Abstract
Abstract A homologous series of metathetically synthesized, monodisperse all- trans oligomers of 2,5-diheptyloxy- p -divinylbenzene 1 (DHepO-OPV n s, with n the number of aromatic rings) is characterized for n =1–7. Experiments were carried out in solution at ambient temperature, under matrix-isolated conditions (dispersed in a 2-methyltetrahydrofuran (2MeTHF) glass) at low temperatures (10 and 80 K) and as spin coated thin layers on quartz substrates at various temperatures. The investigations involve absorption and emission as well as site-selective fluorescence (SSF) spectroscopy. DHepO-OPV n s ( n ⩾2) form nanoaggregates and the tendency of the formation increases with increasing concentration and chain length and decreases with increasing temperature. Absorption spectra of isolated chains as well as aggregated species are simulated and agree nicely with the experimental data. Furthermore, the absorption spectra of the aggregates can be correlated with the spectra of the corresponding spin coated oligomer on a quartz substrate. The singlet (S 1 ←S 0 ) transition energies decrease with increasing conjugation length and converge for the longer oligomers towards a limiting value. The Huang–Rhys parameter S associated with the S 1 →S 0 electronic transition and its evolution with conjugation length has been determined via analysis of the vibronic fine structure. At low temperatures, the values determined can be attributed to aggregate formation. At ambient temperature, S decreases with increasing chain length. Low-temperature SSF spectroscopy is employed to study morphological effects on the conformation of DHepO-OPV3. A vanishing Stokes shift is recorded for the resonantly excited fluorescence spectra.
Published Version
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