Photochromic Properties of Unsymmetric Mono- and Bis(phenylazo)naphthalenes

Article abstract of DOI:10.1246/bcsj.63.1658

To utilize the reversible photochromic system of phenylazonaphthalenes in a design of functional molecule, the photochromic behaviors of various substituted phenylazonaphthalenes have been investigated.Introduction of substituents onto ortho positions with respect to the azo group retarded the rate of thermal cis-to-trans isomerization.The retardation effects were greatly dependent on both the number and position of the ortho substituents.To investigate the retardation effects of ortho substituents, the activation parameters were determined; the results suggest that the steric hindrance among the ortho substituents and the two nitrogen lone pairs of the azo group becomes far more severe in an inversional transition-state than in the ground cis-state, which leads to the remarkable slow cis-to-trans isomerization.On the basis of the kinetic data of various phenylazonaphthalenes, the complicated isomerization behaviors of unsymmetric bis(phenylazo)naphthalenes have been elucidated.