The temperature dependence
of the fluorescence and phosphorescence from tyrosine and tryptophan in
poly(vinyl alcohol) films has been studied over the temperature range 90-295 K.
A kinetic scheme is proposed which allows the calculation of activation energies
for excited singlet and triplet state deactivation processes. A single
temperature-dependent radiationless process from the singlet state is observed
for tyrosine and tryptophan, with activation energies of 5.2�0.4 and 7.1�0.6 kJ
mol-1 respectively. However,
two distinct temperature transitions have been detected for triplet-state
relaxation at 180 and 255 K. The role of polymer phase transitions in
determining excited state relaxation pathways of embedded luminescent probes is
discussed.