A. J. Parola

Revisiting Perkin's dye(s): the spectroscopy and photophysics of two new mauveine compounds (B2 and C)

Two new components have been identified in an early sample prepared according to the original recipe of Perkin, and perhaps even by Perkin himself around 1860--a new isomer of Perkins mauveine B (designated as mauveine B2) together with a new mauveine compound (mauveine C)--and these compounds were synthesized again using starting materials chosen to reproduce Perkins original synthesis and isolated by HPLC-DAD, identified by (1)H NMR, MS and their spectroscopic (UV/Vis and emission) and photophysical behaviour investigated.

Photochemistry for Cultural Heritage

Why do certain ancient natural dyes, such as indigo, preserve their colour so well while others, like brazilein, seem to degrade much faster? And how did mauveine change the world of colour? Will modern binding media, as vinyl paints, perform as well as a medieval tempera? Will it be possible to predict their durability? Photochemistry can answer many important questions about materials’ stability, providing new tools for the conservation of treasured artworks.

A fluorescent chemosensor for Zn(II). Exciplex formation in solution and the solid state.

The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9-methylamino)ethyl]-[9]-1,10-phenanthrolinophane (L) bearing a pendant arm containing a coordinating amine and an anthracene group forms stable complexes with Zn(II), Cd(II) and Hg(II) in solution. Stability constants of these complexes were determined in 0.10 mol dm(-3) NMe(4)Cl H(2)O-MeCN (1:1, v/v) solution at 298.1 +/- 0.1 K by means of potentiometric (pH metric) titration. The fluorescence emission properties of these complexes were studied in this solvent. For the Zn(II) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular pi-stacking interaction between phenanthroline and anthracene in the ground state and exciplex emission in the excited state were observed. From the temperature dependence of the photostationary ratio (I(Exc)/I(M)), the activation energy for the exciplex formation (E(a)) and the binding energy of the exciplex (-DeltaH) were determined. The crystal structure of the [ZnLBr](ClO(4)).H(2)O compound was resolved, showing that in the solid state both intra- and inter-molecular pi-stacking interactions are present. Such interactions were also evidenced by UV-vis absorption and emission spectra in the solid state. The absorption spectrum of a thin film of the solid complex is red-shifted compared with the solution spectra, whereas its emission spectrum reveals the unique featureless exciplex band, blue shifted compared with the solution. In conjunction with X-ray data the solid-state data was interpreted as being due to a new exciplex where no pi-stacking (full overlap of the pi-electron cloud of the two chromophores - anthracene and phenanthroline) is observed. L is a fluorescent chemosensor able to signal Zn(II) in presence of Cd(II) and Hg(II), since the last two metal ions do not give rise either to the formation of pi-stacking complexes or to exciplex emission in solution.