2,3,7,8,12,13-hexaaryltruxenes: An ortho-substituted multiarm design and microwave-accelerated synthesis toward starburst macromolecular materials with well-defined π delocalization

We present herein a novel design and the efficient synthesis towards a "homogeneous" starburst fluorene system based on the novel 2,3,7,8,12,13-hexaaryltruxene scaffold. Controlled microwave heating provides a facile and powerful approach for each step in the synthesis of these bulky materials with large steric hindrance, suggesting an avenue to access structurally well-defined complex organic semiconductors (OSCs) rapidly and conveniently with high yield and purity. The resulting materials exhibited good thermal stability and an excellent glassy structure as revealed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as wide-angle X-ray diffraction (WAXD) studies. Moreover, compared with their corresponding three-arm-substituted counterparts T1-T4, the introduction of the ortho substituents around the truxene core in Tr1-Tr4 results in significant blueshifts (of 7-24 nm) of the absorption maxima λ_max and higher energy optical gaps (E_g). Comparative studies with corresponding linear, rod-shaped oligofluorene counterparts (OFX) have revealed that the longest para-conjugated segment in the TrX (X = 1-4) structures plays the dominant role in determining their electronic properties. UV/Vis data and cyclic voltammetry (CV) investigations have indicated that there is little electronic interaction between the arms, even for the shortest armed oligomer Tr1. A clear linear relationship of both 1/λ_max and E_g with the inverse of (n+1) for these branched systems was found. Our findings highlight a novel molecular design comprising an ortho-substituted, multiarmed architecture that would allow the introduction of isotropic physical and/or mechanical properties, while at the same time maintaining most of the important electronic properties of the rod-shaped constituents of a fully conjugated system.