​Pressure induced drastic modulation of optical properties in DPFO - Dr. Haiyan Zheng and Junjie Guan

JUNE 12, 2019 

New work from a team of scientists co-led by Dr. Haiyan Zheng from HPSTAR found pressure induced tremendous modulation of the optical properties of an organic molecular crystal (DPFO). Their study shows that DPFO may have potential in the molecular switch applications of modulating photoluminescence under high pressure. Their work is published in recent Materials Chemistry Frontiers.

Diphenylfluorenone (DPFO) is an organic light emitting material, exhibiting brilliant optical properties. There are two forms of DPFO based on different operation conditions such as temperature or solvents, which show distinct optical properties— linear or nonlinear light response.

What about DPFO behaves under high pressure is the focus of current research. High-pressure has been proven to be an effective method to modulate the optical properties of organic materials by changing the molecular arrangements. So the team of scientists aims to use high-pressure to tune the structure and performance of DPFO.

They used multiple of high-pressure techniques to probe how pressure works on DPFO. They found that the yellow DPFO crystal changed to pale red around 3 GPa, and finally to dark red at 7 GPa, which accompanied with a large and continuous redshift of the Uv-vis absorption and photoluminescence across the entire visible light region.

Their further in-situ IR and X-ray diffraction measurement revealed that these color and optical variations are attributed to a crystal structural change at the corresponding pressures. The new structure they found in this study is called gama phase, which contains strong aromatic interactions and promote the formation of long-wavelength absorption and emission.

"Our results indicate that the clear relationship between the high pressure crystal structure of DPFO and corresponding optical properties will contribute to researching the conformation, structure and luminescence characteristics of organic optical materials.”said Dr. Haiyan Zheng.

Caption: The relationship between the optical properties and the crystal structures of the DPFO crystals under high pressure.

二苯基芴酮（DPFO）是一种有机发光材料，具有优异的光学性能。北京高压科学研究中心的郑海燕研究员合作带领的研究团队使用高压来调节DPFO的光学性能，他们发现DPFO在高压下由淡黄色变为淡红色，最终变为深红色。并且颜色的变化伴随着在整个可见光区域的紫外—可见吸收和光致发光的大范围连续红移。他们进一步的高压红外及X衍射数据表明这些变化是由于DPFO在对应压力下晶体结构的改变。新的晶体结构含有强烈的分子间芳香相互作用，促使长波长吸收和发射的形成。