多环芳烃化合物(PAH)具有大共轭体系,故其分子轨道中包含了能量低的成键π轨道和能量高的反键π~*轨道。当电子吸收合适的能量后,可从能量低的轨道跃迁到能量高的轨道,也称为激发。若被激发电子和未被激发电子的自旋方向相反,得到单重激发态;若自旋方向相同,则得到三重激发态。 Polycyclic aromatic hydrocarbons (PAHs) have a large conjugated system, so their molecular orbitals contain low-energy bond π orbitals and high energy anti-bond π orbitals. When the electrons absorb the right energy, they can jump from low-energy orbitals to high-energy orbitals, also known as excitation. If excited electrons and un-excited electrons spin in the opposite direction, get singlet excited state; if the spin direction is the same, then get the triplet excited state.