DIPOLE DIPOLE INTERACTIONS BETWEEN THE TERMINAL GROUPS OF 1,N-DIARENECARBOXY ALKANES, N=1,2 ... 6

The mutual interaction between the end groups of bichromophoric molecules is studied using absorption and fluorescence techniques (steady-state and time-resolved). With three series of di-1, n-arenecarboxyalkanes (arene = benzene, naphthalene and anthracene; n = 1, 2, 3, 5 and 6) and a series of 1-pyrenecarboxy, n-(N-methyl, N-phenylamino) alkanes (n = 2, 3, 4, 5, 6 and 9), it is found that model compounds such as the methyl, ethyl and hexyl esters of benzene, naphthalene, anthracene and pyrene differ from the bichromophoric compounds in their absorption and emission spectra, molar absorption coefficients and radiative rates constants. These differences decrease with the mean value of the sixth power of the end-to-end distance, being attributed to dipole-dipole interactions between the end groups. The terminal group induces mixing of the lowest excited singlet state with higher energy states and increases the local polarizability of the medium. Two methods for evaluating the unquenched fluorescence lifetimes of bichromophoric compounds are discussed.