TY - JOUR AU - Villamaina, Diego AU - Kelson, Melissa AU - Bhosale, Sheshanath AU - Vauthey, Eric TI - Excitation wavelength dependence of the charge separation pathways in tetraphorphyrin-naphthalene diimide pentads PY - 2014 JF - Physical Chemistry Chemical Physics JA - Phys. Chem. Chem. Phys. SN - 1463-9076 VL - 16 IS - 11 SP - 5188 EP - 5200 L1 - http://pubs.rsc.org/en/content/articlepdf/2014/cp/c3cp54871f L2 - http://pubs.rsc.org/en/content/articlehtml/2014/cp/c3cp54871f L3 - http://pubs.rsc.org/en/Content/ArticleLanding/2014/CP/c3cp54871f L4 - http://www.unige.ch/sciences/chifi/publis/pics/double/ref01393.png M3 - 10.1039/c3cp54871f UR - http://dx.doi.org/10.1039/c3cp54871f N2 - The excited-state dynamics of two multichromophoric arrays composed of a naphthalene diimide centre and four zinc or free-base porphyrins substituted on the naphthalene core via aniline bridges has been investigated using a combination of stationary and ultrafast spectroscopies. These pentads act as efficient antennae as they absorb over the whole visible region, with a band around 700 nm, associated with a transition to the S1 state delocalised over the whole arrays, and bands at higher energy due to transitions centred on the porphyrins. In non-polar solvents, population of these porphyrin states is followed by sub-picosecond internal conversion to the S1 state. The existence of a charge-separated state located above the S1 state could enhance this process. The decay of the S1 state is dominated by non-radiative deactivation on the 100 ps timescale, most probably favoured by the small S1-S0 energy gap and the very high density of vibrational states of these very large chromophores. In polar solvents, the charge-separated state lies just below the S1 state. It can be populated within a few picoseconds by a thermally-activated hole transfer from the S1 state as well as via sub-picosecond non-equilibrium electron transfer from vibrationally hot porphyrin excited states. Because of the small energy gap between the charge-separated state and the ground state, charge recombination is almost barrierless and occurs within a few picoseconds. Despite their very different driving forces, charge separation and recombination occur on similar timescales. This is explained by the electronic coupling that differs considerably for both processes. ID - 1393 ER -