Andrew Beeby

Absolute measurements of photoluminescence quantum yields of solutions using an integrating sphere.

We demonstrate that absolute measurements of the photoluminescence quantum yield of solutions can be made using an integrating sphere and a conventional fluorimeter. With this method the need for measurements against a luminescence standard is overcome. The sphere is mounted inside a commercial fluorimeter, which gives flexibility in excitation and emission wavelength ranges. A number of compounds have been investigated and the results are compared to literature values and data obtained using a comparative method.

Luminescence imaging microscopy and lifetime mapping using kinetically stable lanthanide(III) complexes.

The sensitised luminescence from stable lanthanide complexes (1 and 2) bearing a phenanthridine antenna has been used to generate time-resolved images of silica particles. The millisecond order luminescent lifetime of these complexes is utilised to demonstrate time-gated imaging of the sample from a fluorescent background and to facilitate lifetime mapping over the area of the sample.

PHTHALOCYANINE FLUORESCENCE AT HIGH CONCENTRATION: DIMERS OR REABSORPTION EFFECT?

Abstract— For tetrasulfonated aluminum phthalocyanine (AlPcS4), dimer formation is characterized in the absorption spectrum by a broadening of the Q‐band and the appearance of a new band at the red edge of the spectrum. The high concentrations required to produce dimers, however, often leads to anomalous observations in fluorescence spectroscopy. In the present study, we have examined the photophysical characteristics of two dye systems; AlPcS4 in a 66% ethanol/water mixture and disulfonated aluminum phthalocyanine in methanol. Using absorption spectroscopy, the formation of dimers is shown to be prevalent only in the case of AlPcS4. The fluorescence emission spectra in both cases, however, exhibit similar spectral changes with increasing dye concentration. The measured fluorescence decay profiles for both dyes also show similar trends: They are monoexponential, invariant with emission wavelength and have decay times that increase with dye concentration. These distortions are sometimes incorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence and demonstrate that these data can be readily explained, by taking into consideration the effects of reabsorption of fluorescence.

The synthesis and one- and two-photon optical properties of dipolar, quadrupolar and octupolar donor–acceptor molecules containing dimesitylboryl groups

Two series of related donor-acceptor conjugated dipolar, pseudo-quadrupolar (V-shaped) and octupolar molecular systems based on the p-dimesitylborylphenylethynylaniline core, namely, 4-(4-dimesitylborylphenylethynyl)-N,N-dimethylaniline, 4-[4-(4-dimesitylborylphenylethynyl)phenylethynyl]-N,N-dimethylaniline, 3,6-bis(4-dimesitylborylphenylethynyl)-N-n-butylcarbazole and tris[4-(4-dimesitylborylphenylethynyl)phenyl]amine, and on the E-p-dimesitylborylethenylaniline motif, namely, E-4-dimesitylborylethenyl-N,N-di(4-tolyl)aniline, 3,6-bis(E-dimesitylborylethenyl)-N-n-butylcarbazole and tris(E-4-dimesitylborylethenylphenyl)amine have been synthesised by palladium-catalyzed cross-coupling and hydroboration routes, respectively. Their absorption and emission maxima, fluorescence lifetimes and quantum yields have been obtained and their two-photon absorption (TPA) spectra and TPA cross-sections have been examined. Of these systems, the octupolar compound tris(E-4-dimesitylborylethenylphenyl)amine has been shown to exhibit the largest TPA cross-section among the two series of approximately 1000 GM at 740 nm. Its TPA performance is comparable to those of other triphenylamine-based octupoles of similar size. The combination of such large TPA cross-sections and high emission quantum yields, up to 0.94, make these systems attractive for applications involving two-photon excited fluorescence (TPEF).

Efficient Sensitization of Europium, Ytterbium, and Neodymium Functionalized Tris-Dipicolinate Lanthanide Complexes through Tunable Charge-Transfer Excited States

A series of push-pull donor-pi-conjugated dipicolinic acid ligands and related tris-dipicolinate europium and lutetium complexes have been prepared. The ligands present broad absorption and emission transitions in the visible spectral range unambiguously assigned to charge-transfer transitions (CT) by means of time-dependent density functional theory calculations. The photophysical properties (absorption, emission, luminescence quantum yield, and lifetime) of the corresponding europium complexes were thoroughly investigated. Solvatochromism and temperature effects clearly confirm that Eu(III) sensitization directly occurs from the ligand CT state. In addition, modulation of the energy of the CT donating state by changing the nature of the donor fragment allows the optimal energy of the antennae for europium sensitization to be determined, and this optimal energy was found to be close to the (5)D 1 accepting state. Finally, this CT sensitization process has been successfully extended to near-infrared emitters (neodymium and ytterbium).

Luminescence from neodymium(III) in solution

Abstract The luminescence lifetime of neodymium(III) in aqueous and organic solutions has been measured for the first time, and the effects of solvent deuteration on the excited state decay kinetics investigated. We have shown that the emissive 4 F 3 2 state is very short lived in water, τ = 29 ± 3 ns, and the lifetimeincreases significantly upon changing to D2O, τ = 152 ± 7 ns. Complexing to polydentate ligands such as EDTA increases the lifetime due to the reduced solvation of the ion by water. In organic solvents the lifetime of the excited state of the ion is affected by both the presence of CH and OH oscillators; the latter are much more efficient at deactivating the excited state.

3‐Hydroxypyridin‐2‐one Complexes of Near‐Infrared (NIR) Emitting Lanthanides: Sensitization of Holmium(III) and Praseodymium(III) in Aqueous Solution

There is a growing interest in Near Infra-Red (NIR) emission originating from organic complexes of LnIII cations.[1,2] As a major impetus, biological tissues are considerably more transparent at these low energy wavelengths when compared to visible radiation, which facilitates deeper penetration of incident and emitted light.[3] Furthermore, the long luminescence lifetimes of LnIII complexes (eg. YbIII, τrad ~ 1 ms) when compared to typical organic molecules can be utilized to vastly improve signal to noise ratios by employing time-gating techniques. While the improved quantum yield of YbIII complexes when compared to other NIR emitters favours their use for bioimaging applications, there has also been significant interest[4,5,6] in the sensitized emission from other 4f metals such as Ln = Nd, Ho, Pr and Er which have well recognised applications as solid state laser materials[7] (eg. Nd ~ 1.06 μm, Ho ~ 2.09 μm), and in telecommunications (eg. Er ~ 1.54 μm) where they can be used for amplification of optical signals.[8]

The preparation and photophysical measurements of perdeutero zinc phthalocyanine

Abstract The fully deuterated photosensitizer, zinc phthalocyanine- d 16 , was synthesized and its excited singlet and triplet state photophysics determined. Surprisingly, no differences in the excited state kinetics or quantum yields were observed compared with the undeuterated material. Furthermore, deuteration of the axial pyridine ligand of the metallophthalocyanine produced no changes in its photophysical behaviour. These results are compared with recent work (A. Beeby, A.W. Parker, M.S.C. Simpson and D. Phillips, J. Photochem. Photobiol. B: Biol., 16 (1992) 73–81) in which the photophysical properties of aluminium phthalocyanines were altered in deuterated solvents, and the effects of deuteration on the non-radiative relaxation processes of phthalocyanines were discussed. Implications for the use of such compounds in photodynamic therapy are also mentioned.

Time-resolved near-IR luminescence from ytterbium and neodymium complexes of the Lehn cryptand

Abstract The Lehn cryptand has been widely applied to the study and application of luminescent lanthanide ions. We have demonstrated that the ytterbium and neodymium complexes are also luminescent. The luminescence lifetimes of the ytterbium complex fit well to established models for determining the number of inner sphere water molecules. By contrast, the neodymium complex exhibits unusually long lifetimes in aqueous media when compared to those observed with aminocarboxylate ligands. This behaviour may be ascribed to the relatively small number of proximate C–H oscillators in the cryptate.

Blending Gelators to Tune Gel Structure and Probe Anion-Induced Disassembly

Blending different low molecular weight gelators (LMWGs) provides a convenient route to tune the properties of a gel and incorporate functionalities such as fluorescence. Blending a series of gelators having a common bis-urea motif, and functionalised with different amino acid-derived end-groups and differing length alkylene spacers is reported. Fluorescent gelators incorporating 1-and 2-pyrenyl moieties provide a probe of the mixed systems alongside structural and morphological data from powder diffraction and electron microscopy. Characterisation of the individual gelators reveals that although the expected α-urea tape motif is preserved, there is considerable variation in the gelation properties, molecular packing, fibre morphology and rheological behaviour. Mixing of the gelators revealed examples in which: 1) the gels formed separate, orthogonal networks maintaining their own packing and morphology, 2) the gels blended together into a single network, either adopting the packing and morphology of one gelator, or 3) a new structure not seen for either of the gelators individually was created. The strong binding of the urea functionalities to anions was exploited as a means of breaking down the gel structure, and the use of fluorescent gel blends provides new insights into anion-mediated gel dissolution.