Thioxanthone

Thioxanthone is a sulfur-containing heterocyclic aromatic ketone that belongs to the xanthenes family. It is closely related to xanthone but contains sulfur in its fused ring system. The compound is a yellow crystalline solid with good solubility in common organic solvents and limited water solubility. It absorbs ultraviolet light and exhibits efficient intersystem crossing to a long-lived triplet state, properties that make it useful as a photosensitizer in various photochemical processes.

In polymer chemistry, thioxanthone is widely employed as a Type II photoinitiator or photosensitizer. In the presence of a co-initiator, such as a tertiary amine or phosphine, the excited thioxanthone abstracts a hydrogen from the donor, generating radicals that initiate polymerization of acrylates, methacrylates, and related monomers. Derivatized thioxanthones extend light absorption and improve initiation efficiency; the two most common derivatives are 2-isopropylthioxanthone (ITX) and 2-ethylthioxanthone (ETX).

Apart from initiating photopolymerization, thioxanthone derivatives are used in photoinitiator systems for coatings, inks, and adhesives that cure under UV light or visible LEDs. They are typically paired with co-initiators to achieve rapid cure at low light intensities and can enable polymerization under household or industrial LED sources.

Thioxanthone and its derivatives are commercially available and are used under standard chemical safety and handling practices appropriate for organic photoinitiators.