端基含36个己氧基偶氮苯基元的二代碳硅烷光致变色液晶树状高分子的光化学研究

STUDIES ON PHOTOCHEMISTRY OF A CARBOSILANE PHOTOCHROMIC LIQUID CRYSTALLINE DENDRIMER OF SECOND GENERATION CONTAINING THIRTY_SIX 4_HEXYLOXYAZOBENZENE MESOGENIC GROUPS IN ITS PERIPHERY

研究了含36个己氧基偶氮苯介晶基元的二代(G2)光致变色液晶树枝状高分子在氯仿和四氢呋喃溶液中的最大吸收波长,摩尔消光系数,反顺光异构化反应速率常数,光化学回复异构化正逆反应速率常数及其平衡常数,G2和G1的光致变色反应速率常数kp为10-1s-1,而含偶氮基元光致变色液晶聚硅氧烷的kp为10-8s-1,因此液晶树状高分子的光响应速率比后者快107倍.

The photochemical behavior of a photochromic carbosilane liquid crystalline （LC） dendrimer of second generation （G2） in chloroform and tetrahydrofuran were described. Thirty-six 4-hexyloxyazobenzene mesogenic fragments were attached in its periphery. The maximum absorption wave length and molar extinction coefficient of G2 were determined. The reaction rate constants of trans/cis photochemical isomerization and positive/counter photochemical back-isomerization and the equilibrium constant of photochemical back-isomerization reaction for G2, G1 and M3 were discussed. Their absorbance A350 in CHCl3 and maximum absorption wave length λmax in CHC13 and THF around 360 nm are in G2 〉 G1 〉 M3 and G2 〈 G1 〈 M3 order, respectively. λmax of G2 in solutions shows an order of DMF 〉 C6H6 〉 CHC13 〉 THF 〉 EtOH. Their molar extrinction coefficient ε360 in CHCl3 and THF and their reaction ratio constant of photochemical isomerization kp in CHCl3 are in G2 〉 G1 〉 M3 and G2 〈 G1 〈 M3 orders, respectively. The rate constant of photochromic reaction of G2 is 10^-1s^-1, but that of the photochromic LC polysiloxanes containing the azobenzene moieties is 10^-8s^-1, thus the photoresponsive rate of the LC photochromic dendrimer G2 is 10^7 times larger than that of the latter.