Photochemical study of photochromic liquid crystalline dendrimer of the second generation containing nitro groups

The molar extinction coefficient, maximum absorption wavelength, reaction rate constants of trans/cis photochemical isomerization, thermal back-isomerization and photochemical back-isomerization and equilibrium constant of photochemical back-isomerization reaction of a novel photochroniic liquid crystalline dendrimer (G(2)) of the second generation containing nitroazophenyl groups on its periphery in solution were described. Photochromic reaction rate constant of G(2) in CHCl3 and THF was 10(-1) s(-1), but that of photochromic side-chain polysiloxanes containing azophenyl moieties was 10(-8) s(-1), thus the photoresponsive rate of the liquid crystalline dendrimer G(2) is 10(7) times larger than that of the latter. The equilibrium constant k(t)/k(c) of photochemical back-isomerization reaction of G(2) are 1.77 similar to 1.97 approaching to 1, and thus it is applicable to photoswitch materials.