Evaluation of Organic EL Materials

Download PDF May 31, 2017

Introduction

EMV-100 Electric Field Modulation Spectrophotometer

EMV-100 Spectrophotometer

Molecular electronic elements using optically functional materials, including organic EL elements and organic optical conversion molecular elements, employ the luminescence accompanying light excitation in an electrical field and are the focus of next-generation display technology instead of LCD’s and plasma displays. Elucidating the electronic structure, molecular structure and molecular alignment of these materials after light excitation in an electric field is extremely important in the development of new materials, such as organic EL elements. Techniques that are known to be effective for evaluating such materials are the change (AU) ∆µ in dipole moment and the change (AU) ∆α in polarizability. ∆ µ and ∆α are extremely important for elucidating the charge transfer in response to the transitions and electrical characteristics of chromophores, respectively.

JASCO developed the EMV-100 Electric Field Absorption Spectra Measurement System to apply an electric field to a sample and then measure the accompanying change in absorbance in the ultraviolet, visible light, and near-infrared regions. The system makes it possible to quantify ∆µ and ∆α, the characteristic parameters of absorption and fluorescence transitions.

Pyrene doped on a PMMA (polymethylmethacrylate)

As examples of the characteristic spectra indicating Stark shift, the figure above shows the absorption spectrum, first derivative of the absorption spectrum and the electrical field absorption spectrum of a pyrene-doped polymethylmethacrylate film. The electric field absorption spectrum has the same waveform as the first derivative of the absorption spectrum and the change in absorption intensity by the electric field suggests that it is due to a change in the molecular polarizability.

About the Author

Leah Pandiscia received her PhD from Drexel University where she studied Biophysical Chemistry. She is a Spectroscopy Applications Scientist at JASCO.