激发三重态（Excited three states）
At most temperatures, most molecules are at the lowest vibrational level of the ground state. Molecules absorbed in the ground state absorb energy (electric energy, thermal energy, chemical energy, or light energy, etc.) and are excited to be excited. The excited state is very unstable,
It will relea energy quickly and re jump back to the ground state. When the molecules return to the ground state, the energy is emitted in the form of emission of electromagnetic radiation (light), known as luminescence". If the molecules of matter absorb light energy, they are stimulated
The electromagnetic radiation emitted by the 发票作废
transition back to the ground state, known as fluorescence and phosphorescence. The mechanism of fluorescence and phosphorescence is discusd in terms of molecular structure theory.
Each molecule has a ries of strictly parated energy levels, called electron energy poles, and each electron energy level contains a ries of vibrational energy levels and rotational energy levels. The state of motion of electrons in molecules
In addition to the energy levels, the electrons contain multiple states of electrons. In M=2S+1, S is the s
um of the quantum numbers of each electron spin quantum, with a value of 0 or 1. According to the principle of Pauli incompatibility, the same orbital in the molecule
The two electrons occupied must have opposite spin directions, namely spin pairing. If all electrons in the molecule are spin
paired, then S=0, M=1, the molecule is in a singlet state (or a single line), expresd in symbolic S.
The ground states of most organic compounds are in the singlet state. When the ground state molecules absorb energy, if the electron does not change in the direction of spin during the transition, it is still M=1, and the molecules are excited at a single weight
If the electron is accompanied by a change in the spin direction during the transition, then the molecule has two spin unpaired electrons, S=1, M=3, and the molecule is in the excited three state, expresd in symbolic T.
Fig. 14.1 is a schematic diagram of electronic states.
Fig. 酷狗歌曲
14.1 sketch of excitation of three heavy states in a singlet state
The unpaired electrons in discrete orbits are more stable than spin pairs (especially the rules), so in the same excited state, the energy levels of the three states are always slightly lower than tho of the singlet state.
Fig. 14.2 is a diagram of energy levels and transitions, in which S0, S1 and S2 reprent the ground states of the molecules, the first and cond electron excited singlet states, respectively, and T1 and T2 reprent the three and cond electron excited states of the molecule respectively
. V=0, 1, 2, 3,... Reprents the vibrational level of the
ground state and excited state.
Fig. 14.2 energy level diagram of fluorescence and phosphorescence system
The molecules in the excited state are very unstable, which may be activated by means of radiative transitions and nonradiative transitions (de excitation), releasing excess energy and returning to the ground state.
Radiation transitions are mainly related to fluorescence, delayed fluorescence or phosphorescence emission; nonradiative transition is the relea of excess energy in the form of heat, including vibrati
onal relaxation, internal transfer, intersystem crossing and external transfer
Cheng. Fig. 14.2 reprents the energy transfer process of molecular excitation and deactivation:
(1) vibrational relaxation (Vibration, relaxation, abbreviated as VR) - the transition from the lowest vibrational energy level (V=0) of the ground state to the excited singlet state may be possible when the molecules absorb the radiation of light (a立秋节气
s shown in lambda 1, lambda 2 in Fig. 14.2)
Higher vibrational levels of Sn (as shown in S1 and S2). Then，
In the gas pha where the liquid pha or the pressure is high enough, the collision probability between molecules is large, and the molecules 可爱的动物图片
may pass excess vibrational energy to the surrounding region in the form of heat
Environment, and its transition from the high vibrational energy level of the excited state to the lowest vibrational level of the electron energy level, this process is called vibrational relaxation. The vibrational relaxation time is 10 - 12s orders of magnitude.
(2) internal transfer (Internal, conversion, abbreviated as IC) - when the low vibrational energy levels in the high electron levels overlap with the high vibrational energy levels in the lower electron levels,
electrons frequently occur from the high electron energy levels
The transition from nonradiative to low electron levels. As shown in Fig. 14. and 2, the十月用英语怎么说
low vibrational kinetic energy levels in S2 and T2 overlap with the high vibrational kinetic energy levels in S1 and T1, and electrons can transition from S2 to S1 through the superposition of vibrational levels, or from
T2 transition to T1. This process is called internal transfer. Time transfer for 1011s ~ 1013s magnitude. The rate of vibrational relaxation and internal transfer is much faster than the direct emission of photons by a highly ex己怎么组词
cited state,
Therefore, no matter which excited singlet state excited by the radiation energy, the molecules can jump to the lowest vibrational level via vibrational relaxation and internal transfer to the lowest (first) excited singlet state.
(3) fluorescence emission (Fluorescence, emission, FE) - after
the vibrational relaxation and internal transfer of electrons in the excited singlet state, reach the lowest vibrational level (V=0) of the first excited singlet (S1),
The vibrational levels of the ground state (S0) transition in the form of radiation. The process is fluor
escence emission with a fluorescence wavelength of. The energy loss due to vibrational relaxation and internal transfer, and hence the fluorescence emission energy
The energy is smaller than the molecular absorption, and the wavelength of fluorescence emission is longer than the wavelength of molecular absorption. The average lifetime of the lowest vibrational level in the first excited singlet state is about 10-9 - 10 - 4S, so the fluorescence lifetime is also in the range
This order of magnitude.
(4) department (Intersystem Crossing, ISC Kuayue) - between leap refers to the non radiative transition process between different multiplets, it relates to the electronic excited spin state change.
Such as the transition from the first excited singlet state S1 to the first excited three heavy state T1, so that the two spin pairs of electrons are no longer paired. This transition is prohibited (not in conformity with the spectral lection rule),
But if the two energy layers have a large overlap, the minimum
