Scientist creates a dual-function polymer films that shift colour and store electricity using porphyrin-based molecular design

Sachin Kochrekar, a PhD student at University of Turku, Finland

PhD researcher develops dual-function polymer films for energy systems
Porphyrin-based materials combine electrochromic switching with electrical energy storage
Nickel, zinc, and metal-free films show different optical behaviours

A PhD researcher at the University of Turku has developed multifunctional materials that could eventually be used in smart windows capable of storing energy while adjusting indoor light levels.

The work focused on porphyrins, naturally occurring molecules found in biological systems such as chlorophyll and hemoglobin.

These molecules are known for their ability to participate in energy transfer and other important chemical processes.

Nature-inspired materials combine two functions

The polymer films developed in the work combine electrochromic behavior with electrical energy storage in a single material.

In this system, electrochromic materials change color when electricity is applied, while energy-storage materials capture and release electrical charge.

Combining both functions could broaden the use of smart surfaces in energy-efficient technologies and other applications.

Doctoral researcher Sachin Kochrekar said porphyrins provided a useful starting point because of their natural ability to transfer electrons and alter their electronic states under controlled conditions.

“For example, thanks to the porphyrin structure found in chlorophyll, the plant is able to recover energy from sunlight through photosynthesis,” said Sachin Kochrekar.

“The ability of this natural molecule to transfer electrons and change its state in a controlled manner is also an interesting starting point for us materials scientists.”

The study uses two different approaches — one method combined porphyrins with electrically conductive compounds.

The other method connects porphyrins through molecular bridge structures to form polymer membranes without requiring specially modified starting materials.

Both methods resulted in polymer membranes that exhibit combined electrochromic and energy-storage properties, although their performance depends on the synthesis route.

Small structural changes produced different results

The study also examined how altering the central component of the porphyrin structure affected material performance.

It incorporated nickel, zinc, or no metal at all into the molecular framework and observed notable differences in behavior.

Results showed that the nickel-containing film could reversibly switch among three distinct colors, while zinc-containing and metal-free versions transitioned between two states.

The color changes occurred rapidly, generally within two seconds, while the materials maintained strong visual contrast during operation.

The films retained their coloration after electrical power was removed, a characteristic that could reduce energy consumption in practical applications where continuous power is undesirable.

Beyond color-changing behavior, the materials were evaluated as electrochromic supercapacitors using water-based electrolytes.

Such systems are generally considered safer and environmentally preferable than many conventional electrolyte technologies.

The experimental films demonstrated measurable energy-storage capabilities and maintained performance across thousands of charging and discharging cycles.

According to the University of Turku, this is the first study of these specific porphyrin-based polymer films operating as electrochromic supercapacitors within an aqueous electrolyte environment.

Smart windows remain a future possibility

There are several potential applications of this study, and the relatively low cost of producing the materials makes them relevant for further evaluation.

“The materials are low-cost to produce, easy to control and highly adaptable and can be integrated into a wide range of applications, including flexible and stretchy substrates,” Kochrekar said

“In the future, these materials could be used, for example, in sensor technology, flexible electronics, smart clothing and solar energy solutions.”

One potential application involves window systems capable of adjusting transparency while simultaneously storing solar energy collected throughout the day.

“For example, new types of smart windows could simultaneously store solar energy and darken in the bright sun, which would reduce the need for cooling in the building.”

However, the research remains at the materials-development stage, and further engineering work would be required before it can appear in commercial buildings or consumer products.