Related Experiment Video
Updated: Jul 17, 2026
14:11
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Embedded amide in π-conjugation as a tunable double-bond motif for controlling optical properties
Sho Fukuda1, Daiki Morishita1, Said Jalife2
1Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo Tokyo 113-8656 Japan itoh@chembio.t.u-tokyo.ac.jp.
Chemical Science
|July 16, 2026
Summary
Researchers developed amide-embedded pyrenes (AmPys) by incorporating tunable amide C-N bonds into polycyclic aromatic hydrocarbons. Modulating C-N bond length effectively tuned electronic properties, offering a new design strategy for advanced materials.
Area of Science:
- Organic Chemistry
- Materials Science
- Photophysics
Background:
- Polycyclic aromatic hydrocarbons (PAHs) are crucial in organic electronics.
- Modulating electronic properties of PAHs via heteroatom incorporation is effective but challenging due to structural rigidity.
- Amide bonds offer a potential solution as tunable double-bond units.
Purpose of the Study:
- To introduce and investigate the amide C-N bond as a tunable double-bond unit within PAH frameworks.
- To synthesize and characterize amide-embedded pyrenes (AmPys) with modulated C-N bond characteristics.
- To establish a structure-property relationship between C-N bond length and photophysical properties.
Main Methods:
- Synthesis of amide-embedded pyrenes (AmPys) with cis-amide bonds.
- Modulation of amide C-N bond character via O- and N-methylation, hydrogen bonding, and protonation.
- Spectroscopic studies (UV-Vis absorption, emission) to determine S1 and T1 state energies.
- Computational methods (DFT) to analyze triplet spin densities and nucleus-independent chemical shifts.
Main Results:
- Amide C-N bond length was successfully modulated, influencing the degree of double-bond character.
- A unique inverse relationship was observed between C-N bond length and T1 state energy.
- S1 state energies remained relatively constant, leading to a tunable S1-T1 energy gap (ΔEST).
- Short C-N bonds localized π-conjugation, lowering T1 energies; long C-N bonds delocalized conjugation, raising T1 energies.
Conclusions:
- The amide bond serves as a versatile and tunable double-bond unit in π-conjugated systems.
- C-N bond length is a key design parameter for controlling electronic and photophysical properties, particularly the T1 state energy.
- This approach provides a new strategy for designing functional organic materials with tailored optoelectronic characteristics.
Related Concept Videos
01:19Structure of Amines
The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are illustrated in Figure...
01:27¹H NMR: Long-Range Coupling
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
01:20Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
01:29Preparation of Amides
Amides are synthesized by treating carboxylic acids with amines in the presence of dehydrating agents like dicyclohexylcarbodiimide (DCC).
The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
Subsequently, the amine acts as a nucleophile that attacks the acylating agent to form a tetrahedral intermediate. In the...
The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
Subsequently, the amine acts as a nucleophile that attacks the acylating agent to form a tetrahedral intermediate. In the...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...