DIMERIZATION PROCESSES OF TRIARYL PYRYLIUM SALTS

The present paper deals with dialkylamino 2,4,6-triaryl pyrylium tetra fluoroborates studied in solution at room temperature. It is intended to clarify the dimerisation process described previously. The photophy sical properties of the didodecylamino derivative, the synthesis of wh ich is reported for the first time, are practically identical to those of the methyldodecylamino analogue, but its solubility in non-polar s olvents is higher by two orders of magnitude allowing a better investi gation of the dimers. The absorption spectra of both compounds, record ed as a function of concentration in solvents of low dielectric consta nt, exhibit isosbestic points. Different equilibria, involving the cat ionic chromophore and its counterion, are discussed. Two-dimensional H -1-NMR experiments performed by off-resonance ROESY (Rotating frame nu clear Overhauser Effect Spectroscopy) confirm dimerisation. Electrical conductivity measurements show that in the monomer-dimer equilibrium related to the isosbestic point, the ''monomer'' corresponds to an ion -pair and the ''dimer'' is composed of two ion-pairs.