singlet
Quick Summary
In physics, a singlet state refers to a quantum mechanical state where the total spin of a system is zero. This typically occurs when two particles, such as electrons, have opposite spins that cancel each other out. This cancellation results in a net magnetic moment of zero, making systems in a singlet state diamagnetic.12
The concept of spin is fundamental to classifying subatomic particles. Particles with half-integer spin values (like 1/2) are called fermions, while those with integer spin values (like 0 or 1) are called bosons. The Pauli exclusion principle dictates that no two electrons in an atom can have the same set of quantum numbers, including spin. Therefore, when two electrons occupy the same orbital, they must have opposite spins, forming a singlet state.312
The EPR paradox, proposed by Einstein, Podolsky, and Rosen, highlighted the peculiar nature of singlet states in entangled particles, suggesting that quantum mechanics might be incomplete.4
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photochemical reactionConsequences of photoexcitation…the molecule is in a singlet state, which is the pattern for the ground state of most molecules. When the molecule is excited (e.g., by absorption of a photon), one electron is promoted to a previously unoccupied orbital, and, if its spin does not change, then the two (now unpaired)…
Read More…the molecule is in a singlet state, which is the pattern for the ground state of most molecules. When the molecule is excited (e.g., by absorption of a photon), one electron is promoted to a previously unoccupied orbital, and, if its spin does not change, then the two (now unpaired)…
Read More- photochemical reactionConsequences of photoexcitation
The higher excited singlet states (S2, S3, and so on, often generally denoted Sn) internally convert rapidly to S1, the excited state with the lowest energy. Internal conversion from S1 to S0, the lowest-energy (or ground) state, is much slower, allowing time for the molecule to either emit…
Read MoreThe higher excited singlet states (S2, S3, and so on, often generally denoted Sn) internally convert rapidly to S1, the excited state with the lowest energy. Internal conversion from S1 to S0, the lowest-energy (or ground) state, is much slower, allowing time for the molecule to either emit…
Read More - photochemical reactionConsequences of photoexcitation
…more strongly than those of singlet states (with opposing spins), the energy difference T1 − S0 is less than S1 − S0, and phosphorescence occurs at longer wavelengths than fluorescence. Also, the low probability of a spin change results in the long-lived nature of phosphorescence observed by Cellini in 1568…
Read More…more strongly than those of singlet states (with opposing spins), the energy difference T1 − S0 is less than S1 − S0, and phosphorescence occurs at longer wavelengths than fluorescence. Also, the low probability of a spin change results in the long-lived nature of phosphorescence observed by Cellini in 1568…
Read More - photochemical reactionConsequences of photoexcitation
The excited singlet and triplet states may also absorb radiation and reach higher excited electronic levels. In general, this transient absorption spectrum is different from the absorption of the ground state, which allows monitoring of the time evolution of the excited states. This is accomplished by a…
Read MoreThe excited singlet and triplet states may also absorb radiation and reach higher excited electronic levels. In general, this transient absorption spectrum is different from the absorption of the ground state, which allows monitoring of the time evolution of the excited states. This is accomplished by a…
Read More - photochemical reactionPhotosensitization
…change in spin to its singlet ground state. The molecular oxygen begins in its triplet ground state and also changes spin to a singlet excited state. Because the total spin between the two molecules is unchanged, the transfer of energy can occur rapidly and efficiently. The resulting molecular oxygen singlet…
Read More…change in spin to its singlet ground state. The molecular oxygen begins in its triplet ground state and also changes spin to a singlet excited state. Because the total spin between the two molecules is unchanged, the transfer of energy can occur rapidly and efficiently. The resulting molecular oxygen singlet…
Read More - photochemical reactionPhotoprotection
…carotenoids are unable to sensitize singlet molecular oxygen and actually quench it, dissipating the energy safely as heat and leaving harmless ground-state molecular oxygen. This antioxidant effect also protects animals and plants from singlet molecular oxygen generated during biological processes and is the reason for the large medical interest in…
Read More…carotenoids are unable to sensitize singlet molecular oxygen and actually quench it, dissipating the energy safely as heat and leaving harmless ground-state molecular oxygen. This antioxidant effect also protects animals and plants from singlet molecular oxygen generated during biological processes and is the reason for the large medical interest in…
Read More - photochemical reactionPhotochemical steps in photosynthesis
…susceptible to photodamage from photosensitized singlet molecular oxygen, but they are protected by carotenoids (photoprotection). The carotenoids also act as light harvesters, absorbing radiation in the blue and green-orange where chlorophyll has little absorption, and transfer this electronic energy to chlorophyll for its eventual delivery to the reaction centre.
Read More…susceptible to photodamage from photosensitized singlet molecular oxygen, but they are protected by carotenoids (photoprotection). The carotenoids also act as light harvesters, absorbing radiation in the blue and green-orange where chlorophyll has little absorption, and transfer this electronic energy to chlorophyll for its eventual delivery to the reaction centre.
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