Harnessing Coherent Light–Matter Interactions for All-Optical Switching and Logic Gate Applications with Macrocyclic Phthalocyanines

The phase modulation exhibited by the coherent interaction of an intense light as it propagates through a nonlinear optical material, imparting a considerable nonlinear phase shift on another weak light field as they cross each other in the same medium, can be potentially exploited for all-optical switching applications. In this study, we implement this coherent light–matter interaction in π-conjugated organic molecules-based phthalocyanine (Pc) derivatives, namely, one free-base and two metalated (Cu and Zn) phthalocyanine macrocyclic complexes, namely FbPc, CuPc, and ZnPc, respectively. Various nonlinear optical (NLO) parameters are estimated by employing the spatial self-phase modulation (SSPM) technique by considering the variation of the number of diffraction rings formed at a far field with different input excitation intensities for these molecules in both solution and thin films. The estimated range of values for nonlinear refractive index (n₂) and third-order nonlinear susceptibility (χ⁽³⁾) are ∼(1.46–11.13) × 10^–5 cm²/W and ∼(2.53–20.3) 10^–3 esu, respectively. Among all samples, CuPc exhibited the highest NLO response. Using cross-phase modulation (XPM), a combination of intense light and weak light of different wavelengths propagating through these materials, we demonstrated all-optical switching and OR-logic optical gate applications. These complex light–matter interactions show an emerging window for logic gates and all-optical switching applications.