Multispectral imaging is a powerful technique for the non-invasive analysis of medieval manuscripts, providing a rapid assesment of a manuscript prior to analysis by other methods such as Raman or full-spectrum reflectance spectroscopy. In this paper I demonstrate how simple MSI is used to differentitate blue pigments on the page, and demonstrate that arists of the 15th centrury used pigments in a vert speicifc and deliberate way.
Ultra-fast frame rate CMOS cameras, combined with a photon counting image intensifier, can be used for microsecond resolution wide-field time-correlated single photon counting (TCSPC) microscopy. A sequence of frames is recorded after an excitation pulse, and the number and location of photons in each frame is determined. This process is repeated until enough photons are recorded for a photon arrival time histogram in the pixels of the image. This approach combines low, nanowatt excitation power with single-photon detection sensitivity and arrival timing in many pixels simultaneously, short acquisition times in the order of seconds and allows lifetime mapping with a time resolution of ~1 microsecond. Moreover, we also show that the phosphor decay can be exploited to time the photon arrival well below the exposure time of the camera. This approach yields better time resolution and larger images than direct imaging of photon events. We show that both methods are ideal for lifetime imaging of transition metal compounds in living cells within a few seconds.
A study of a group of compounds based on the 1,4-bis(phenylethynyl)benzene (1) architecture was undertaken to
improve our understanding of their photophysics and the factors which control their geometry and hence the π-
conjugation pathway in the ground and excited state of these compounds. 1 exists as a range of molecular rotamers in
the ground state, resulting from the low barrier to rotation around their C(sp)-C(sp2) bonds. These compounds are
highly conjugated systems with good electron conducting properties, due to delocalisation of the HOMO and LUMO
over the molecule. In the electronic excited state they are capable changing their molecular conformation and will adopt
a planar, or near planar, low energy conformation prior to fluorescence emission in solution. In a glassy matrix at 77 K
with sterically hindering substituents on the benzene rings of 1, emission form high and low energy conformations are
observed. 1 is highly emissive owing to the high oscillator strength of the S1→S0 transition. All the compounds studied
maintained their C≡C character in the excited singlet and triplet states. The substitution of the central benzene ring in 1
with a thiophene moiety increases the singlet oxygen generation quantum yield, which is consistent with greater
intersystem crossing to the triplet excited state.
Molecular two-photon absorption (TPA) has attracted a lot of interest over recent years due to the many applications it offers both in biological imaging and in material science, constantly needing new optimized molecules with large TPA cross-sections. Various structures and functional groups have been studied; however, the use of electron-withdrawing boron groups has not been fully examined yet. As such compounds are known to lead to interesting photoluminescence and nonlinear optical (NLO) properties, we have investigated the TPA properties of a novel series of A-π-A quadrupoles, based on dimesitylborons as acceptor end-groups. Our experimental study reveals that intramolecular charge transfer is a crucial point in these TPA fluorophores, and can be modulated via changing the planarity of the molecule. We have obtained such planar molecules using vinylene spacers, which can release the steric hindrance close to the dimesitylboron end-group. The series of NLO-phores described here is promising for optical power limiting, with excellent TPA/transparency trade-off, and the work has highlighted that perfluorophenylene could be a key component for the future of TPA.
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