Effect of high pressure on photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in liquid 2,2-dimethylbutane (DMB) Original Research Article

The effect of high pressure on the photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in liquid 2,2-dimethylbutane (DMB) was studied by measuring the photoconductivity. The pressure dependence of the cationic polarization energy, estimated from the threshold energies of photoconduction and from values of the electron affinity of the solvent, does not follow Bornʹs formula if the macroscopic dielectric constant is used. This seems to indicate that in the threshold region only molecules where the local density around the solute molecule is higher than average can be ionized. The maximum local density was estimated by taking into account density fluctuations. With this model, agreement with the experimental results could be obtained. The effect of high pressure on the apparent ionization quantum yield and on the shape of photoconductivity spectrum is discussed.