Fluorescence spectroscopy is a technique that is ideally suited for the undergraduate laboratory curriculum.

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N-(aminoalkyl)-4-chloronaphthalene-1,8-dicarboximides 1, N-(aminoalkyl)-4-acetamidonaphthalene-1,8-dicarboximides 3 and N,N'-bis(aminoalkyl)-perylene-3,4:9,10-tetracarboxydiimides 4 show good fluorescent off ± on switching in aqueous alcoholic solution with protons as required for fluorescent PET sensor design. The excitation wavelengths lie in the ultraviolet (l max 345 and 351 nm) for 1 and 3 and in the blue-green (l max 528, 492 and 461 nm) for 4; the emission wavelengths lie in the violet (l max 408 nm) for 1, in the blue (l max 474 nm) for 3 and in the yellow-orange (l max 543 and 583 nm) for 4. Compound 4 b shows substantial fluorescence enhancement with protons when immobilized in a poly(vinylchloride) matrix, provided that 2-nitrophenyloctyl ether plasticizer and potassium tetrakis(4-chlorophenyl)borate additive are present to prevent dye crystallization and to facilitate proton diffusion into the membrane, respectively.