Azo hetero arene Photoswitches as Probes for Light induced Phase Transition and Modulating Photoswitching Characteristics and Evaluation of Multiple Azo units Connected Systems

Abstract

Photoswitches are reversibly interconvertible systems between two isomeric states in newlineresponse to light and thus exhibit bistability. Azobenzenes are one of the classic photoswitches newlinetoggling between trans and cis isomers. These are widely studied because of their robustness, newlineease of synthesis, photostability over multiple light irradiation steps, and tunable thermal newlinestability of the photoswitched state. Replacing one or both aryl rings with a five-membered newlineheterocycle ring led to azoheteroarenes, which recently gained widespread attention because newlineof their improved performance and application potential. Currently, tuning the absorption of newlinethe azo chromophore to induce forward E-Z isomerization with longer wavelengths of light and newlinecontrolling their thermal reverse isomerization (cis to trans) are important challenges. Along newlinethe line, imparting distinct physical properties to the isomers through suitable functionalization newlineand controlling them by light are useful in diverse applications. newlineIn the first part, we designed and synthesized azopyrazole photoswitches decorated newlinewith variable N-alkyl and alkoxy chains (for hydrophobic interactions) and phenyl substituents newlineon the pyrazoles to enable and#61552;and#8722;and#61552; stacking. These derivatives showed efficient bidirectional newlinephotoswitching and reversible light-induced phase transition (LIPT). Extensive spectroscopic, newlinemicroscopic, and diffraction studies confirmed the manifestation of molecular-level newlinephotoisomerization into macroscopic changes leading to the LIPT phenomena. Using newlinedifferential scanning calorimetric (DSC) studies, the energetics associated with those newlineaccompanying processes were estimated. The long half-lives of Z isomers, high energy newlinecontents for isomerization and phase transitions, and the stability of phases over an extended newlinetemperature range (-60 to 80 o C) make them excellent candidates for energy storage and release newlineapplications. Also, the difference in the solubility of the distinct phases in one of the derivatives newlineallowed us to utilize it as a photoresist in photolithogr