¹³C isotope shifts of anthracene and naphthalene isomers in triplet state optical spectra

Abstract

Position-specific ¹³C isotope shifts in the T ₁←S ₀ photoexcitation spectra of anthracene and naphthalene crystals containing ¹³C substituted molecules in natural abundance and of material enriched with various synthesized ¹³C isomers are compared. From the spectra of matrix isolated A-h₁₀ in A-d₁₀ and N-h₈ in N-d₈ the individual isotope shifts U ₀ of all the ¹³C monosubstituted isomers are determined (with values U ₀ between 0·7 and 3·5 cm^-1). An additivity rule is established for the U ₀ of the twofold substituted ¹³C ¹³C isomers similar to that found for multiple deuteration. Applying these results also the ¹³C substructure of the excitonic Davydov components in anthracene and naphthalene crystals is understood quantitatively. A correlation between the specific ¹³C isotope shifts and the triplet state spin density distribution is discussed.