Figure: A general schematic showing how the geometry of two connected NIR absorbing molecules dictates the energy of radiation absorbed; low energy (red) for the head-to-tail arrangement and high energy (blue) for the parallel arrangement.

Tuning low energy absorption via excited state interactions

The motivation – In the world of advanced chemical materials, those that absorb near infrared (NIR) light have a variety of interesting applications in wireless communication, bio-imaging, sensing, and optics. As a practical example, NIR absorbing materials are often applied to the surface of plasma television screens to reduce the transmittance of NIR radiation, which may cause malfunction of remote controls. The majority of molecules absorb light in the visible and/or ultraviolet range, which precludes a selective response to light activation This study aimed to develop a series of NIR absorbing materials and investigate the mechanism that determines the energy of NIR radiation absorbed.

The discovery – The research groups of Tim Storr and Loren Kaake at Simon Fraser University, along with Fabrice Thomas (Université Grenoble-Alpes), discovered that when two NIR absorbing molecules are connected in close proximity, the energy of absorbed NIR radiation is dependent on the relative orientation of the individual molecules.

Its significance – This work is significant as it provides a mechanism to develop materials that selectively absorb specific NIR radiation energies. This will be of interest for the development of sensor technology, and also the telecommunications industry where fiber-optic transmission relies on wavelengths in the NIR region. In addition, molecules that absorb a greater fraction of the solar spectrum, especially in the NIR, could be used to boost the power conversion efficiency of solar cells.   

Read the paper“Exploiting exciton coupling of ligand radical intervalence charge transfer transitions to tune NIR absorption” by Clarke, RM; Jeen, T; Rigo, S; Thompson, JR; Kaake, LG; Thomas, F; Storr, T. Chemical Science 9(6):1610-1620 (2018). DOI: 10.1039/c7sc04537a

Website article compiled by Jacqueline Watson with Theresa Kitos