Picosecond fluorescence anisotropy and lifetime measurements are used to investigate the orientational dynamics and steady state order of the fluorescent probe oxazine 4 in the nematic and isotropic phases of 5, 6 and 7 cyanobiphenyl. Variation of the excitation polarisation angle beta with respect to the nematic director allows the preparation of both cylindrically symmetric and asymmetrically aligned probe distributions whose relaxation dynamics are sensitive to both theta and phi motions yielding two characteristic relaxation times: tau(20) (pure theta-diffusion) and tau(22) (predominantly phi-diffusion). Analysis of the fluorescence intensity decays for excitation polarisation angles of beta=0degrees and beta=54.7degrees allows a determination of the effect of local field and differential reflection losses without the measurement of sample refractive indices. A striking feature of oxazine 4 dynamics in the approach to the nematic-isotropic phase transition temperature (T-NI) is that whilst theta diffusion shows a characteristic Arrhenius temperature dependence, the rate of diffusion in the phi coordinate is reduced as the system becomes less ordered. In the isotropic phase over a 50degreesC temperature range above T-NI the fluorescence anisotropy is characterised by two correlation times consistent with restricted rotational diffusion (intra-domain relaxation tau(f)) within a slowly relaxing (pseudo-domain) structure (tau(s)). The temperature dependence of tau(f) and tau(s) was in good agreement with recent theoretical models for intra- and inter-domain relaxation
