Predictability of Thermal and Electrical Properties of End-Capped Oligothiophenes by a Simple Bulkiness Parameter

Abstract

The branching topology of end groups attached to several series of oligothiophenes has a systematic effect on thermal and electrical properties of the oligomers. The series were synthesized in a modular approach and show a distinct drop of the melting point T m on increasing bulkiness of the substituents. The same trend can be found for the dissociation temperatures T dis of aggregates in solution. Similarly, monolayer OFET mobilities μ FET are significantly decreasing with increasing bulkiness of the substituents. A simple geometric model is presented quantitatively correlating the transition temperatures and mobilities with the substituents' structure based on a bulkiness parameter P, which allows predicting T m , T dis , and μ FET of corresponding not yet synthesized oligomers with branched substituents. This model might be generally applicable for endcapped rod-like conjugated oligomers.

Effect of Double Branching in α,ω‐Substituted Oligothiophenes on Thermal Solid‐State Properties

“…In contrast, increasing the length of the second linker also leads to an increase in the isotropization temperatures T c , although less pronounced than for the first linker (blue open symbols in Figure 2). [22] This is also supported by the lower transition temperatures of the pre-oligomers RnTdionnTR compared with the fully conjugated oligomers RnTR, because of the non-planar 1,4-diketo moieties and thus disturbed intermolecular π-π interactions of the preoligomers. This means that a closer branch disturbs more efficiently the order of the oligomeric core than a branch further apart.…”

“…Figure 1 shows exemplarily the thermogram of septithiophene R A 7TR A , which will be explored more in detail (see below). This is expected as the additional branching causes an increase in the volume of the branch, and thus the volume ratio v(branch)/v(linker), introduced earlier as the socalled packing parameter P. [22] An increasing P was found to decrease the intermolecular forces and thus to lower, for example, the transition temperatures. [22] Looking at the temperatures T c for the highest thermal transition to the isotropic phase, the two additional dihexyl(methyl)silyl groups in the present substituents cause a lowering of the thermal transition of around 40 K [e.g., T c = 177°C (R′7TR′) and 270°C (R′9TR′) for R′ = C 3 H 6 Si(CH 3 )(C 10 H 21 ) 2 [22] vs. T c = 138°C (R7TR) and 225°C (R9TR) for R E (Figure 2)].…”

“…[21,22] Thiophene was lithiated and alkylated with a bromoalkene and in a hydrosilylation step treated with dichloro(methyl)silane to give 1TnSi (Scheme 2). At first, the various substitution patterns were prepared at a single thiophene unit (Scheme 2) followed by the construction of the oligomers (Scheme 3), similarly to a procedure previously described for oligomers with mono-branched substituents.…”

“…All thermal data are summarized in Table S1 in the Supporting Information. [22] Looking at the temperatures T c for the highest thermal transition to the isotropic phase, the two additional dihexyl(methyl)silyl groups in the present substituents cause a lowering of the thermal transition of around 40 K [e.g., T c = 177°C (R′7TR′) and 270°C (R′9TR′) for R′ = C 3 H 6 Si(CH 3 )(C 10 H 21 ) 2 [22] vs. T c = 138°C (R7TR) and 225°C (R9TR) for R E (Figure 2)]. The behaviour observed is quite similar to the monobranched counterparts with varying positions of the branching point reported earlier.…”

“…In turn, the weakening might have a strong effect the substituents causes surprisingly low overall transition enthalpies and entropies for the oligomers of 10-20 kJ mol -1 and 15-40 J mol -1 K -1 , respectively, whereas the pre-oligomers with interrupted conjugation display values in the range of 15-40 kJ mol -1 and 40-100 J mol -1 K -1 , respectively. [19][20][21][22] The present contribution is a logical extension of the previous reports, with further branching points introduced into the substituents. on solid-state structures and thus electronic properties in (thinfilm) applications.…”