SOLVATOCHROMIC EFFECTS ON THE ELECTRON-EXCHANGE CHEMILUMINESCENCE (CIEEL) OF SPIROADAMANTYL-SUBSTITUTED DIOXETANES AND THE FLUORESCENCE OF RELEVANT OXYANIONS

A comparative spectral study on the intramolecular chemically initiale d electron exchange luminescence (CIEEL) of five spiroadamantyl-substi tuted dioxetanes by various enzymatic and chemical triggers (alkaline phosphatase, HO-, and F-) in protic (H2O, D2O, and MeOH) and aprotic ( MeCN and DMSO) solvents and the fluorescence of the authentic methyl m -oxybenzoate anion in the same media is reported. The present study re veals that the CIEEL spectral maxima are independent of the reaction m edium and the means of triggering, whereas the fluorescence spectrum o f the authentic CIEEL emitter depends on the solvent. In the aprotic s olvents the CIEEL and the fluorescence spectra coincide, while in the protic media the fluorescence maxima of the authentic methyl m-oxybenz oate ion are blue-shifted by ca. 50 nm relative to those of the CIEEL emission. Neither exciplex formation nor specific environmental influe nce of the enzyme on the chemiexcited oxybenzoate accounts for the spe ctral shift between the CIEEL and the fluorescence emissions. The subs titution pattern of the fluorophore is decisive for the observed solve nt effects. For the odd-substituted methyl oxybenzoate, in which the o xy and the ester functionalities are cross-conjugated, a blue shift ap plies in the protic media, but not for the even-patterned methyl oxyna phthoate, with the oxy and ester groups extendedly conjugated. These d ivergent spectral observations are rationalized in terms of hydrogen-b onding effects, which are qualitatively substantiated by the semiempir ical AM1 calculations.