The UV/vis spectra were measured with a JASCO V-550 UV-Vis spectrophotometer, the emission spectra with a CARY Eclipse fluorescence spectrophotometer. IR spectra were recorded on a JASCO FT/IR-4200 Fourier Transform spectrometer. NMR spectra ( 1 H and 13 C) were measured with a Bruker ARX 400 spectrometer using solutions in CDCl 3 ; J values are given in Hz. Mass spectra were obtained using a Varian MAT 311A instrument with an electro spray ionization source (ESIMS). The microwave-assisted synthesis was carried out in a Discover reaction unit (CEM) using sealed reaction vials. The temperature inside the vial was monitored by an IR sensor; the pressure by a hydraulic system. The polymerizations were performed under temperature control with a maximum microwave power of 300 W. MaterialsAll reactions were carried out under an argon atmosphere using the usual Schlenk techniques.TLC was carried out on dry silica gel plates. For liquid chromatography, silica gel with a pore size 0.06-0.2 nm was used. All solvents were of reagent grade and used as received, unless otherwise specified. 5,8-Dibromo-2,3-dioctylquinoxaline, 1 4,4-bis(2-ethylhexyl)-2,6bis(trimethylstannyl)-4H-cyclopenta- [2,1-b:3,4-b`]dithiophene 2-4 , 2-(tri-n-butylstannyl)thiophene, 5 and 4,7-dibromobenzo-2,1,3-thiadiazole 6 were prepared according to literature procedures. Synthesis 4,7-Bis(thiophen-2-yl)benzo-2,1,3-thiadiazole 4,7-Dibromobenzo-2,1,3-thiadiazole (17.01 mmol, 5 g), 2-(tri-n-butylstannyl)thiophene (37.4 mmol, 13.96 g), KF (136 mmol, 7.91 g) and PdCl 2 (PPh 3 ) 2 (1.36 mmol, 0.955 g) were placed in a 100 ml-Schlenk tube. After addition of dry THF (100 ml) the reaction mixture was stirred for 48 h at 80 °C. Then, the reaction mixture was poured into chloroform (200 ml). The organic phase was washed with water (2 × 200 ml), dried over anhydrous MgSO 4 and the solvent removed under reduced pressure. Purification by column chromatography (silica gel, toluene/n-hexane 1/4 v/v) gave 2.19 g (7.29 mmol; 42.9 %) of red crystals.

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 (S 1 f S 0 internal conversion and S 1 f T 1 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.

The optical and electronic properties of novel, alternating quinoxaline/oligothiophene donor-acceptor copolymers show an unexpected independence of absorption and photoluminescence, as well as of the HOMO/LUMO energy levels, on the length of the oligothiophene segments in the copolymer main chain.