The next time you reach for your Transitions® glasses, you can thank Dr. Anil Kumar, an associate fellow in the Optical Division at PPG and the latest recipient of ACS's Award for Creative Invention for his contributions in photochromism and variable polarization and leadership in commercialization.
Kumar grew up in New Delhi and earned a BS and MS from Delhi University. He later transferred to the University of Connecticut, earning a PhD in Organic Chemistry. For his thesis, he studied charge transfer mechanism in photo degradation of some of the medications people take and its role in photo-toxicity and photoallergy. This required him to apply his knowledge of organic chemistry, photochemistry and medicinal chemistry. According to Kumar, “It was something I was very interested in, and something PPG was moving toward with its photochromic research.”
He joined Pittsburgh-based PPG in 1991 to study photodegradation (fatigue) of dyes in photochromic lenses, and help develop “good, stable and high performing” dyes for plastic lenses (this capability was already available in glass lenses).
Photochromism is a photo-induced color change that also reverts back to clear state via thermal or photo process, depending on the type. Photochromic lenses are made primarily of plastic, glass or polycarbonate and are embedded with millions of molecules, including silver chloride or silver halide. The molecules in lenses are transparent and colorless until they are exposed to the ultraviolet rays of sunlight, at which point, they isomerize and change shape to a longer conjugated chromophore, causing the lenses to darken.
In partnership with Transitions Optical (then a joint venture of PPG and French eyewear company, Essilor), the team produced Transitions Plus®, the first commercially successful photochromic plastic lens. The original lens has been followed by several generations of improved products.
Also called adaptive lenses, Transitions® lenses (the most popular brand of photochromic lenses) are transparent indoors and at night and automatically darken outdoors, blocking UV rays and bad blue light, while they help to enhance contrast and reduce glare.
Kumar wanted to develop a version of the lens that would not only darken as conditions change but also polarize in the darkened state. That required a dye that would be clear indoors and dark outdoors, but when dark it orients itself in a fashion that generates polarization in a specific direction. It would also require developing new and scalable production procedures, he says.
The team has continued to innovate with the dyes, materials and processes, launching Transitions Vantage®, the first clear-to-polarized product. In addition to providing protection from bright sunlight, the key advantage with clear-to-polarized lenses is the reduction of blinding glare and light scatter reflecting off surfaces.
In 2014, Essilor acquired the entire stake in Transitions®, however PPG still maintains the R&D function. Kumar’s team continues to innovate to further improve the performance and develop novel dyes and materials that were eventually used in the Transitions® XTRActive Polarized product, introduced in January 2021. The XTRActive Polarized lenses start out as clear indoors and polarize outdoors in the sun with fast-reacting dichroic dyes which achieve up to 90% polarization efficiency.
Each lens starts as a plastic lens substrate, which basically looks like a small, clear hockey puck, and then various layers and coatings are added one after another, some thermal-cured, and some photo-cured. When the “hockey puck” is fully layered, the plastic piece is then ground back using a special milling machine to adjust for a person’s specific prescription and to fit into a frame. The end product weighs about 5%-10% of its original weight, depending on the prescription. Naturally, there are many considerations to getting it just right. “All these layers have to survive that process and maintain their ophthalmic quality with no distortions,” says Kumar. “It also has to be stable for the duration of prescription.”
Unique in the industry, the lenses are also designed to reduce bright light while driving. “The dyes we developed had to work with the smaller amount of high energy visible light coming through the windshield,” Kumar says. “We call this XTRAactive dyes.”
Kumar and his team at PPG continue to develop new materials, dyes and processes to help the huge number of people around the world who need vision correction and want products that also protect their eyes from UV, blue light and outdoor glare. “There are some exciting projects we’re working on now that will hit the market in future,” he hints.
As an Associate Fellow and Senior Researcher, Kumar oversees a scientific team and also gets involved in new partnerships hoping to use the team’s knowledge and expertise in novel applications in the areas, such as security, sensors, displays, switches, windows, etc.
“There are many possible markets for our materials and technologies,” he notes. “As a scientist, I love coming up with new ideas and providing answers to challenging problems that make my creative juices flow.”