The photoisomerization was carried out on a 1.0 cm-path-length quartz cell places on a 4-sided cuvette holder (Cuvette Holder with Four Light Ports, CVH100 Thorlabs). Unless otherwise specified, the concentration of the samples was of 40 µM. The kinetics of the photoisomerization process were measured by following the absorption spectrum during irradiation by selected lightemitting diodes (LED), placed perpendicular to the absorbance measurement. To reach the PPS, the E-isomer was irradiated at the pp* band using a M375L4.1540 mW LED (LED Power Output 1540 mW, 2% power used) with a central wavelength of 375 nm and a bandwidth (FWHM) of 9 nm. For the reverse transformation, Z®E isomerization, the compound was excited at the np* band using a M300L4.32 mW LED (LED Power Output: 47 mW, full power used) with a central wavelength of 300 nm with a bandwidth (FWHM) of 20 nm. The thermal return process between Z and E-isomers was analyzed by measuring the changes of the maximum absorbance wavelength at 25 and 40°C, respectively. Kinetic monitoring of the absorbance was performed using an Ocean Optics USB2000 + XR CCD sensor and kinetic constants were determined using "Biokine" software.