Synthesis And Properties Of TTF-Fluorene Polymers

Polymers containing tetrathiafulvalene (TTF) moiety have attracted much interesting in the field of organic semiconductors and organic conductors in the recent years. Meanwhile, fluorene polymers have been extensively applied as light-emitting materials, nonlinear optical materials and fluorescence sensors, due to their excellent electrochemical and spectroscopic properties. The present paper focused on the design and synthesis of TTF-Fluorene polymers, as follows:Two TTF-Fluorene triads (TTF-Fluorene 1-2) with fluorene, TTF and ethynylbenzene unit were designed and synthesized using Sonogashira coupling reaction. The reaction mechanisms and the factors of affecting on reactions were discussed. The results indicated that the incorporation of the donor TTF unit hindered Sonogashira coupling reaction between 2,7-dibromofluorene and ethynylbenzene, therefore, introducing ethynylbenzene unit to the fluorene before TTF unit was a better way to obtain TTF-Fluorene triads. The absorption spectra, fluorescence spectra and cyclic voltammetry (CV) of these two triads were measured. The CV and absorption spectra indicated that the intramolecular interaction occurred between the TTF and fluorene moieties in TTF-Fluorene 1-2 in the ground state. The fluorescence spectra indicated the intramolecular energy transfer and intramolecular interaction existed in the excited state, which made the quench of fluorescence of TTF-Fluorene 1-2.TTF-Fluorene polymers (PEFT 1-3) with ethynyl unit in the main chain were synthesized via prepolymerization and postpolymerization methods using Sonogashira coupling reaction respectively. The structures of these polymers were characterized by 1H-NMR and the properties were researched by absorption spectra, fluorescence spectra, CV and conducting tests. The functionalization of PEFT(pre) and PEFT(post) were 40% and 100% respectively, indicating that postpolymerization method was better than prepolymerization to obtain TTF-Fluorene polymers. Absorption spectra, fluorescence spectra and CV revealed that intramolecular interaction existed between TTF moiety and fluorene polymer backbone in the ground state and photo induced electron transfer reaction (PET) occurred from the TTF moiety to the fluorene polymer backbone in the excited state. Besides, stereospecific hinder also could be found between the TTF and fluorene polymer backbone. The functionalization of TTF affected the interactions. With the increasing ratio of TTF unit in the side chain, these reactions enhanced. However, different backbone in PEFT 1-3 had small effect on these intramolecular interactions.A TTF-Fluorene oligomer (OFT) was synthesized by the Yamamoto coupling reaction from TTF-Fluorene 3 using Ni(COD)2 as catalyst. The fluorescence spectra of OFT displayed weak fluorescence intensity because of the PET reaction and energy transfer between the TTF and fluorene oligomer backbone, while the fluorescence intensity would enhance significantly after chemical oxidation. The absorption spectra and CV showed that an intramoleular interaction existed between the TTF and fluorene backbone in OFT, while in model molecule TTF-Fluorene 4 such interaction could not be observed, due to the chain propagation of the fluorene backbone and an enhanced internal charge transfer interaction between the two electroactive moieties.The postpolymerization methodology could be applied to synthesize TTF-Carbazole (PECT 1-3). CV and absorption spectra showed that an intramoleular interaction existed between TTF and polyethynylcarbazole. A strong fluorescence quench (c.a 99%) could be observed, compared to the PEC without TTF units, which could be ascribed to the PET interaction from TTF moiety to the polyethynylenecarbazole backbone. The observed onset decomposition temperatures (Td) for PECT 1-3 were 260,256 and 298℃respectively.The doped PEFT 1-3, OFT and PECT 1-3 exhibited good thermal properties and higher conductivity (PEFT 1-3,-1-3x10-3 S·cm-1; OFT,1.4×10-3 S·cm-1; PECT 1-3,-6-11×10-4 S·cm-1) and could be used as potential organic conducting polymers.