Ground (S0) and first excited singlet state (S1) potential energy surfaces were calculated for a series of six symmetric carbocyanines as a function of the twisting angle (θ), around a carbon−carbon bond of the polymethine chain. The surfaces were computed using AM1 semiempirical quantum mechanical calculations. Rotations around different bonds were considered in order to determine the relevant rotation for isomerization, that is, the rotation with the lowest activation energy for the isolated molecule (E 0). For that rotation, the computed values of E 0 are in good agreement with values extrapolated from experiments in solutions of n-primary alcohols. The same holds for the computed transition energies between both surfaces for the thermodynamically stable N isomer (θ = 0°) and the P photoisomer (θ = 180°). The effects of chain length and pattern substitution of the indoline moiety on E 0 were also analyzed for both surfaces. The shape of the potential surfaces referred as the Rullière's model holds in all cases for at least one rotational coordinate. The electrical dipole moment with respect to the center of electrical charges was calculated as a function of θ. The calculations show that the dipole moment remains almost constant except in the vicinity of θ = 90°, where a sudden increase with a sharp peak was obtained in both surfaces. This gives a simple explanation for the well-known experimental observation that the activation energy on the excited state surface is independent of solvent polarity, as the angle of the transition state is smaller than 90°. On the other hand, the transition state is at θ = 90° on the ground state, and a polarity influence is predicted. An improvement in the description of the experimental isomerization rate constants in S0 is obtained for the two smallest carbocyanines considered when polarity contributions are included.

Excited state deactivation of a zinc phthalocyanine (ZnPc) by amines was studied in micelles of hexadecyltrimethylammonium chloride. The singlet state deactivation was studied by fluorescence quenching. This technique allows us to determine equilibrium constants for the distribution of the amines between the aqueous and the micellar phases. It could be established that amines associate to the micelles in two different ways: with a greater affinity to a saturable number of sites, that we will term binding sites, and with a lower affinity by a partitioning mechanism. Equilibrium constants could be determined for aliphatic and aromatic amines. A kinetic scheme taking into account the simultaneous quenching of ZnPc fluorescence by the two types of micellized amines could be successfully applied to derive singlet quenching rate constants, under the assumption that micelles behave like closed compartments during the singlet deactivation. Aromatic amines are more efficient than aliphatic ones, and partitioned quenchers are more effective than bound quenchers. Aromatic amines also deactivate the triplet state of ZnPc. By flash photolysis, the absorption of the anion radical of ZnPc was detected. This species originates on singlet and triplet quenching, indicating that both proceed by electron transfer.