Efficient Electrocatalytic Switching of Azoheteroarenes in the Condensed Phases

Abstract

Azo-based photoswitches have shown promise as molecular solar-thermal (MOST) materials due to their ability to store energy in their metastableZisomeric form. The energy is then released, in the form of heat, upon photoisomerization to the thermodynamically stableEform. However, obtaining a high energy density and recovering the stored energy with high efficiency requires the materials to be employed in the condensed phase and display a high degree ofZtoEswitching, both of which are challenging to engineer. Here, we show that arylazopyrazole motifs undergo efficient redox-inducedZtoEswitching in both the solution and the condensed phase to a higher completeness of switching than achieved photochemically. This redox-initiated pathway lowers the barrier ofZtoEisomerization by 27 kJ/mol, while in the condensed phase, the efficiency of electrochemical switching is improved by over an order of magnitude relative to that in the solution state. The influence of the photoswitch’s phase, electrical conductivity, and viscosity on the electrochemical switching in the condensed phase is reported, culminating in a set of design rules to facilitate further investigations. We anticipate the use of an alternative stimulus to light will facilitate the application of MOST materials in situations where phototriggered heat release is unachievable or inefficient, e.g., indoor or at night. Furthermore, exploiting the electrocatalytic mechanism, whereby a catalytic amount of charge triggersZtoEswitching via a redox process, bypasses the need for fine tuning of the photoswitching chromophore to achieve completeZtoEswitching, thus providing an alternative approach to photoswitch molecular design.