Oligo(isobenzofuran): A Computational Study

Organic electronic materials have unique optical and electronic properties, and therefore find many applications such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and more. Additional important application is organic photovoltaics, which require low band gap for efficient exploitation of the solar spectrum in the Near-IR spectral range. In order to achieve low band gap π conjugated molecules, and especially those with strong quinoid character, are needed. Today, polythiophene-based materials are widely studied and used, but their band gap is not suitable for the Near-IR. Oligo(isobenzofuran) are an interesting derivative of oligo-thiophene. Their electronic structure is similar to thiophene but many other properties (such as stronger quinoid character and higher HOMO) are more suitable for absorption at the Near-IR.^[1,2]

In this work, we present a computational (DFT) study of oligo(isobenzofuran) bearing different substituents. In particular we inspected features such as geometries, HOMO and LUMO levels, and optical properties. The results show that oligo(isobenzofuran) are more planar, display a significant quinoid character, and lower HOMO-LUMO gaps compared with their thiophene analogs. Substituents on the phenyl moiety and on α positions significantly lower the HOMO energy and might help stabilize the molecule.

Figure. Calculated structures (DFT/B3LYP/6-311G(d)) of quater(isobenzofuran) (left) and quater(isobenzothiophene) (right).

[1] T. M. Swager, Macromolecules, 2017, 50, 4867-4886.

[2] Dou, L.; Liu, Y.; Hong, Z.; Li, G.; Yang, Y., Low-Bandgap Near-IR Conjugated Polymers/Molecules for Organic Electronics. Chem. Rev. 2015, 115 (23), 12633-12665.