Polysubstituted 5‐Phenylazopyrimidines: Extremely Fast Non‐ionic Photochromic Oscillators

다국어 초록 (Multilingual Abstract)

Photochromic systems with an ultrahigh rate of thermal relaxation are highly desirable for the development of new efficient photochromic oscillators. Based on DFT calculations, we designed a series of 5‐phenylazopyrimidines with strong push–pull character in silico and observed very low energy barriers for the thermal (Z)‐to‐(E) isomerization. The structure of the (Z)‐isomer of the slowest isomerizing derivative in the series was confirmed by NMR analysis with in situ irradiation at low temperature. The substituents can tune the lifetime of thermal back isomerization from hundreds of microseconds to several nanoseconds (8 orders of magnitude). The photoswitching parameters were extracted from transient absorption techniques and a dominant rotation mechanism of the (Z)‐to‐(E) thermal fading was proposed based on DFT calculations.
An increase in push–pull character of substituted 5‐phenylazopyrimidines accelerates their thermal (Z)‐to‐(E) isomerization to a sub‐microsecond region. The corresponding half‐life can be tuned by proper substitution over 8 orders of magnitude.