The disclosure relates to a substituted cyclooctatetraene triplet excited-state quencher compound of Formula (I): wherein: Z is a wide band gap moiety; L is a non-conjugating linker group; each R, which may be the same or different, is a non-conjugating substituent; n is an integer from 0 to 7; and m is an integer from 1 to 6. The disclosure further relates to use of such compounds as triplet quenchers, compositions comprising such compounds, films or coatings comprising said compounds or compositions, and use of said compositions or films or coatings as active gain media for light amplification.