We have studied the interplay between photophysics and film morphology of poly(9,9-dioctyl)fluorene (PFO) using a variety of optical probes. Upon slowly warming a spin-cast PFO film from 80 to 300 K, a fraction of the sample is transformed into a different solid phase, the $\beta$ phase. Absorption and electroabsorption measurements show that the $\beta$ phase has more extended conjugation than the glassy phase. As a consequence, excited states of the $\beta$ phase are redshifted and have higher polarizability. The photoinduced absorption spectrum of a glassy PFO film is dominated by triplet excitons, whereas both polarons and triplet excitons are seen in a sample containing a fraction of the $\beta$ phase. The dependence of the photoinduced absorption and photocurrent upon the excitation wavelength shows that there is a clear link between polaron and triplet photogeneration.

The synthesis of a new soluble conjugated porphyrin polymer 4 is reported. The MALDI TOF mass spectrum shows the presence of oligomers with up to 13 repeat units and GPC gives a M_n of 53 kDa. The electronic absorption spectra of this polymer exhibit an intense Q band at 800 nm in solution and 853 nm in the solid state, demonstrating a high degree of conjugation. Electroabsorption spectroscopy shows that thin films of 4 have lower resonant third order NLO susceptibility than our previous conjugated porphyrin polymer 2, whereas closed z-scan measurements indicate that the off-resonance real susceptibility, at 1064 nm, is exceptionally large for both polymers (χ⁽³⁾ _R = −2 × 10⁻¹⁶ m² V⁻²). Open z-scan measurements were also made at 1064 nm, demonstrating that the two polymers exhibit similar nonlinear absorption at this wavelength (β = 1 cm GW⁻¹ at 0.2 mM concentration).

Organic electroluminescent devices (OEDs) emit light when an electric current is applied to a thin film section. They arise from two main technology branches—small molecules and light emitting polymers. Apart from the insight offered into the fundamentals of their physics, which is relevant to topics such as electrical transport in biological systems and molecular computers, understanding how the mobilities in these system sv ary with morphology and composition enables the design of improved materials for technological requirements, e.g. fast switching speeds for active matrix displays and polymer field effect transistors. In this review, we have focusse do n the m odels of transport in OEDs that address the unusual nature of this transport and underpin device design. The review concludes with the following point: as new materials for use in OEDs continue to appear, modelling is essential for the prediction of their transport properties, which in turn leads to the establishment of fundamental trends in the behaviour of devices employing them.

We have used absorption and electroabsorption spectroscopy to investigate the electronic structure of poly(para-phenylene vinylene) (PPV) and poly (2-methoxy, 5-${(2\mathrm{}}^{\prime }$-(ethyl)hexyloxy)-p-phenylene vinylene) (MEH-PPV). In particular we examine the often used assumption that the electronic structure of PPV and its dialkoxy substituted derivatives are essentially the same. The absorption spectrum of PPV consists of three peaks, while that of MEH-PPV has four peaks. We discuss the controversial origin of the extra peak as well as evidence for Davydov splitting effects in the absorption spectrum of PPV. The analysis of the nonlinear spectra shows further differences between the two materials. First, the binding energy of the ${1B}_u$ exciton for PPV is some 0.1 eV higher than for MEH-PPV. Second, the peak value of $\mathrm{Im}\{{\chi }^{\mathrm{}\left(3\right)\mathrm{}}(-\omega ;0,0,\omega )\}$ for PPV is approximately 40 times higher than that of MEH-PPV. We also found that the sum-over-states modeling of the electroabsorption spectra indicates that the transition dipole moment between the ${\mathrm{mA}}_g$ and ${\mathrm{nB}}_u$ states is of opposite sign in the two polymers.