The effect of donor-acceptor distance in controlling the rate of electron transfer in axially linked silicon phthalocyanine – C₆₀ dyads has been investigated. Herein we will presented the synthesis and photophysical properties of two C₆₀-SiPc-C₆₀ dyads, 1 and 2, varying in their donor-acceptor distance. In the case of C₆₀-SiPc-C₆₀ 1 where the SiPc and C₆₀ are separated by a phenyl spacer, faster electron transfer was observed with k_cs equal to 2.7 x 10⁹ s^-1 in benzonitrile. However, in the case of C_60-SiPc-C₆₀ 2, where SiPc and C₆₀ are separated by a biphenyl spacer, a slower electron transfer rate constant, k_cs equal to 9.1 x10⁸ s^-1 was recorded. The addition of an extra phenyl spacer in 2 increased the donor-acceptor distance by ~ 4.3 Å, and consequently, slowed down the electron transfer rate constant by a factor of ~3.7. The charge separated state lasted over 3 ns, monitoring time window of our femtosecond transient spectrometer. Complimentary nanosecond transient absorption studies revealed formation of ³SiPc* as the end product and suggested that the final lifetime of charge separated state to be in the 3-20 ns range. Energy level diagram established to comprehend these mechanistic details indicated that the comparatively high-energy SiPc^.+-C₆₀^.- charge separated states (1.57 eV) to populate the low-lying ³SiPc* (1.26 eV) prior returning to the ground state.[1]

Here we will present our recent results using SiPc-C₆₀ systems where the SiPc acts as a acceptor and the C₆₀ as donor.[2]

Acknowledgments

This work was supported by the Ministerio de Ciencia e Innovación of Spain and FEDER funds (Grants PID2020-117855RB-I00 and RED2018- 102471-T to ASS) and National Science Foundation (Grant No. 1401188 and 2000988 to FD).

References

1. L. Martín-Gomis, S. Seetharaman, D. Herrero, P. A. Karr, F. Fernández-Lázaro, F. D’Souza, and Á. Sastre-Santos, Chem Phys. Chem., 2020, 21, 2254-2262.
2. L. Martín-Gomis, S. Seetharaman, P. A. Karr, D’Souza, and Á. Sastre-Santos, under preparation.