Singlet oxygen is an emissive ligand.

Unprecedented experimental evidence shows that gaseous singlet oxygen ( 1 O 2 ) acts as an emissive ligand following collisional photosensitization. This evidence was obtained by monitoring 1 O 2 phosphorescence intensity at ≈1275-1280 nm and the excited state lifetime of singlet oxygen generated by known tetraphenylporphyrin photosensitizers, while varying the atmospheric environment.