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Molecules with Multiple Chiral Centers

Molecules with Multiple Chiral Centers

Molecules that possess multiple chiral centers can afford a large number of stereoisomers. For instance, while some molecules like 2-butanol have one chiral center, defined as a tetrahedral carbon atom with four different substituents attached, several molecules like butane-2,3-diol have multiple chiral centers. A simple formula to predict the number of stereoisomers possible for a molecule with n chiral centers is 2n. However, there can be a lower number where some of the stereoisomers are...

Resonance and Hybrid Structures

Resonance and Hybrid Structures

According to the theory of resonance, if two or more Lewis structures with the same arrangement of atoms can be written for a molecule, ion, or radical, the actual distribution of electrons is an average of that shown by the various Lewis structures.
Resonance Structures and Resonance Hybrids
The Lewis structure of a nitrite anion (NO2−) may actually be drawn in two different ways, distinguished by the locations of the N–O and N=O bonds.

Radical Reactivity: Steric Effects

Radical Reactivity: Steric Effects

The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...

Stereoisomerism

Stereoisomerism

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...

Stereoisomerism of Cyclic Compounds

Stereoisomerism of Cyclic Compounds

In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...

Chirality at Nitrogen, Phosphorus, and Sulfur

Chirality at Nitrogen, Phosphorus, and Sulfur

Chirality is most prevalent in carbon-based tetrahedral compounds, but this important facet of molecular symmetry extends to sp3-hybridized nitrogen, phosphorus and sulfur centers, including trivalent molecules with lone pairs. Here, the lone pair behaves as a functional group in addition to the other three substituents to form an analogous tetrahedral center that can be chiral.
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...

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Related Experiment Video

Updated: Sep 30, 2025

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

Published on: February 6, 2019

Steric Modulation of Spiro Structure for Highly Efficient Multiple Resonance Emitters.

Yang-Kun Qu¹, Dong-Ying Zhou², Fan-Cheng Kong¹

¹Institute of Functional Nano & Soft Materials, Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, 215123, Jiangsu, P. R. China.

Angewandte Chemie (International Ed. in English)

|March 16, 2022

Summary

Introducing spiro-9,9′-bifluorene (SBF) units into multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules prevents aggregation, enhancing device efficiency and narrowing emission bands. This spiro strategy offers a novel approach for high-performance optoelectronic materials.

Keywords:

Fluorescence Multiple Resonance Thermally Activated Delayed Fluorescence OLEDs Spiro Compounds Steric Effects

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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

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Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Published on: July 25, 2022

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Last Updated: Sep 30, 2025

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

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Published on: February 6, 2019

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

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Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Published on: July 25, 2022

Area of Science:

Organic electronics
Materials science
Photophysics

Background:

Fused, planar multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules often suffer from aggregation at high doping, leading to broad emission and reduced efficiency.
Interactions between chromophores in MR-TADF materials can negatively impact device performance.

Purpose of the Study:

To develop a novel design strategy for MR-TADF molecules that mitigates aggregation and enhances device performance.
To investigate the impact of introducing spiro-9,9′-bifluorene (SBF) units at different substitution sites on MR-TADF properties.

Main Methods:

Synthesized MR-TADF molecules incorporating mono-substituted spiro-9,9′-bifluorene (SBF) units.
Fabricated and characterized organic light-emitting diodes (OLEDs) using the synthesized materials.
Analyzed the photophysical properties, including electroluminescence spectra and full width at half maximum (FWHM), at varying doping concentrations.

Main Results:

The introduction of SBF units effectively hindered interchromophore aggregation, even at high doping ratios.
Devices fabricated with SBF-modified MR-TADF emitters achieved high efficiencies (32.2-35.9%) and narrow-band emission (≈27 nm).
The shield-like SF1BN molecule demonstrated minimal FWHM broadening with increasing doping, outperforming its C3-substituted isomer and the parent emitter.

Conclusions:

Mono-substitution with SBF units is an effective strategy for constructing highly efficient MR-TADF emitters.
Steric modulation via spiro structures provides a viable method to control π-framework interactions and improve optoelectronic device performance.
This work presents a promising pathway for designing advanced materials for narrow-band, high-efficiency OLEDs.