Spectroscopic properties of aromatic dicarboximides. Part1.—N—H and N-methyl-substituted naphthalimides

摘要: The photophysical properties of the N—H and N-methyl derivatives 1,2-, 2,3- 1,8-naphthalimides have been studied. shift fluorescence emission position as a function solvent polarity indicates only weak variation dipole moment for excited state compared with corresponding value in ground (5.7 D 2b, 2.8 3b <2 4b, 1 ≈ 3.335 64 × 10–30 C m, 4b are N-methyl-1,2- naphthalimide, N-methyl-2,3-napthalimide N-methyl-1,8-naphthalimide). However, important modifications observed which depend on relative dicarboximide moiety naphthalene ring: intersystem crossing rate constant increases dramatically by three orders magnitude that 2b; simultaneously, quantum yield decreases from 0.77 to 0.03, although constant, kf, increases. This difference is found arise energy gap between lowest1(π, π*) singlet upper 3(n,π*) triplet state, order 9 kcal mol–1 2b less than 2 acetonitrile solution. Protic solvents increase n,π* π,π* states thus decreasing mixing two levels; consequence, lifetime increased, i.e. <60 ps hexane 2.1 ns trifluoroethanol. A triplet–triplet annihilation process occurs leads monomer delayed former, mainly excimer latter.