If the value of 𝑓 𝑎 ̅̅̅ 𝑜𝑟 𝑓 𝑏 ̅̅̅ is less than 2, it means the monomer contains a compound with just one reactive site, which can be regarded as the quencher, the number of the quenchers can be calculated through Eq. ( ) if 𝑓 𝑛𝑏 ̅̅̅̅ was expected as a constant value.