Synthesis and transient absorption spectra of derivatives of 1,8-naphthalic anhydrides and naphthalimides containing 2,2,6,6-tetramethylpiperidine; triplet route of deactivation

In the series of 4-bromo-N-(2,2,6,6-tetramethyl-4-piperidinyl)-1,8-naphthalimide derivatives, the weak transient triplet absorption was observed for 1-oxo derivative. Probably, the decay of triplet state of 1,8-naphthalimide chromophore is fast due to combination of two effects: paramagnetic effect of free N-oxyl radical and heavy atom effect of bromo substituent.