Scientists develop efficient narrowband circularly polarized light emitters for high-definition OLEDs

Scientists develop efficient narrowband circularly polarized light emitters for high-definition OLEDs

Outcomes:

• Scientists have developed a design strategy to address the issue of broad emission with a large Stokes shift in helicenes, which are one of the most promising classes of circularly polarized luminescence (CPL) active molecules.
• 1,4-B,N-embedded configurationally stable single- and double helicenes were synthesized using this strategy, which exhibited unprecedentedly narrow fluorescence and CPL bands along with high fluorescence quantum yields.
• The helicenes showed a full width at half maximum between 17-28 nm and 0.07-0.13 eV, making them suitable for ultrahigh-definition CP-OLEDs.
• Quantum chemical calculations revealed that the narrow emission was due to the relative localization of the natural transition orbitals on the rigid core of the molecule.

Scientists have developed an efficient narrowband circularly polarized light emitter for high-definition OLEDs. Circularly polarized luminescence (CPL) active molecules such as helicenes are promising, but they typically exhibit broad emission with a large Stokes shift, making them unsuitable for high-definition CP-OLEDs. The researchers used a design strategy that capitalized on intramolecular donor-acceptor interactions between nitrogen and boron atoms to synthesize 1,4-B,N-embedded configurationally stable single- and double helicenes. These helicenes exhibited unprecedentedly narrow fluorescence and CPL bands with high fluorescence quantum yields, making them suitable for ultrahigh-definition CP-OLEDs. Quantum chemical calculations revealed that the narrow emission was due to the relative localization of the natural transition orbitals on the rigid core of the molecule.

Circularly polarized luminescence (CPL) active materials are essential for ultrahigh-definition CP-OLEDs. Helicenes are one of the most promising classes of CPL active molecules, but they typically exhibit broad emission with a large Stokes shift, making them unsuitable for high-definition CP-OLEDs. Scientists at the Zhang research group have developed a design strategy to address this issue. They capitalized on intramolecular donor-acceptor interactions between nitrogen and boron atoms to synthesize 1,4-B,N-embedded configurationally stable single- and double helicenes. Both helicenes exhibited unprecedentedly narrow fluorescence and CPL bands with full width at half maximum between 17-28 nm and 0.07-0.13 eV and high fluorescence quantum yields ranging from 72-85%. Quantum chemical calculations revealed that the narrow emission was due to the relative localization of the natural transition orbitals on the rigid core of the molecule. These efficient narrowband circularly polarized light emitters are suitable for ultrahigh-definition CP-OLEDs.

What this paper is about

• Carbohelicenes, heterohelicenes, and helicenoids have emerged as the preferred molecules to realize circularly polarized luminescence as they offer an excellent chiroptical response.
• However, the dynamic three-dimensional structure of helicenes, via structural reorganization between the S0 and S1 states, leads to broad fluorescence and CPL emissions as well as large Stokes shifts. These shortcomings prevent their broad applicability, especially in ultrahigh-definition CP-OLED devices where narrowband emission is essential.
• While OLEDs require a circular polarizer to achieve high image contrast, which leads to significant energy loss, CP-OLEDs benefit from the direct emission of circularly polarized light.

What you can learn

• The major difference is that carbazole was replaced with azahelicene.
• A diastereomeric mixture of compound 5 was obtained in 65% yield by nucleophilic aromatic substitution of 2-bromo-1,3-difluorobenzene with rac-azahelicene.

Core Q&A related to this research

1. What is the issue with helicenes in terms of circularly polarized luminescence (CPL) emissions?

• Helicenes typically exhibit broad emission with a large Stokes shift, which prevents their broad applicability, especially in ultrahigh-definition CP-OLED devices where narrowband emission is essential.

2. What design strategy was used to address the issue with helicenes’ emissions?

• The design strategy used was to capitalize on intramolecular donor-acceptor interactions between nitrogen and boron atoms to create 1,4-B,N-embedded configurationally stable single- and double helicenes.

3. What were the outcomes of the synthesis of the 1,4-B,N-embedded helicenes?

• The 1,4-B,N-embedded helicenes showed unprecedentedly narrow fluorescence and CPL bands (full width at half maximum between 17–28 nm, 0.07–0.13 eV) along with high fluorescence quantum yields (72–85%).

4. What contribution did quantum chemical calculations make to understanding the emission of the 1,4-B,N-embedded helicenes?

• The quantum chemical calculations revealed that the relative localization of the natural transition orbitals, mainly on the rigid core of the molecule, and small values of root-mean-square displacements between S0 and S1 state geometries, contribute to the narrower emission.

5. How do CP-OLEDs differ from regular OLEDs?

• While regular OLEDs require a circular polarizer to achieve high image contrast, which leads to significant energy loss, CP-OLEDs benefit from the direct emission of circularly polarized light.

Basics Q&A related to this research

What are Carbohelicenes, Heterohelicenes, and Helicenoids?

Carbohelicenes, heterohelicenes, and helicenoids are classes of organic molecules that have a helical structure and offer an excellent chiroptical response.

What is Circularly polarized luminescence (CPL)?

Circularly polarized luminescence (CPL) is a property of some molecules that emit light in a way that the plane of the emitted light waves is circularly polarized, rather than being randomly polarized.

What are Ultrahigh-definition CP-OLEDs?

Ultrahigh-definition CP-OLEDs are devices that use circularly polarized light to display high-contrast images. Unlike OLEDs, they do not require a circular polarizer, which results in significant energy loss.

What is Narrowband emission?

Narrowband emission is a property of some molecules that emit light in a very narrow range of wavelengths, which is essential for applicable circularly polarized luminescence (CPL) active materials in ultrahigh-definition CP-OLEDs.

What are Intramolecular donor-acceptor interactions between nitrogen and boron atoms?

Intramolecular donor-acceptor interactions between nitrogen and boron atoms are a type of chemical interaction that can occur within a molecule where one atom (the donor) donates an electron to another atom (the acceptor). These interactions are used in a design strategy to create narrowband emission molecules that emit circularly polarized light.

What are Configurationally stable single- and double helicenes?

Configurationally stable single- and double helicenes are types of organic molecules with a helical structure that are designed to emit circularly polarized light with narrowband emission properties.

What is Fluorescence?

Fluorescence is a property of some molecules where they absorb light of a particular wavelength and emit light at a longer wavelength.

What is Stokes shift?

Stokes shift is a term used to describe the difference between the wavelength of maximum absorption and the wavelength of maximum fluorescence of a molecule.

What are Quantum chemical calculations?

Quantum chemical calculations are a type of computational chemistry method that uses quantum mechanics to predict the electronic structure and properties of molecules.

What is Chiroptical response?

Chiroptical response is a property of some molecules where they exhibit different optical properties for left and right circularly polarized light.

What are OLEDs?

OLEDs (Organic Light Emitting Diodes) are devices that emit light when a current is passed through a thin film of organic material.

What is a Circular polarizer?

A circular polarizer is an optical device that is used to filter out all but one plane of polarization of a light beam.

What is Azahelicene?

Azahelicene is a type of organic molecule that has a helical structure and is used to create circularly polarized luminescence (CPL) active materials.

What is Nucleophilic aromatic substitution?

Nucleophilic aromatic substitution is a type of organic reaction where a nucleophile replaces a leaving group in an aromatic compound. This reaction is used to synthesize diastereomeric mixtures of molecules such as azahelicene.