Saturable to reverse saturable absorption switching in dicyanomethylene-4H-pyran derivatives with their photophysical and nonlinear optical investigation

In the present research, the two dicyanomethylene-4H-pyran derivatives M4 and M5 have been synthesized and characterized for nonlinear optical response. The photophysical properties were investigated through UV-Vis absorption and emission studies. The polarity-dependent salvatochromic study has been performed to confirm intramolecular charge transfer (ICT) occurring in both compounds. The third-order optical nonlinearities have been enumerated using Z-scan techniques with a diode laser (520 nm) and both the compounds exhibit selfdefocusing behavior and saturable absorption behavior. The rare phenomenon i.e. nonlinear absorption switching from saturable to reverse saturable has also been highlighted in both compounds, this inherent property makes the material an effective component for optical limiters. The nonlinear optical susceptibility (chi ((3))), absorption coefficient (beta), and refractive index (n(2)) were calculated to vary linearly with solution concentrations, and both materials reveal their potential in optoelectronic devices.