M-Terphenyl
[CAS 26140-60-3]

Identification

• Classification: Organic raw materials >> Aryl compounds >> Biphenyl compounds
• Name: M-Terphenyl
• Synonyms: 1,3-diphenylbenzene
• Molecular Formula: C₁₈H₁₄
• Molecular Weight: 230.30
• CAS Registry Number: 26140-60-3
• EC Number: 247-477-3
• SMILES: C1=CC=C(C=C1)C2=CC(=CC=C2)C3=CC=CC=C3

Safety Data

• Hazard Symbols: GHS07;GHS09 Warning
• Risk Statements: H317-H400-H410
• Safety Statements: P261-P272-P273-P280-P302+P352-P321-P333+P317-P362+P364-P391-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin sensitization	Skin Sens.	1	H317
Acute toxicity	Acute Tox.	4	H302

chemBlink Chemical Story

Three benzene rings can do more than make a hydrophobic aromatic solid. In m-terphenyl, also called 1,3-diphenylbenzene, the two outer phenyl rings are attached at the meta positions of the central ring. That geometry gives the molecule a photophysical identity different from its better-known para isomer and has made m-terphenyl useful as a fluorescent aromatic building block and, in modern detector materials, as a scintillation fluor.

A scintillator converts invisible ionizing radiation into visible or near-visible photons. When energetic particles or radiation deposit energy in an organic material, excited electronic states are created. The challenge is to move that excitation efficiently into fluorescent molecules that can emit light rapidly enough to be detected by photomultipliers or silicon photomultipliers. Aromatic compounds are well suited because their delocalized pi-electron systems support accessible excited states and fast fluorescence.

Recent work on lithium-loaded plastic scintillators illustrates a concrete role for m-terphenyl. One reported material used about 30% m-terphenyl as the primary fluor, together with a secondary wavelength-shifting dye and lithium-6-containing components. Neutron capture by lithium-6 produces charged particles that deposit energy in the scintillator; the organic matrix and fluor system then convert part of that energy into detectable light. Pulse-shape information can help distinguish neutron events from gamma-ray backgrounds.

Why m-terphenyl rather than simply extending conjugation in a straight line? Meta linkage interrupts electronic communication compared with para linkage. The three rings are also non-coplanar because of steric interactions. This limits effective conjugation and changes absorption, emission, packing, and excited-state behavior. Modern photophysical studies use meta-terphenyl linkers precisely because their electronic communication can be weaker or more geometry-dependent than fully para-connected aromatic systems.

The CAS identity deserves a small note. PubChem lists m-terphenyl under CAS 26140-60-3 and also records the historically common CAS 92-06-8 for the same compound identity in different source systems. The molecular structure itself is straightforward: C₁₈H₁₄, 1,3-diphenylbenzene.

m-Terphenyl is therefore memorable because it connects basic aromatic structure to a very visible outcome. Radiation that cannot be seen deposits energy; aromatic excited states move that energy; fluorescence turns it into photons an instrument can count. Three benzene rings arranged in the right geometry become part of a device for seeing the otherwise invisible.

References:
1. PubChem, m-Terphenyl, CID 7076, CAS 26140-60-3 / 92-06-8.
2. Characterization of ⁶Li-loaded pulse-shape-discriminating plastic scintillators. Nuclear Instruments and Methods in Physics Research A. 2025, 171212.
3. Kim M.-J. et al. meta-Terphenyl linked donor-pi-acceptor dyads. RSC Advances. 2021, 11, 34945-34954. DOI: 10.1039/D1RA06602A.
4. Photophysical studies of m-terphenyl derivatives and aromatic scintillators.

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