(576h) In silico Exploration of Polyimides with High Index of Refraction Using Molecular Modeling and High-Throughput Screening

In silico exploration of polyimides with high index of refraction using
molecular modeling and high-throughput screening

Mohammad Atif Faiz Afzal¹,
Chong Cheng¹, Johannes Hachmann¹

¹Department
of Chemical and Biological Engineering, University at Buffalo, Buffalo, New
York, United States

Abstract

Organics polymers are emerging materials in
various optical and optoelectronic applications due to their superior
properties over conventional inorganic materials. The critical property
necessary in such applications is the high refractive index (RI) of the
material, but typical carbon based polymers have low RI values which limit
their use.¹ Thus, organic polymers with higher RI values, typically
greater than 1.8, have attracted considerable interest in recent years. An important
advantage of organic materials is that their properties can be tuned readily
and significantly by controlling their molecular structure. According to
the Lorentz-Lorenz equation, the incorporation of substituents with a high
molar refractivity and low molar volume can increase the RI values of these
materials. This further suggests that the ability to
tailor the molecular structure of polymers is the key to increasing their RI
values. But, tailoring the structure using different functional groups could
potentially lead to an infinite number of molecular candidates. It is
impractical to empirically characterize a large number of candidates, whereas
computational analysis allows greater exploration at a mere fraction of the
time and cost.

We developed an RI prediction model based on the first-principles
calculations and data modeling, and validated the model using experimental RI
values of 112 polymers (R²=0.94).² We cast this model in our
rational design framework to identify polyimides (PIs) with high RI values. In recent years, PIs have been shown to have favorable
thermal and mechanical properties, making them excellent candidates for various
applications. However, the optical properties of PIs are significantly inferior
compared to conventional metal oxides that are currently used in optical and
optoelectronic devices. Tailoring the chemical structure of PIs can allow for
precise tuning of the optical properties, in particular, to increase their RI
values. We created a molecular library of 270,000 PIs from promising building
blocks, suggested by our experimental collaborators. We identified the best
candidates by screening the library using our virtual high-throughput screening
framework. The screening study resulted in more than 2000 PIs with RI values
greater than 1.8. In addition to identifying
high RI candidates, we applied materials informatics and data mining techniques
to understand the relationship between the molecular structure and the RI
values. Using these techniques, we identified building blocks and combinations
of building blocks that are prominent in the top RI candidates. We demonstrate
that the developed rational design framework is a powerful tool and has shown
to be highly promising for rapidly identifying polymer candidates with
exceptional RI values as well as discovering design rules for advanced
materials.

References:

1. Liu, J. G.; Ueda,
M., High refractive index polymers: fundamental research and practical
applications. Journal of Materials Chemistry 2009, 19
(47).

2.
Afzal, M. A. F.; Cheng, C.; Hachmann, J., Combining first-principles and data
modeling for the accurate prediction of the refractive index of organic
polymers. The Journal of Chemical Physics 2018, 148 (24).