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

Abstract

Novel probes represented 4-substituted 1,8-naphtalic anhydride and 1,8-naphthalimide as a chromophore and sterically hindered amine in the form of parent amine as well as stable nitroxyl radical form were synthesized. Laser flash photolysis was used to examine the triplet route of deactivation. The formation of the triplet state occurred at 355 nm laser excitation exhibiting the absorption in the range 360–700 nm. Triplet states of 1,8-naphthalic anhydride chromophore were quenched by oxygen with rate constant about 2 × 10 9 dm 3 mol −1 cm −1 for unsubstituted and 4-bromo substituted derivatives. The 4-dimethylamino substitution of 1,8-naphthalic anhydride exhibited the triplet state, which was not quenched by oxygen or 1-oxo-2,2,6,6-tetramethylpiperidine (TEMPO). The same effect of 4-dimethylamino substitution was observed on the triplet state of N-(2,2,6,6-tetramethyl-4-piperidinyl)-1,8-naphthalimide. 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.