2,4,5,6-Tetra(9H-carbazol-9-yl)isophthalonitrile
[CAS# 1416881-52-1]

Identification

• Classification: Pharmaceutical intermediate >> OLED material intermediate
• Name: 2,4,5,6-Tetra(9H-carbazol-9-yl)isophthalonitrile
• Synonyms: 2,4,5,6-Tetra-9H-carbazol-9-yl-1,3-benzenedicarbonitrile
• Molecular Formula: C₅₆H₃₂N₆
• Molecular Weight: 788.89
• CAS Registry Number: 1416881-52-1
• EC Number: 863-265-9
• SMILES: C1=CC=C2C(=C1)C3=CC=CC=C3N2C4=C(C(=C(C(=C4C#N)N5C6=CC=CC=C6C7=CC=CC=C75)N8C9=CC=CC=C9C1=CC=CC=C18)N1C2=CC=CC=C2C2=CC=CC=C21)C#N

Properties

• Solubility: Insoluble (7.6E^-11 g/L) (25 ºC), Calc.^*
• Density: 1.32±0.1 g/cm³ (20 ºC 760 Torr), Calc.^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (©1994-2015 ACD/Labs)

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H302-H312-H315-H319-H332-H335
• Precautionary Statements: P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332
Eye irritation	Eye Irrit.	2A	H319

Discovory and Applicatios

2,4,5,6-Tetra(9H-carbazol-9-yl)isophthalonitrile, with the molecular formula C₅₆H₃₂N₆, is an organic compound featuring an isophthalonitrile core substituted with four carbazole groups at the 2,4,5,6-positions. It is recognized in organic chemistry as a key material in organic electronics and photonics, particularly for its role in thermally activated delayed fluorescence (TADF) applications. Its discovery and applications are well-established in the literature, stemming from the development of carbazole-based chromophores and electron-deficient aromatic systems.

The discovery of 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile is rooted in the exploration of carbazole derivatives, which began in the early 20th century due to their photophysical properties and presence in natural products. Carbazole, a nitrogen-containing heterocycle, became significant in the mid-20th century for its electron-donating and hole-transporting capabilities in organic materials. The attachment of multiple carbazole units to electron-withdrawing cores, such as isophthalonitrile, gained traction in the 2000s as researchers sought to design molecules with efficient TADF for organic light-emitting diodes (OLEDs). The specific tetra-substitution pattern emerged to maximize donor-acceptor interactions, leveraging the electron-accepting dicyano core and the electron-donating carbazoles to achieve a small energy gap between singlet and triplet excited states, a hallmark of TADF materials. Advances in N-arylation and cross-coupling techniques during the 1990s enabled the precise synthesis of such highly substituted aromatics.

Synthetically, 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile is prepared via a multi-step process centered on N-arylation. A common route involves the reaction of 2,4,5,6-tetrafluoroisophthalonitrile or 2,4,5,6-tetrachloroisophthalonitrile with carbazole under copper- or palladium-catalyzed Ullmann or Buchwald-Hartwig coupling conditions. The halogenated isophthalonitrile precursor is synthesized from isophthalonitrile through electrophilic halogenation, ensuring the 2,4,5,6-tetrahalo substitution. The coupling reaction uses a catalyst, such as copper(I) iodide or palladium acetate, with a ligand like 1,10-phenanthroline and a base like potassium carbonate, to attach the carbazole nitrogen to the aromatic core. High temperatures and inert conditions ensure complete substitution, forming the tetra-carbazole product. The reaction’s efficiency relies on optimized conditions to overcome steric hindrance from multiple carbazole units. These methods are grounded in well-established protocols in heterocyclic synthesis and transition-metal catalysis.

The primary application of 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile is in organic electronics, particularly as a TADF emitter in OLEDs. The molecule’s design, with four electron-donating carbazole groups surrounding an electron-accepting dicyano core, creates a highly efficient donor-acceptor system. This structure minimizes the energy difference between singlet and triplet states, enabling reverse intersystem crossing and allowing triplet excitons to contribute to fluorescence, achieving near-100% internal quantum efficiency. It is widely used in blue and green OLEDs, offering high brightness, color purity, and energy efficiency. Its thermal and morphological stability, due to the bulky carbazole units, makes it suitable for vacuum-deposited or solution-processed devices. The compound is also explored in organic photovoltaics and fluorescent sensors, where its strong emission and charge-transport properties are advantageous.

In academic research, the compound is studied for its photophysical properties, including TADF mechanisms, excited-state dynamics, and charge-transfer characteristics. Its synthesis has contributed to advancements in high-degree N-arylation and the design of TADF materials. The molecule’s solubility in organic solvents and robust solid-state morphology support its use in flexible electronics. Additionally, it is investigated for applications in photochemical catalysis and molecular probes, leveraging its emissive and redox properties.

The significance of 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile lies in its role as a high-performance TADF material, combining the electron-donating carbazole units with an electron-accepting isophthalonitrile core. Its development reflects progress in donor-acceptor system design and cross-coupling chemistry. By enabling efficient, high-performance organic electronics, it has become a critical tool in advancing materials science and photonics research.

References

2013. Solvent Effect on Thermally Activated Delayed Fluorescence by 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene. The Journal of Physical Chemistry A, 117(25).
DOI: 10.1021/jp404120s

2015. Organic Semiconductor Electroluminescent Materials. Organic Optoelectronic Materials, 1.
DOI: 10.1007/978-3-319-16862-3_6

2019. A window to trap-free charge transport in organic semiconducting thin films. Nature Materials, 18(12).
DOI: 10.1038/s41563-019-0473-6