Environmental Effects on Phosphorescence. IV. Triplet Decay of Halonaphthalenes in Compressed PMMA

The effects of high pressure (0–32 kbar) on the phosphorescence lifetime ${\tau }_p$ of seven monohalogen‐substituted naphthalenes, dispersed in polymethylmethacrylate (PMMA), have been measured at room temperature. It is observed that the pressure‐induced shortening of the lifetimes becomes less significant in those halonaphthalenes which possess the heavier atoms, i.e., the greater the intramolecular heavy‐atom effect the less influential are environmental perturbations. “Activation volumes,” ranging in magnitude between ${\text{−\hspace{0.17em}0.25\hspace{0.17em}<\hspace{0.17em}ΔV}}^{‡}{\text{\hspace{0.17em}<\hspace{0.17em}0.0 Å}}^3/\mathrm{molecule}$ , were computed from linear $\ln {\tau }_p‐\mathrm{vs}\mathrm{‐P}$ plots. Qualitative arguments are given to support the observed magnitudes and trends in the pressure‐induced volume effects on triplet decay.