A novel family of azobenzene-based photochromic amorphous molecular materials has been created. They were found to readily form amorphous glasses with well-defined glass-transition temperatures and to exhibit photochromism as amorphous films as well as in solution. It was found that their quantum yields of trans-cis photoisomerization were smaller as amorphous films than in solution and that the backward cis-trans thermal isomerization reactions as amorphous films were either accelerated or retarded relative to those in solution, depending upon their molecular structures. In addition, the rate acceleration for the cis-trans thermal isomerization as amorphous films relative to solution was found to be more prominent as the irradiation time for generating the cis-isomer became shorter.

No abstract

No abstract

No abstract

Low molecular-weight organic compounds generally tend to crystallize readily. We have been performing studies of the creation of low molecular-weight organic compounds that readily form stable amorphous glasses above room temperature, which we refer to as amorphous molecular materials, and investigating their structures, reactions, properties, and applications. [1][2][3][4][5] As a part of these studies, we have studying the creation of low molecular-weight organic photochromic compounds that readily form stable amorphous glasses above room temperature, which we refer to as "photochromic amorphous molecular materials". These compounds may constitute a novel family of photochromic materials that form uniform amorphous thin films by themselves. These materials have an advantage that there is no dilution of photochromic chromophores relative to photochromic polymers and composite polymer systems, where low molecular-weight photochromic compounds may crystallize at high concentration. Based on this new concept, we have designed and synthesized 4-[bis(4-methylphenyl)amino]azobenzene (BMAB) and 4-di(biphenyl-4-yl)aminoazobenzene (DBAB). [6,7] These compounds readily form amorphous glasses with glasstransition temperatures (Tgs) of 27 and 68 °C, respectively, and exhibit photochromism in their amorphous films. It has been found that the fraction of cis-isomer at the photostationary state is smaller in their amorphous films than in the solution. The result indicates that the local free volume is not large enough to allow all the molecules to isomerize from the trans-form to the cis-form in the amorphous film.It is thought that the fraction of cis-isomer at the photostationary state depends on both the size and distribution of local free volume and the volume needed for isomerization from the transisomer to the cis-isomer. In the present study, we have synthesized a new azobenzene derivative, 4-[bis(4-methylpheny)amino]-4'-methoxyazobenzene (MeO-BMAB), and investigated its photochromic behavior in comparison with those of BMAB and DBAB in order to gain information about the relationship between the molecular structure and the fraction of cis-isomer at the photostationary state.The new compound, MeO-BMAB, was found to form readily an amorphous glass when the melt