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Factors that dyes fade under the sun
Apr 24, 2018

The effect of light on the attack of dye

When a dye molecule absorbs the energy of one photon, it causes the outer valence electrons of the molecule to jump from the ground state to the excited state.

According to the structure, the dye molecules can attack different intensification processes at different wavelengths, such as pi, pi *, N - pi *, CT (charge transfer), S - S (Dan Xiantai), S to T (San Xiantai), ground state, first excited state and ground state - second intensification state. The ground state of the singlet is written in S0, first and second intensifies the singlet and S1 and S2. The corresponding three linear states are indicated by T0, T1 and T2.

In the process of intensification, the dye molecules are stimulated into a variety of oscillating energy levels, and their oscillating energy levels fall quickly, and the energy is converted to heat and lost. The process of the decline level is called oscillating passivation. In the process of oscillating passivation, the S2 excited state with low oscillation energy level will also become a S1 excited state with high oscillation energy level, and will continue to oscillate passivation. In this way, the S2 excited state with higher energy level is transformed into the S1 excited state of the lowest oscillation level. The transformation between S2 and S1 states under the condition of equal energy intersection does not include the change of electron spin multiplicity, it is called internal transformation. The transition between singlet and three line states will also change from S1 to T1. The transformation of electron energy with the change of electron spin multiplicity under the condition of equal energy intersecting is called intersystem crossing. Because of the "forbidden" rule of electronic spin selection, the rate of intersystem crossing is generally low.

Factors affecting the light fastness of the dye

1. light sources and bright wavelengths;

2. environmental factors;

The chemical properties and arrangement structure of 3. fibers;

4. the bond strength of the dye with the fiber;

5. the chemical structure of the dye;

6. the concentration and the set state of the dye;

7. artificial sweat on the color fading of dye;

8. auxiliaries.

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