Polythiophenes, and in particular poly(3-hexylthiophene), are used extensively in optoelectric devices. Nonetheless, the factors that influence their emission properties are not well understood. Here we examine the effects of chemical substitution on small oligothiophenes to develop a better understanding of the structure-property relationships for their excited electronic states. We characterize our compounds (Figure 1) using both time-resolved and steady-state optical techniques as well as computational methods. Experiments show that the outer-substituted derivative, 55Br2T, has similar properties to 2T, demonstrating that the electronic effects due to the bromination are minor. However, the inner-substituted derivatives, 33Br2T and 33Me2T, have very different properties from 2T, including much larger Stokes shifts. Perhaps most interestingly, emission arises primarily from excitation in a low-extinction red tail of the absorption spectra not present in 2T. To understand this unusual effect, we model the ground- and excited-state energy surfaces as a function of dihedral angle. Extensions to the long chain limit are planned.

Substituent effects of the properties of short oligothiophenes: A combined physical and theoretical approach

248th National Meeting (2014)

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