Second harmonic responses of clickable azobenzenes in solution: Comparative Hyper-Rayleigh scattering and density functional theory studies

The linear and second-order nonlinear optical (NLO) properties of clickable azobenzene derivatives are investigated in chloroform solution by means of UV/Visible and Hyper-Rayleigh scattering (HRS) spectroscopies. Their absorption properties are also monitored along time in order to characterize the rate and kinetics of the E-Z photoswitching reaction. The magnitude and symmetry of the first hyperpolarizability of the compounds are rationalized with the help of DFT calculations, which support well the experimental data. We demonstrate that the second harmonic generation (SHG) intensity of the E form, as well as its variation upon photoisomerization, can be tuned by varying the nature of the peripheral substituents. A fully characterized library of ready-to-click switchable compounds displaying large hyperpolarizability contrasts, and differing in the amplitude and orientation in their dipole moments is provided. This library expands the database of photoswitching compounds for further anchorage into polymer matrices or nano- or micro-sized solid substrates.