the TADF lifetime of highly emissive 4,6-bis[4-(10-phenoxazinyl)phenyl]pyrimidine derivatives. Tiny manipulation of the molecular structure with methyl groups was applied to tune the singlet–triplet energy-level scheme and the corresponding coupling strengths, enabling the boost of the reverse intersystem crossing (rISC) rate (from 0.7 to 6.5) × 10 6 s –1 and shorten the TADF lifetime down to only 800 ns in toluene solutions. An almost identical TADF lifetime of roughly 860 ns was attained also in solid films for the compound with the most rapid TADF decay in toluene despite the presence of inevitable conformational disorder. Concomitantly, the boost of fluorescence quantum efficiency to near unity was achieved in solid films due to the weakened nonradiative decay. Exceptional EQE peak values of 26.3–29.1% together with adjustable emission wavelength in the range of 502–536 nm were achieved in TADF OLEDs. Reduction of EQE roll-off was demonstrated by lowering the TADF lifetime.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Achieving Submicrosecond Thermally Activated Delayed Fluorescence Lifetime and Highly Efficient Electroluminescence by Fine-Tuning of the Phenoxazine–Pyrimidine Structure

Serevičius

Skaisgiris

Dodonova

et al. 2020

ACS Appl. Mater. Interfaces

Self Cite

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“…This is intuitive, as these low energy (short D-A distance) exciplexes will be the first to be disrupted as the host is incorporated into the exciplex films. [19][20][21] The net result is this truncates the shorter end of the D-A distance distribution, and therefore limits the extend of the spectral redshift.…”

Section: Equation 1 ∝ -∆mentioning

confidence: 99%

“…Comparison between the PLQY values and the ΔE ST of the CDBP, CBP and mCP based exciplex phosphorescence value measured for CDBP:UGH-3 evaporated films at[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] …”

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confidence: 99%

Identifying the Factors That Lead to PLQY Enhancement in Diluted TADF Exciplexes Based on Carbazole Donors

2019

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Here we compare the effects of solid-state dilution on the photophysical and electrical performance of three TADF exciplexes based on carbazole containing donors with a high-performance acceptor PO-T2T. We observe intrinsically different photophysical behaviour between the exciplexes, which is explained by the presence of a heterogeneous distribution of triplet energies in one of the donor molecules arising from a distribution of planar and highly twisted biphenyl bridges. This study of different donors demonstrates that the recently discovered efficiency enhancement of solid-state diluted exciplexes is independent of the separation associated spectral blueshift, with the latter being universal while the former is only found for donors with low structural rigidity. OLEDs produced from these carbazole based exciplexes show decreased electrical performance likely due to the relatively low conductivity of the donors and host, suggesting that functional conductive hosts may, in some cases, be required to translate optical efficiency enhancements into improved electrical performance.

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“…Therefore, an increasing number of new, optimized, and even multifunctional TADF molecules based on the D-A scaffolds have been developed. [16][17][18] Also, the development of valueadded and multifunctional TADF molecules has tremendous meaning in materials sciences, as they can be used not only in display applications but also in sensing and optical imaging arena. [19] More and more D-A systems comprising of structurally-diverse and large fragments have been reported, but they are still limited to linear and grafted structures.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll‐Off

et al. 2020

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In this work, we present how a small change in molecular structure can affect the electrochemical stability of organic compounds. A new electron donor-acceptor-donoracceptor (D-AD A) macrocyclic π-conjugated compound (tBuMC) comprising of dibenzophenazine as As and N,N'-bis (t-butylphenyl)-p-phenylenediamines as Ds has been synthesized. The photophysical investigation uncovered that tBuMC showed thermally activated delayed fluorescence and that the organic light-emitting diodes (OLEDs) fabricated with tBuMC as the emitter achieved high external quantum efficiency (EQEs) of ca. 10%. However, the OLED with tBuMC showed a slightly lower EQE than that of the OLED with MC (11.6%) and showed greater EQE roll-off. Comparative studies on electrochemical properties of tBuMC, MC, and a linear analogue (Linear) revealed the introduction of t-Bu groups in the D-AD A scaffold causes a significant change in redox behavior. Full electrochemical and spectroelectrochemical studies gave clues to understand how the steric hindering group is affecting the charge distribution in the new molecules which results in a significant difference in the OLED roll-off. The electrochemical investigations together with UV-Vis-NIR and EPR analyses supported by quantum chemical theoretical calculations were performed, which provided us insights on the effect of structural modification on the redox properties of the D-AD A scaffold.

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Emission wavelength dependence on the rISC rate in TADF compounds with large conformational disorder

Abstract: TADF compounds with flexible molecular core show large conformational disorder and emission wavelength instability in solid films.

Cited by 34 publications

References 23 publications

Achieving Submicrosecond Thermally Activated Delayed Fluorescence Lifetime and Highly Efficient Electroluminescence by Fine-Tuning of the Phenoxazine–Pyrimidine Structure

Achieving Submicrosecond Thermally Activated Delayed Fluorescence Lifetime and Highly Efficient Electroluminescence by Fine-Tuning of the Phenoxazine–Pyrimidine Structure

Identifying the Factors That Lead to PLQY Enhancement in Diluted TADF Exciplexes Based on Carbazole Donors

Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll‐Off

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