Design, characterization, optical and photophysical properties of novel thiophene monomers and polymers containing pyrene moieties linked via rigid and flexible spacers

Abstract

Herein, we report the synthesis of three novel thiophene monomers connected to pyrene moieties via a flexible oligo(ethylene glycol) (OEG) spacer with an oxygen -to-pyrene (T1), a flexible OEG spacer with an oxygen -to-pyrene (T2), and a rigid acetylene spacer (T3). These monomers were prepared in an easy manner from commercially available 3-bromo-4-methylthiophene and further characterized by NMR spectroscopy and mass spectrometry. Monomer T2 exhibited the absorption band at 344 nm and a strong “monomer” emission band at 375 nm typical of a 1-pyrenemethyl derivative. Moreover, T1 and T3 showed red shifted absorption bands at 352 and 384 nm arising from the pyrene substituents, namely the electron-donating oxygen to-pyrene and the extended conjugation length, respectively. These compounds exhibited a broad “monomer” emission band between 360~480 nm without excimers. Homopolymers (OHP1, OHP2, and OHP3) obtained from these monomers were partially soluble and their photophysical properties such as quantum yield and lifetime were characterized. Emission spectra of the oligomers OHP1 and OHP3 exhibited an emission band at ~500 nm, which is due to the conjugated polythiophene backbone and does not arise from intramolecular pyrene-pyrene interactions.