Polyatomic molecular entities luminesce with appreciable yield only from the lowest excited state of a given multiplicity. There are exceptions to this rule.
Note:
The concept has been extended to the reaction of excited species, i.e., polyatomic
molecular entities react with appreciable yield only from the lowest excited state of a given multiplicity.
Source:
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 360