偶氮型光致变色液晶树状大分子的量子产率、异构转化率和活化能研究

研究了化合物端基含36个己氧基偶氮苯介晶基元的二代(G2)光致变色液晶树状大分子在氯仿及四氢呋喃溶液中的量子产率、吸收光强Ia、活化能E、异构转化率A/A0、热回复异构化速率常数kH及其反/顺异构体组分比A′/A′0,并与一代光致变色液晶碳硅烷树状大分子(G1)及介晶基元化合物(M3)的光化学行为进行了比较.在氯仿及四氢呋喃溶液中的量子产率的顺序均为M3>G1>G2,吸收光强Ia在氯仿及四氢呋喃溶液中的顺序分别为G2>G1>M3(氯仿)和M3>G1>G2(四氢呋喃),在氯仿及四氢呋喃溶液中活化能的顺序均为M3>G2>G1,在氯仿及四氢呋喃溶液中热回复异构化速率常数kH的顺序均为G1>G2>M3,在热回复异构化反应中的反/顺异构体组分比A′/A0′在氯仿及四氢呋喃溶液中的顺序均为G2>G1>M3.

STUDIES ON QUANTUM YIELD, ACTIVATION ENERGY AND PHOTOISOMERIZATION CONVERSION PERCENTAGE OF A PHOTOCHROMIC LIQUID CRYSTALLINE DENDRIMER G2

The photochemical behavior of a photochromic liquid crystalline(LC) dendrimer of the second generation(G2) in chloroform and tetrahydrofuran was described.Thirty-six 4-n-hexyloxyazobenzene mesogenic fragments were attached in its periphery.The photochemical behavior of carbosilane dendrimer of the second generation(G2) was compared with that of the carbosilane dendrimer of the first generation(G1) and the mesogenic unit compound(M3).The quantum yield Φ and intensity of light absorption I_a of G2,G1 and M3 were determined.In chloroform and tetrahydrofuran(THF) Φ was in an order of M3>G1>G2,while I_a in chloroform and tetrahydrofuran(THF) had orders of G2>G1>M3 and M3>G1>G2,respectively.The reaction rate constant of the thermal back-isomerization k_H at different temperature and the activation energy E of G2,G1and M3 were discussed.At the same temperature,k_H in chloroform and tetrahydrofuran(THF) was in an order of G1>G2>M3.The photoisomerization conversion percentage and(trans/cis) isomer absorbance ratio at the thermal back-isomerization of G2,G1 and M3 were described.The photoisomerization conversion percent were in chloroform and tetrahydrofuran(THF) showed orders of G1>M3>G2 and G2>G1>M3,respectively.The(trans/cis) isomer absorbance ratio at the thermal backisomerization A′/A′_0 in chloroform and tetrahydrofuran(THF) was in order of G2>G1>M3.