In nature, most of the metallic conducting materials are known to be transparent, and photo-activated to create heat, therefore acting as a photon-to-heat converter. The photothermal effect has been extensively studied for gold and other metallic materials and attributed the energy conversion to the localized surface plasmon resonance (LSPR). A localized plasmon is the result of the confinement of a surface plasmon in a nanoparticle smaller than the wavelength of the incident light. However, for many energy-related applications, it is required to have the base materials highly transparent for efficient collection of photos, for instance, natural sunlight. But the LSPR effect has been previously demonstrated for both noble metals and conducting metal oxides (CMOs) with significant charge carrier densities (n ≈ 1021 - 1023 electrons/cm3 ). As is also well-known, most of the transparent materials (such as silica) are neither conducting nor photo-thermal active. It is, therefore, important to seek for highly transparent photothermal materials for the energy applications that rely on photon source. Chlorophyll has been found to be a highly transparent material that exhibits strong photothermal effect. The molecular structure of chlorophyll (chlorophyll a) consists of a chlorin ring, whose four nitrogen atoms surround a central magnesium atom, and has several other attached side chains and a hydrocarbon tail. Chlorophyll features a saddle-like spectrum with two peaks respectively at 400 nm (blue-violet) and 700 nm (NIR), which is responsible for its transparency. In this study, we report the synthesis and processing of chlorophyll-based thin films. The as-processed chlorophyll thin films can be made in multi-layers and exhibiting high transparency and the photothermal effects for both energy and medical applications. The fundamental operating mechanism of photothermal heating of chlorophyll is identified.
Audience Take Away:
- The audience will learn a new “green material” for energy and medical applications. A new photothermal mechanism will be identified for chlorophyll.
- The green materials synthesis will have profound impact in materials science and enginerring for a wide spectrum of applications. The knowledge learned from this presentation will provide them with new information for frontier technology jobs. Once presented, there will be expected many research groups to be following the new synthesis routs developed by our group. The transparent thin films will have direct applications for energy efficiency and photothermal cancer therapy. The photothermal thin film will provide new information to assist in a design problem. For instance, the thin film will be deposited with multi-layers that can control the heat conversion and light transmittance, those are key design parameters.