Description
Light-responsive molecular switches are powerful tools for controlling chemical and
physical processes with high spatial and temporal precision. Among these systems,
arylazopyrazoles (AAPs) have emerged as an advanced class of photoswitches that
exhibit superior photochemical performance compared to traditional azobenzene
derivatives. Arylazopyrazoles consist of an azo (–N=N–) linkage connecting an aryl ring
to a pyrazole heterocycle, a structural modification that enhances photoisomerization
efficiency, improves thermal stability of the cis isomer, and enables near-quantitative
photoconversion between isomeric states. These compounds characteristically display
strong π-π absorption bands in the UV region, weaker n-π transitions in the visible
region, high molar absorptivity, and tunable electronic properties arising from extended
conjugation and heterocyclic substitution. This work examines the synthesis and
reversible photoswitching behavior of para-bromo (Br-AAP) and 1,8-naphthalimide
functionalized arylazopyrazole (NI-AAP) based molecular switches. The reversible photo-
isomerization properties of the new compounds were characterized by UV–vis absorption
spectroscopy. The results show that the bromo substituted small molecular switches
exhibit efficient reversible trans-to-cis isomerization upon alternating irradiation with UV
( = 365 nm) and green ( = 530 nm). However, the 1,8-naphthalimide substituted
compound displays a partial light-triggered reversible isomerization, suggesting that in
the presence of large substituent the photo-isomerization process was significantly
suppressed. These initial findings establish clear structure–optical property relationships
and confirm the suitability of AAP-based systems as tunable, high-performance molecular
photoswitches for advanced photochemical and materials applications.