thallene

from The Century Dictionary.

• noun A greenish-yellow, highly fluorescent hydrocarbon, possibly isomeric with anthracene, contained in the highest boiling portion of Pennsylvania crude petroleum. It forms small acicular crystals.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A hydrocarbon obtained from coal-tar residues, and remarkable for its intense yellowish green fluorescence.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry A hydrocarbon obtained from coal tar residues, remarkable for its intense yellowish-green fluorescence.