Binder-endowed thermal stability of diimmonium dye-based near-infrared (NIR) absorbing films

The near-infrared (NIR) absorbing film is a film to block unnecessary near-infrared light. The NIR absorbing film is one of the main components to improve the image quality of digital cameras. In this work, we studied the stability of NIR absorbing films made of NIR absorbing dyes by varying the kind of transparent polymeric binders, which have different thermal stability. We analyzed the optical properties, thermal stability, and microscopic morphology of the NIR absorbing films and investigated the change of these properties by the heat. The NIR absorbing films using dithiolene dye showed good thermal stability. The diimmonium dyes showed discoloration and decomposition in the films using binders with low thermal stability because of the change of molecular arising from the dissociation of counter anions arrangement. Consequently, we could improve the stability of diimmonium dye-based NIR absorbing films by applying thermally stable binders to the NIR absorbing films. [Display omitted] •Near-infrared (NIR) absorbing films using NIR absorbing dyes and transparent polymeric binders were fabricated.•The change of properties of the NIR absorbing films by the heat was investigated.•The NIR absorbing films using diimmonium dyes and binders with low thermal stability showed discoloration.•The stability of the diimmonium dye-based NIR absorbing films was improved by applying thermally stable binders.