Singlet oxygen

Some air is very busy. It is a special kind of gas. This gas is made of two oxygen parts. It is stronger than the air we breathe.

This busy gas can change many things. It can even help doctors. It can also help make new things in a lab.

When this gas loses its energy, it glows. It makes a red light. This happens as it turns back into normal air. It is a very busy gas indeed!

Most oxygen is in a quiet state. We call this triplet oxygen. It is the normal air we breathe. But sometimes, oxygen becomes very active. This is called singlet oxygen.

Singlet oxygen is a gas made of two oxygen atoms. In this state, the electrons are paired up. This makes the gas much more reactive. It can change other things very quickly.

This gas can be helpful or harmful. In a lab, scientists use it to make new chemicals. Doctors also use it in photodynamic therapy. This is a way to treat people using light.

But singlet oxygen can also cause damage. It can break down many materials. In the air, it helps make nitrogen dioxide. This can hurt our lungs. In plants, it can be made during photosynthesis. Special parts of the plant help stop this damage. When singlet oxygen loses its power, it turns back into normal oxygen. As it changes, it gives off a red glow.

Oxygen is a gas that usually stays in a quiet state. We call this the triplet ground state. But sometimes, oxygen enters an excited state. This is called singlet oxygen.

It is a gas made of two oxygen atoms. In this state, the electrons are spin-paired. This means the electrons are matched up in a specific way. This makes the gas much more reactive than normal oxygen. It can change other materials very quickly.

Singlet oxygen works differently because of its electrons. In the normal triplet state, electrons are unpaired. To make singlet oxygen, an electron must "flip" its spin. This creates a new state called the 1Δg state. This state has much higher energy than the triplet state. This energy is about 94.3 kilojoules per mole. When singlet oxygen loses this extra energy, it decays back to the triplet state. As it decays, it can release a red glow.

Scientists have found many ways to make this gas. One way is to shine light on oxygen. They use a special dye called a sensitizer to help. Common dyes include rose bengal or methylene blue. You can also make it using chemicals in a lab. For example, mixing hydrogen peroxide with sodium hypochlorite works.

Some methods work well in liquids. Other methods are better for dry conditions.

This gas behaves in many different ways in nature. In the air, it can help form nitrogen dioxide. This is a gas that can hurt human lungs. It also appears in pine forests. There, it coexists with ozone near turpentine.

In plants, it can be made during photosynthesis. Plants use special parts called carotenoids to stop it. These parts help protect the plant from damage.

Singlet oxygen is useful in many important fields. Doctors use it in photodynamic therapy to treat people. In chemistry, it helps build new organic molecules. It can react with things like citronellol or furans.

This is called photooxygenation. However, it can also be harmful to living things. It is linked to the oxidation of cholesterol in mammals. Scientists study these reactions to understand how to stay healthy.

Singlet oxygen, also known as dioxygen(singlet) or dioxidene, is a highly reactive gaseous inorganic chemical. It consists of two oxygen atoms in an excited quantum state. In this state, all of the electrons are spin-paired. This is different from the most common form of oxygen, known as the triplet ground state. While the physical properties of singlet oxygen are similar to normal oxygen, its chemical reactivity is much higher. It is capable of reacting strongly with many organic compounds. This reactivity makes it both a tool for chemists and a factor in environmental processes.

The behavior of singlet oxygen is defined by its electronic structure. In the standard triplet ground state, denoted as 3Σ, the oxygen molecule has two unpaired electrons. These electrons have the same spin, following Hund's first rule. To create singlet oxygen, these electrons must change their arrangement. One way this happens is when one electron "flips" its spin to pair with the other. This creates the 1Δg state, which is the most stable form of singlet oxygen. Another possible state is the 1Σ state, where both electrons remain in separate orbitals but have opposite spins. The 1Δg state is 94.3 kilojoules per mole higher in energy than the triplet ground state. The 1Σ state is even higher, at 157.0 kilojoules per mole.

Scientists can produce singlet oxygen through several different mechanisms. A common photochemical method involves shining light on oxygen gas. This process requires a sensitizer, which is an organic dye like rose bengal, methylene blue, or porphyrins. Chemical methods can also be used without light. For example, reacting hydrogen peroxide with sodium hypochlorite in an aqueous solution produces singlet oxygen. Another method involves the decomposition of phosphite ozonides. This specific technique is useful because it works well in non-aqueous conditions.

The lifespan of singlet oxygen depends heavily on its environment. In a gas phase, the 1Δg state is relatively long-lived, lasting between 54 and 86 milliseconds. However, when it interacts with solvents, its lifetime drops significantly to microseconds or even nanoseconds. In 2021, researchers measured the lifetime of airborne singlet oxygen at air/solid interfaces to be 550 microseconds. The higher 1Σ state is also moderately short-lived. In gases, it has a mean lifetime of 11.8 seconds, but in solvents like carbon disulfide, it quickly relaxes into the lower 1Δg state.

In the natural world, singlet oxygen plays many complex roles. It is found in trace amounts in the upper atmosphere and in polluted urban areas. In these environments, it can contribute to the formation of nitrogen dioxide, which can damage lungs. It also appears in pine forests where it coexists with ozone during the photodegradation of turpentine. Within plants, singlet oxygen can be produced from light-harvesting chlorophyll molecules during photosynthesis. To prevent damage, plants use carotenoids. These molecules help by removing excess light energy or by quenching the singlet oxygen molecules directly.

In biology and medicine, singlet oxygen has both dangerous and helpful effects. In mammals, it is a reactive oxygen species linked to the oxidation of LDL cholesterol. This process can have cardiovascular effects. On the other hand, doctors use it constructively in photodynamic therapy. This medical treatment uses light-activated pigments to target specific cells.

Additionally, some pigments can cause photosensitivity in the skin when activated by light, which is a concern for both humans and herbivorous animals.

Chemists use the unique reactivity of singlet oxygen to build new molecules through processes like photooxygenation. It can participate in Diels–Alder [4+2] and [2+2] cycloaddition reactions. It also performs formal concerted ene reactions, such as the Schenck ene reaction. For instance, it can react with furans or oxidize thioethers into sulfoxides. When it reacts with certain molecules like citronellol, it can lead to the formation of allyl hydroperoxides. These can then be reduced to create useful allyl alcohols. Even in water, it can form an unusual molecule called trioxidane, which contains three linked oxygen atoms.