Alternating Binaphthyl−Thiophene Copolymers: Synthesis, Spectroscopy, and Photophysics and Their Relevance to the Question of Energy Migration versus Conformational Relaxation

• Published in: Macromolecules Vol. 42; no. 5; pp. 1710 - 1719
• Main Authors: Pina, J, Seixas de Melo, J, Burrows, H. D, Maçanita, A. L, Galbrecht, F, Bünnagel, T, Scherf, U
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.03.2009
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Stille coupling; Chemical solution; Solution polycondensation; Temperature effect; Fluorescence; Arylene copolymer; Thiophene copolymer; Experimental study; Quantum yield; Naphthalene derivatives; Luminescence decay; Solid state; Conjugated copolymer; Anisotropy; Optical properties; Preparation; Aromatic copolymer; Triplet triplet transition; Optical absorption
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma802395c

The synthesis and a comprehensive spectroscopic and photophysical study are presented of four alternating binaphthyl−oligothiophene copolymers (DP: 10−15 repeat units) in solution at room and low temperature and in the solid state (thin films). Detailed results are presented on absorption, emission, and triplet−triplet absorption spectra together with all relevant quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation), excited-state lifetimes, and singlet and triplet energies. From these, several conclusions can be drawn. First, the main deactivation channels for the molecules in solution are the radiationless processes (S1 → S0 internal conversion and S1 → T1 intersystem crossing). Second, in the solid state the fluorescence quantum yields are smaller than those in solution. From time-resolved fluorescence decays in the picosecond time domain, three decay components are seen: a fast decay (40−60 ps) at short wavelengths, which becomes a rising component at longer wavelengths, an intermediate decay component (330−477 ps) associated with an ensemble of isolated segment-like units, which is dominant at the initial part of the emissive spectra and progressively decreases for longer emissions, and a third exponential related to the emission of the fully relaxed polymer. Together with steady-state anisotropy studies, this is discussed in terms of the possibilities of energy migration/transfer along the polymer chain and of the conformational (torsional) relaxation of the systems studied.