Singlet oxygen refers to one of two singlet electronic excited states. Singlet and triplet carbenes exhibit divergent reactivity. Statistically three triplet excitons will be formed for each singlet exciton. The two classes of carbenes are singlet and triplet carbenes. The wearing of a T-shirt underneath the singlet is optional. Examples include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. Thus, triplet states generally have longer lifetimes than singlet states. It can act as a scavenger for hydroxyl radicals, singlet oxygen, and various electrophiles. Excited state singlet molecular oxygen is responsible for red chemiluminescence in solution. A concerted mechanism is available for singlet carbenes. Organometallic complexes are often degraded by singlet oxygen. Nic wears a black singlet and medical mask. The black singlet and yellow towel Billy wore in these sketches were to become iconic. In consequence it is a singlet state and is known as singlet oxygen. They help to produce singlet oxygen to damage tumours.