Atomistic Band Gap Engineering in Donor–Acceptor Polymers

Citations Over TimeTop 1% of 2011 papers

Abstract

We have synthesized a series of cyclopentadithiophene-benzochalcogenodiazole donor-acceptor (D-A) copolymers, wherein a single atom in the benzochalcogenodiazole unit is varied from sulfur to selenium to tellurium, which allows us to explicitly study sulfur to selenium to tellurium substitution in D-A copolymers for the first time. The synthesis of S- and Se-containing polymers is straightforward; however, Te-containing polymers must be prepared by postpolymerization single atom substitution. All of the polymers have the representative dual-band optical absorption profile, consisting of both a low- and high-energy optical transition. Optical spectroscopy reveals that heavy atom substitution leads to a red-shift in the low-energy transition, while the high-energy band remains relatively constant in energy. The red-shift in the low-energy transition leads to optical band gap values of 1.59, 1.46, and 1.06 eV for the S-, Se-, and Te-containing polymers, respectively. Additionally, the strength of the low-energy band decreases, while the high-energy band remains constant. These trends cannot be explained by the present D and A theory where optical properties are governed exclusively by the strength of D and A units. A series of optical spectroscopy experiments, solvatochromism studies, density functional theory (DFT) calculations, and time-dependent DFT calculations are used to understand these trends. The red-shift in low-energy absorption is likely due to both a decrease in ionization potential and an increase in bond length and decrease in acceptor aromaticity. The loss of intensity of the low-energy band is likely the result of a loss of electronegativity and the acceptor unit's ability to separate charge. Overall, in addition to the established theory that difference in electron density of the D and A units controls the band gap, single atom substitution at key positions can be used to control the band gap of D-A copolymers.

Related Papers

• → Incorporating an Alternating Donor–Acceptor Structure into a Ladder Polymer Backbone(2016)56 cited
• → Synthesis, Fluorescence Properties, and Head-to-Tail Regioselectivity in the Photodimerization of a Donor–Acceptor-Substituted Anthracene(1999)22 cited
• → Optical studies on the intramolecular charge transfer properties of conjugated bridged donor-acceptor supermolecules(1991)3 cited
• → Density Functional Theory Calculation of Band Gap of Iron (II) disulfide and Tellurium(2017)
• → ChemInform Abstract: Synthesis, Fluorescence Properties, and Head‐to‐Tail Regioselectivity in the Photodimerization of a Donor—Acceptor‐Substituted Anthracene.(1999)