New dyad and triad systems based on a zinc porphyrin (ZnP), a naphthalenediimide (NDI), and a ferrocene (Fc) as molecular components, linked by 1,2,3-triazole bridges, ZnP-NDI (3) and Fc-ZnP-NDI (4), have been synthesized. Their photophysical behavior has been investigated by both visible excitation of the ZnP chromophore and UV excitation of the NDI unit. Dyad 3 exhibits relatively inefficient quenching of the ZnP singlet excited state, slow charge separation and fast charge recombination processes. Excitation of the NDI chromophore, on the other hand, leads to charge separation by both singlet and triplet quenching pathways, with the singlet charge-separated (CS) state recombining in a sub-ns time scale, and the triplet CS state decaying in ca. 90 ns. In the triad system 4, primary formation of Fc-ZnP+-NDI− charge separated state is followed by a secondary hole shift process from ZnP to Fc. The product of the stepwise charge-separation, Fc+-ZnP-NDI−, undergoes recombination to the ground state, as expected for a long-range process, in a much longer time scale, 1.9 s. The charge separated states are always formed more efficiently upon NDI excitation than upon ZnP excitation. DFT calculations on a bridge-acceptor fragment show that the bridge is expected to mediate a fast donor-to-bridge-to-acceptor electron cascade following excitation of the acceptor. More generally, triazole bridges may behave asymmetrically with respect to photoinduced electron transfer in dyads, kinetically favoring hole-transfer pathways triggered by excitation of the acceptor over electron-transfer pathways promoted by excitation of the donor.
Long Range Charge Separation in a Ferrocene-(Zinc Porphyrin)-Naphthanenediimide Triad with 1,2,3-Triazole Linkers
NATALI, Mirco;RAVAGLIA, Marcella;SCANDOLA, Franco;
2013
Abstract
New dyad and triad systems based on a zinc porphyrin (ZnP), a naphthalenediimide (NDI), and a ferrocene (Fc) as molecular components, linked by 1,2,3-triazole bridges, ZnP-NDI (3) and Fc-ZnP-NDI (4), have been synthesized. Their photophysical behavior has been investigated by both visible excitation of the ZnP chromophore and UV excitation of the NDI unit. Dyad 3 exhibits relatively inefficient quenching of the ZnP singlet excited state, slow charge separation and fast charge recombination processes. Excitation of the NDI chromophore, on the other hand, leads to charge separation by both singlet and triplet quenching pathways, with the singlet charge-separated (CS) state recombining in a sub-ns time scale, and the triplet CS state decaying in ca. 90 ns. In the triad system 4, primary formation of Fc-ZnP+-NDI− charge separated state is followed by a secondary hole shift process from ZnP to Fc. The product of the stepwise charge-separation, Fc+-ZnP-NDI−, undergoes recombination to the ground state, as expected for a long-range process, in a much longer time scale, 1.9 s. The charge separated states are always formed more efficiently upon NDI excitation than upon ZnP excitation. DFT calculations on a bridge-acceptor fragment show that the bridge is expected to mediate a fast donor-to-bridge-to-acceptor electron cascade following excitation of the acceptor. More generally, triazole bridges may behave asymmetrically with respect to photoinduced electron transfer in dyads, kinetically favoring hole-transfer pathways triggered by excitation of the acceptor over electron-transfer pathways promoted by excitation of the donor.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
