The Many Facets of Molecular Orientation in Organic Optoelectronics

Hofmann, Alexander; Schmid, Markus; Brütting, Wolfgang

doi:10.1002/adom.202101004

Cited by 51 publications

(77 citation statements)

References 141 publications

(279 reference statements)

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“…Functional materials and techniques for precise positioning [ 1 , 2 , 3 , 4 , 5 ] and orientational control [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] of single molecules are highly desirable for engineering a new generation of systems and devices that exploit the intrinsic properties of molecules with nanoarchitectural control [ 11 , 12 ]. Although nature uses proteins as templates to orchestrate the directional arrangement of molecules [ 13 ], scientists have harnessed DNA as a programmable polymer [ 1 ], with specific self-assembly via Watson-Crick hydrogen base-pairing rules, to fabricate templates of nanometric spacing.…”

Section: Introductionmentioning

confidence: 99%

Strategies for Controlling the Spatial Orientation of Single Molecules Tethered on DNA Origami Templates Physisorbed on Glass Substrates: Intercalation and Stretching

Cervantes-Salguero

Biaggne

Youngsman

et al. 2022

IJMS

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Nanoarchitectural control of matter is crucial for next-generation technologies. DNA origami templates are harnessed to accurately position single molecules; however, direct single molecule evidence is lacking regarding how well DNA origami can control the orientation of such molecules in three-dimensional space, as well as the factors affecting control. Here, we present two strategies for controlling the polar (θ) and in-plane azimuthal (ϕ) angular orientations of cyanine Cy5 single molecules tethered on rationally-designed DNA origami templates that are physically adsorbed (physisorbed) on glass substrates. By using dipolar imaging to evaluate Cy5′s orientation and super-resolution microscopy, the absolute spatial orientation of Cy5 is calculated relative to the DNA template. The sequence-dependent partial intercalation of Cy5 is discovered and supported theoretically using density functional theory and molecular dynamics simulations, and it is harnessed as our first strategy to achieve θ control for a full revolution with dispersion as small as ±4.5°. In our second strategy, ϕ control is achieved by mechanically stretching the Cy5 from its two tethers, being the dispersion ±10.3° for full stretching. These results can in principle be applied to any single molecule, expanding in this way the capabilities of DNA as a functional templating material for single-molecule orientation control. The experimental and modeling insights provided herein will help engineer similar self-assembling molecular systems based on polymers, such as RNA and proteins.

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Section: Introductionmentioning

confidence: 99%

Strategies for Controlling the Spatial Orientation of Single Molecules Tethered on DNA Origami Templates Physisorbed on Glass Substrates: Intercalation and Stretching

Cervantes-Salguero

Biaggne

Youngsman

et al. 2022

IJMS

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confidence: 99%

Controlling Charge Accumulation Properties of Organic Light‐Emitting Diodes using Dipolar Doping of Hole Transport Layers

Noguchi

Hofmann

Brütting

2022

Advanced Optical Materials

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Although the charge accumulation properties at organic hetero interfaces have been often discussed in terms of the energy barrier to charge injection, it is known that the interface charge due to spontaneous orientation polarization (SOP) also plays a significant role. [5,[9][10][11][12] SOP originates from the macroscopic polarization induced by partial alignment of the permanent dipole moments (PDMs) of polar organic semiconducting materials in evaporated films, [9,13,14] and dominates the charge accumulation properties below the turnon voltage of OLEDs. [5,15,16] SOP has been frequently observed in many common OLED materials, particularly emitters and electron transport materials, though it is very small in most hole transport materials. [5,[17][18][19] Recently, Bangsund et al. have demonstrated that the excess charge accumulation due to SOP can reduce the EQE of OLEDs via exciton-polaron quenching, and EQE can be enhanced by eliminating SOP in the device. [6] Thus far, substrate heating during deposition and use of materials with negligible SOP have been examined to eliminate the excess charge accumulation. [6,7] However, substrate heating can influence the properties of underlayers in the device stack, since SOP is often formed in an emission layer (EML) and electron transport layer (ETL) that are commonly deposited on a hole transport layer (HTL). On the other hand, employing negligible SOP materials limits the possible choice of materials and would not be the best for the overall performance of OLEDs. For instance, many phosphorescent and thermally activated delayed fluorescence emitters also exhibit SOP, and ETL materials with negligible SOP are limited. [5,17] As an alternative method, Afolayan et al. have reported very recently that SOP is efficiently eliminated in a co-evaporated film of ETL and medium density of polyethylene. [8] They demonstrated a higher EQE and longer lifetime of a blue OLED by eliminating the SOP of the ETL. Meanwhile, the benefits of SOP in OLEDs are still controversial, e.g., SOP can improve charge injection efficiency and also affect charge blocking property. [20][21][22][23][24] Thus, exploring methods to control the charge accumulation property while keeping SOP is an important issue to optimize the device performance as well as to understand the role of SOP. In that sense, it will be intriguing to use a device stack with identical It is demonstrated that dipolar doping of hole transport layers (HTLs) controls the density and polarity of the accumulated charge at the critical interface between the HTL and the emission layer (EML) in organic lightemitting diodes (OLEDs). Dipolar doping enables spontaneous orientation polarization (SOP) even in nonpolar HTL, and consequently compensates for the negative interface charge originating from the SOP of the adjacent layer. This concept is applied to a phosphorescent OLED, where bis-4(N-carbazolyl) phenylphosphine oxide (BCPO) is employed as a polar dopant for the HTL. The net interface charge is completely compensated at ≈29.5% of d...

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“…[ 2b ] Moreover, most developed ET molecules have linear or planar structures and their ET abilities are highly dependent on molecular orientation. [ 6 ] However, molecular orientation control is quite troublesome with very limited techniques. [ 7 ] Due to these contradictions, it still remains challenging to achieve good thermal stability, high E T , and orientation‐independent fast ET at the same time for a conventional well‐conjugated molecule.…”

Section: Introductionmentioning

confidence: 99%

Through‐Space Conjugated Electron Transport Materials for Improving Efficiency and Lifetime of Organic Light‐Emitting Diodes

et al. 2022

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Thermally stable electron transport (ET) materials with high electron mobility and high triplet state energy level are highly desired for the fabrication of efficient and stable organic light‐emitting diodes (OLEDs). Herein, a new design strategy of constructing through‐space conjugated folded configuration is proposed to explore robust ET materials, opposite to the widely used planar configuration. By bonding two quinolines to the 9,10‐positions of phenanthrene, two novel folded molecules with high thermal and morphological stabilities and high triplet state energy levels (>2.7 eV) are created. These folded molecules possess excellent ET ability with electron mobilities of three orders of magnitude higher than those of linear and planar counterparts. Theoretical calculation and crystallography analysis demonstrate the through‐space conjugated folded configuration has not only reduced reorganization energy but also enlarged charge transfer integral at various dimensions, bringing about efficient multi‐dimensional ET, independent of molecular orientation. By adopting the folded molecule as ET layers, OLEDs with no matter delayed fluorescence or phosphorescence emitters can achieve high external quantum efficiencies and long operational lifetimes simultaneously. This work paves a new avenue towards robust ET materials to improve efficiency and stability of OLEDs.

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The Many Facets of Molecular Orientation in Organic Optoelectronics

Cited by 51 publications

References 141 publications

Strategies for Controlling the Spatial Orientation of Single Molecules Tethered on DNA Origami Templates Physisorbed on Glass Substrates: Intercalation and Stretching

Strategies for Controlling the Spatial Orientation of Single Molecules Tethered on DNA Origami Templates Physisorbed on Glass Substrates: Intercalation and Stretching

Controlling Charge Accumulation Properties of Organic Light‐Emitting Diodes using Dipolar Doping of Hole Transport Layers

Through‐Space Conjugated Electron Transport Materials for Improving Efficiency and Lifetime of Organic Light‐Emitting Diodes

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