Synthesis and Characterization of Monodisperse Oligo(fluorene‐co‐bithiophene)s

Abstract

A series of monodisperse oligo(9,9-di-n-octylfluorene-co-bithiophene)s (OFbTs) with molecular lengths of up to 19.5 nm and molecular weights up to 7025 g mol(-1) has been synthesized by a divergent/convergent approach involving Stille coupling reactions. Stille coupling is quite efficient in preparing this class of oligomers, and even the molecule with nine fluorene units and eight bithiophene units (F9Th16) can be synthesized in a yield as high as 70 %. Because of easy functionalization of the thiophene ring at its alpha position, no additional protecting group allowing activation for further reaction is necessary. However, the synthetic routes must be optimized to eliminate contamination of the targeting compounds with the homocoupling product of the organotin reagents. Synthesis of the longest oligomer F13Th24 in a relative large quantity is limited by its low yield due to the pronounced ligand-exchange side reactions of the starting materials and reaction intermediates. All oligomers longer than F4Th6 are nematic mesomorphs and exhibit enhanced glass transition temperature and clearing point with increasing molecular length, as revealed by differential scanning calorimetry and polarizing optical microscopy. Absorption and photoluminescence (PL) measurements reveal that OFbTs are well-conjugated systems with an effective conjugation length longer than the length of F13Th24.

Phase Transition Behavior and Molecular Orientation of Oligo(9,9′‐dioctylfluorene‐alt‐bithiophene)

“…Recently, we synthesized a series of monodisperse oligo(fluorene-co-bithiophene)s and studied their adsorption and photoluminescence properties. [18] In the current paper, oligo(9,9 0 -dioctylfluorene-alt-bithiophene) (OF8T2, as shown in Figure 1), was chosen as a model for the investigation of the phase transitions of the conjugated oligomer in the bulk, as well as film morphology and molecular orientation in thin films, and it was found that both film thickness and annealing temperature were critical to the formation of ordered structure in the films.…”

Synthesis and Processing of Monodisperse Oligo(fluorene‐co‐bithiophene)s into Oriented Films by Thermal and Solvent Annealing

“…In the absence of chain entanglements and defects, relatively short and uniform chains are also conducive to the formation of monodomain films by monodisperse conjugated oligomers. To take advantage of these favorable material traits, a number of monodisperse oligo(fluorene)s, [31][32][33][34][35][36][37][38][39][40] OFs, and oligo(fluorene-co-bithiophene)s, [41][42][43] OF2Ts, have been reported, but challenges remain in the understanding of how molecular structures affect material properties that are critical to the performance of polarized light-emitting diodes and anisotropic field-effect transistors. Of particular interest is the ability of conjugated oligomers to form glassy liquid crystalline films with elevated phase transition temperatures and superior stability against thermally activated crystallization.…”

X‐ and H‐Shape Two Dimensional Conjugated Oligomers with Anthracene as the Node

“…[23a,c] X0, H0, and X-and H-mers were synthesized by typical Stille cross-coupling reactions. [24] To ensure purity, all of the above oligomers were purified by preparative gel-permeation chromatography (PGPC) after general chromatographic purification on silica gel, and the yields of the oligomers were 30-45 %. Chemical structures of all these compounds were validated by using NMR spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS), and elemental analysis.…”