The bistable molecular system (1) exhibits temperature-induced phase transition associated with the change of dielectric property and refractive index. The temperature-dependent resonance changes also observed in an integrated optical cavity with 1 embedded in the cladding indicate a high negative TOC of 1 (-0.4 RIU/K) at T ≤ 320 K and TOC ≈ 0 at T ≈ 330 K. This experiment demonstrates the strong potential of 1 for designing efficient and high-performance thermo-optic phase-shift hybrid materials in integrated photonic platforms, especially those with low intrinsic TOC, such as silicon nitride. The tunability of the TOC from large negative values to almost zero at T ≈ 330 K is attractive for reconfigurable photonics , and the zero thermo-optic shift observed at T ≈ 330 K is attributed to the phase transition in the material and can be useful for thermal invariance in integrated photonic systems and photonic switching applications.