Related Experiment Video
Updated: Aug 11, 2026
13:56
Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations
Published on: October 12, 2019
Engineering Intersystem Crossing in π-Conjugated Molecules through Heavy-Atom Effects: Computational Design Insights
Sonia Das1, Pandiselvi Durairaj1, Durga Mukkonathil1
1Department of Chemistry, National Institute of Technology, Tiruchirappalli620015, India.
The Journal of Physical Chemistry. A
|August 10, 2026
Summary
We enhanced intersystem crossing (ISC) in organic molecules by adding bromine to azabenzanthracene (1-AzBA). This creates efficient ISC for optoelectronic devices, like metal-free organic light-emitting diodes.
Area of Science:
- Organic Chemistry
- Photophysics
- Materials Science
Background:
- Efficient intersystem crossing (ISC) is vital for organic optoelectronics, enabling applications like phosphorescence and delayed fluorescence.
- Azabenzanthracene (1-AzBA) derivatives are explored for their photophysical properties.
Purpose of the Study:
- To investigate excited state properties of 1-AzBA using theoretical methods.
- To design and evaluate a novel 12-Br-1-AzBA structure for enhanced ISC.
- To explore strategies for improving spin-orbit coupling (SOC) in organic systems.
Main Methods:
- Time-dependent density functional theory (TD-DFT) was employed.
- Computational analysis of excited state properties and SOC was performed.
- Bromine substitution effects on 1-AzBA were theoretically modeled.
Main Results:
- A strong SOC of 108.39 cm-1 was achieved between 1ππ* and 3nπ* states in 12-Br-1-AzBA.
- Ultrafast ISC (10^12 s^-1) was predicted, leading to fluorescence quenching.
- The 12-position bromine substitution was identified as uniquely effective for promoting ISC.
Conclusions:
- Bromine incorporation at the 12-position of 1-AzBA significantly enhances ISC via heavy-atom effect and orbital angular momentum changes.
- 12-Br-1-AzBA presents a promising metal-free framework for designing efficient organic materials for optoelectronic applications.
- The study demonstrates a viable strategy for tuning photophysical properties through strategic heavy atom substitution.
More Related Videos
Related Concept Videos
01:24π Molecular Orbitals of 1,3-Butadiene
Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
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...
01:27¹H 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.
01:27π Electron Effects on Chemical Shift: Overview
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...