Optical brighteners are a class of fluorescent materials that absorb light in the ultraviolet regions of the electromagnetic spectrum (e.g., less than 400 nm) and re-emit light in the violet and blue regions of the electromagnetic spectrum (e.g., greater than 400 nm). Optical brighteners are used in a variety of applications to enhance the color or appearance of materials, such as paper and fabrics. Generally, optical brighteners are used to increase the perceived whiteness of such materials by increasing the overall amount of blue light emanating from the material (i.e., reflected from the material and emitted by substances deposited on the material).
While optical brighteners have been used to treat a variety of materials, some commercially-available optical brighteners have proven difficult to effectively deposit on certain substrates. For example, some commercially-available optical brighteners do not effectively deposit onto polyester-based fabrics. When such optical brighteners are used in laundry care compositions, polyester-based fabrics treated with the compositions typically show no deposition of the optical brightener and, consequently, no improvement in their whiteness index.
Accordingly, a need still remains for optical brighteners that exhibit effective whitening on a variety of substrates and for compositions (e.g., laundry care compositions) comprising such optical brighteners. This application seeks to provide such optical brighteners.