Kindai University successfully measures circularly polarized luminescence in high-pressure environment

A research group led by Professor Yoshitane Imai and Associate Professor Mizuki Kitamatsu from the Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, along with Satoko Suzuki from JASCO Corporation, successfully achieved the world's first measurement of circularly polarized luminescence under high-pressure conditions at a hydrostatic pressure of 100 MPa. While circularly polarized luminescence is known to change according to environmental conditions such as temperature and solvents, research using high-pressure environments had been uncharted territory. This achievement enables the construction of a new platform for controlling and evaluating optical activity in solutions through pressure. Expected applications include sensor technology in extreme environments, pressure-responsive displays and authentication, optical technology for detecting environmental changes, and next-generation optical communications technology. The results were published online in Chemistry Letters.

Light that vibrates in a specific direction is called polarized light. Circularly polarized light is a special type of light that rotates in a helical pattern, and there are expectations for its application in next-generation sensing and optical communications technologies. Circularly polarized luminescence arises from optically active materials, and its characteristics are influenced by environmental conditions such as temperature and solvents.

Pressure significantly affects the electronic states and molecular arrangements of materials, potentially enabling the discovery of new characteristics and principles of circularly polarized luminescence under special pressure conditions. Measuring circularly polarized luminescence under high pressure is important for understanding how external environments change the electronic states and luminescence mechanisms of materials. However, research on circularly polarized luminescence utilizing the extreme environment of high pressure in solutions had not previously been conducted.

The research group synthesized a total of eight types (DD/LL) of chiral oligopeptides as luminescent materials by introducing two pyrene rings with gradually varied spacing between them. Using these in dichloromethane solutions, they measured photoluminescence (PL) and circularly polarized luminescence (CPL) under high-pressure conditions at a hydrostatic pressure of 100 MPa. The measurements utilized a high-pressure CPL measurement system combining a YAG window high-pressure cell and a CPL-300 circularly polarized luminescence measurement system.

Under atmospheric pressure, they observed monomer-derived PL (379-396 nm) as well as excimer-derived PL (460-470 nm) and excimer-derived CPL (461-469 nm), showing their mirror-image relationship. Furthermore, they successfully achieved clear detection of excimer-derived CPL (461-485 nm) even under high pressure at 100 MPa.

When conditions changed from atmospheric to high pressure, a slight red shift was observed where the wavelength of excimer-derived CPL shifted slightly toward longer wavelengths. Additionally, the CPL intensity decreased according to the excimer PL intensity ratio, indicating that pressure altered the stacking structure of the pyrene rings, partially disrupting the arrangement necessary for luminescence.

This demonstrated for the first time a versatile platform capable of controlling and evaluating chirality in photoexcited states in solutions through the external factor of pressure.

Future applications are expected in controlling luminescence characteristics through pressure, discovering new luminescence principles, and next-generation optical sensor and optical communications technologies.

Imai commented: "Through these achievements, we were able to directly capture the 'chirality of excited states in extreme environments,' which had been difficult to observe previously. Quantitative response analysis using pressure represents a major step toward extreme environment sensing and the design of pressure-driven optical functions."

Journal Information
Publication: Chemistry Letters
Title: Circularly polarized luminescence from bipyrenyl peptides under high pressure
DOI: 10.1093/chemle/upaf170