Effect of Mutual Position of Electron Donor and Acceptor on Photoinduced Electron Transfer in Supramolecular Chlorophyll–Fullerene Dyads

Abstract

In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.

Coordination chemistry on carbon surfaces

“…42). The computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C 60 [315].…”

Theoretical estimation of the rate of photoinduced charge transfer reactions in triphenylamine C60 donor–acceptor conjugate

“…TPA is able to confine cationic charge and hamper aggregation between molecules, which induces self-quenching and reduces the electron injection efficiency. [31,33] On the other hand, C60 is an excellent electron donor [35][36][37][38] that can react with a variety of chemical agents. [39][40][41][42][43][44] Recently, based on electrochemical and photophysical studies, Echegoyen et al [45] determined kct for the TPA-C60 and TPA-Sc3N@Ih-C80 donor-acceptor conjugates and showed that (i) ultrafast charge separation (CS) reactions occur at the molecular interface, thus giving evidence of CT activity; (ii) TPA-Sc3N@Ih-C80 generates longer-lived photoinduced charge transfer states (CTSs) than does TPA-C60; (iii) increasing the distance of the donor-acceptor interface produces longer-lived CTSs; (iv) nonpolar solvents bring about lack of CT activity; on the contrary, more polar solvents can slow down the charge recombination (CR) reaction; (v) a smaller value of kct for the CR reaction with Sc3N@Ih-C80 in comparison with C60 was found, which was attributed to a smaller value of the driving force.…”

Harnessing the Synergistic and Complementary Properties of Fullerene and Transition-Metal Compounds for Nanomaterial Applications

“…The systems formed using this two-point binding arrangement displayed slightly higher association constants of the order of 10 4 M -1 . [248][249][250][251][252][253] It was possible to generate charge-separated species upon photoexcitation however the average lifetimes were slightly lower than the non-pyridyl systems in the hundreds of nanoseconds range. [249,253] …”