Spectral properties of probes based on pyrene and piperazine: the singlet and triplet route of deactivation

Nanosecond laser flash photolysis was also used to examine the triplet excited state route of deactivation of these novel probes. The formation of this excited state which exhibits a T-T absorption band in the range 360-550 nm, occurred at 355 nm laser excitation in these probes as well as for parent pyrene. Triplet states of pyrene chromophore of all probes were efficiently quenched by oxygen with rate constant about 2 × 109 dm3 mol−1 s−1. Intermolecular quenching of triplet states of the all probes by N-oxyl radical (1-oxo-2,2,6,6-tetramethylpiperidine, TEMPO) was rather low. The rate constant was evaluated to about 5 × 107 dm3 mol−1 s−1. The intramolecular triplet quenching expressed as the ratio of the rate constants of triplet decay of the oxidized probe PyMePAO to PyMePAH was 5 in methanol and 7.7 in cyclohexane.