The spectroscopy and dynamics of the low-lying triplet state of the proton-transfer tautomer in salicylaldehydes have been studied via internal heavy-atom effects coupled with a sensitive near-IR detecting system. For 3,5-diiodo-salicylaldehyde a weak proton-transfer keto-tautomer phosphorescence was resolved with a maximum at 710 nm (tau(P) - 1.8 mus, Phi(obs) similar to 5.23 x 10(-4)) in a 77 K methylcyclohexane glass. The results, in combination with the time-resolved thermal lensing experiment, further deduced the triplet-state population yield and radiative decay rate to be 0.20 (298 K) and 3.12 x 10(2) s(-1), respectively. Consequently, the energetics and dynamics of the triplet states during a proton transfer cycle are discussed in detail. (C) 2003 Elsevier Science B.V. All rights reserved.