We report on the use of time-resolved and polarised evanescent wave-induced fluorescence anisotropy measurements to probe molecular photophysics, motion and energy migration of fluorescent species in close proximity to a silica/film interface. In particular we show that the fluorescence decay and anisotropy of common fluorophores varies as a function of the plane of the fluorophore with respect to the interface, the distance from the interface, and as a function of position (using polarised EW imaging). We have applied time-resolved and polarised EW-induced fluorescence microspectroscopic measurements to dyes, thin polymer nanoparticle films and cells on silica surfaces, probing the variation in the photophysical dynamics within the films.
Efficient conversion of solar energy to electricity in low-cost organic photovoltaic (OPV) devices requires the complex interplay between multiple processes and components over various length and time scales. Optimizing device morphology to ensure efficient exciton diffusion and charge transport as well as ensuring efficient charge photogeneration is necessary to achieve optimum performance in new materials. The conjugated polymer electron donor PFM (poly(9,9-diocetyluorene-co-bis-N,N-(4-methylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine)) and electron acceptor F8BT (poly[(9,9-di-n-octyluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)), comprise the novel triblock copolymer PFM-F8BT-PFM. This copolymer is designed to phase separate on the 20-30 nm scale, a domain size ideal for maximizing exciton collection at the donor-acceptor interface. Using steady-state and ultrafast spectroscopic characterization including high repetition rate transient absorption spectroscopy, the dynamics of charge and energy transfer of the component polymers and the triblock co-polymer have been investigated. The results demonstrate that for the homopolymers solvent dependent exciton transport processes dominate, while in the triblock copolymer solutions transient spectroscopy provides evidence for interfacial charge separation.
Here we report the synthesis and physical characterization of four substituted phenylenevinylene molecules, 1-4, which serve as short chain model oligomers of poly(1,4-phenylenevinylene). Quantum mechanical calculations on alkoxy substituted stilbene derivatives 1 and 2 reveal a direct correlation between the torsional angles and the substituent pattern. HOMO and LUMO energy levels were calculated for all four compounds and showed that the introduction of alkoxy substituents reduce the energy gaps between the ground and first excited singlet states of these molecules. In addition, absorption spectra, fluorescence life-times and quantum yield data of the four compounds are presented.
The benefits of two-photon fluorescence microscopy of biological samples are vast arising from the utilisation of low
energy light. The two-photon absorption cross sections (σ2) of the di-cation free-base and metallated forms of
hematoporphyrin derivative (HpD), hematoporphyrin IX (Hp9) and a boronated protoporphyrin (BOPP) are obtained to
ascertain their effectiveness as fluorophores for use in two-photon microscopy. The open-aperture Z-scan and the two-photon
induced fluorescence (TPIF) techniques, each capable of providing information regarding the nonlinear
absorption, are employed to determine σ2 of the various porphyrins at an excitation wavelength of 800 nm.
A significant disparity in the determined values of σ2 using the two methods is observed. This is largely attributed to the
common requirement of higher concentrations used in the open aperture Z-scan method compared with TPIF techniques.
Values of σ2 obtained from the Z-scan experiments are in the order of 10 GM, whilst those obtained from the TPIF
experiments are in the order of 200 GM. Insertion of either protons or metal ions into the macrocycle does not enhance
the σ2 of the porphyrins. Successful two-photon induced fluorescence imaging of BOPP free-base loaded G6 glioma cells
is achieved, confirming the usefulness of this porphyrin in two-photon microscopy.
Evanescent Wave (EW) fluorescence spectroscopic techniques are exploited to obtain information about the
conformational state of macromolecules within close proximity of a solid/liquid interfacial region. Specifically, timeresolved
evanescent wave-induced fluorescence techniques have been applied to the study of the adsorption of polymers
and biomolecules to silica surfaces. We have extended these EW measurements using polarized excitation and emission
detection to probe molecular motion and conformational change in the microenvironment of the interfacial region. We
report on the observation of complex time-dependent fluorescence anisotropy data and the interpretation of these data in
terms of in- and out-of-plane rotational motion. The macromolecular-interfacial systems investigated by this evanescent
wave approach included polymer film dynamics and adsorbed protein rearrangement upon adsorption.