Abstract
The paper investigates the spectral characteristics of colored polyimide films containing the active bright-green dye 4C. Using spectrophotometry and Fourier-transform infrared (FTIR) spectroscopy methods, the influence of dye concentration on the transmittance and reflectance coefficients of the films was analyzed. Experimental studies demonstrated that increasing the dye content reduces transmittance in the visible spectral region by 22–25% without shifting the spectral maxima, indicating uniform dye distribution within the matrix and the absence of phase segregation. The study confirmed that the introduction of dye 4C leads to the formation of a narrow absorption band at 682 nm, which is a characteristic feature of a stable dyed polymer structure. Additionally, the results showed that the inclusion of the dye accelerates the polyimide formation process. FTIR spectroscopy analysis revealed the presence of additional absorption bands in the 1500–1000 cm⁻¹ range, suggesting possible chemical interactions between the dye and the polyimide matrix. The obtained results confirm the feasibility of using colored polyimide films as active elements in optical filters, sensors, and laser systems. Controlling the dye concentration allows for fine-tuning the optical properties of the films, opening up new prospects for their application in photonics, sensor technologies, and the development of functional materials with predefined spectral characteristics.