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

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.

Molecular photoswitches in aqueous environments

“…157,158 As in classical azobenzenes, the E form is planar and the Z is twisted, adopting either a helical conformation in the case of 6-membered rings, and a T-shaped one if a 5-membered heteroaryl ring is directly attached to the diazo bond. 157,158,165 Moreover, the photophysical properties are influenced by the presence of the hetero atoms, rendering azoswitches based on pyridine, [166][167][168][169][170] indole, [171][172][173][174] indazole, 175 purine, 176,177 pyrimidine, 178,179 pyrrole, 165 imidazole, 165,[180][181][182] pyrazole, 46,165,[183][184][185][186][187][188] oxazole, 189 thiazole, 180 thiophene, [190][191][192] etc., generally responsive to light of longer wavelength. In contrast, in classical azobenzenes the UV-Vis absorption spectrum can be tuned by introducing, for instance, (push-pull) substituents in the para position 156,193,194 or tetraortho substituents [195][196]...…”

Fast Photoswitchable Molecular Prosthetics Control Neuronal Activity in the Cochlea

“…Finally, AMPA receptor desensitization might contribute to the transient response properties. Future work could consider to further speedup thermal relaxation potentially by replacing the current azobenzene unit in TCP fast with faster photoswitches such as (hydroxy-substituted) phenylazopyrimidine (millisecond to nanosecond range 30 − 32 ). However, such accelerated back-switching might in turn result in a lower cis conversion percentage in the photostationary state and, therefore, would require higher light intensity.…”

Advanced NMR Spectroscopy Methods for Study of Structure and Properties of Small Molecules

“…NMR spektra se měří pro daný typ jader, např. 1 H nebo 13 C, která jsou v organické chemii nejběžnější. V molekulách jsou atomová jádra stíněná elektrony, které determinují jejich okolí.…”

“…Pro systémy obsahující strukturně podobné fragmenty se obvykle měří dvoudimenzionální (2D) spektra 2 , ve kterých jednotlivé krospíky představují interakci těch jader, které spolu mají nepřímou spin-spinovou interakci přes chemické vazby, jejíž velikost vyjadřuje interakční konstanta J (J-coupling). Jako příklad lze uvést homonukleární 1 H-1 H korelace (COSY spektrum) nebo heteronukleární 1 H- 13 C korelace (HSQC, HMBC spektra). J-coupling je navíc úzce spjat s dihedrálním úhlem mezi interagujícími jádry, jak popisují Karplusovy křivky, čehož lze využít při studiu stereochemie (konformace/konfigurace) 3 .…”