(Invited) Distance Dependent Electron Transfer Kinetics in Water Soluble Axially Connected Silicon Phthalocyanine-Fullerene Conjugates

The effect of donor-acceptor distance in controlling the rate of electron transfer in axially linked silicon phthalocyanine – C 60 dyads has been investigated. Herein we will presented the synthesis and photophysical properties of two water soluble C 60 -SiPc-C 60 dyads, 1 and 2 , varying in their donor-acceptor distance.In previous investigation for C 60 -SiPc-C 60 dyads where the SiPc and C 60 are separated by a phenyl spacer, faster electron transfer was observed with k cs equal to 2.7 x 10 9 s -1 in benzonitrile. However, in the case of C 60- SiPc-C 60 , where SiPc and C 60 are separated by a biphenyl spacer, a slower electron transfer rate constant, k cs equal to 9.1 x10 8 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 3 SiPc* 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 .+ -C 60 .- charge separated states (1.57 eV) to populate the low-lying 3 SiPc* (1.26 eV) prior returning to the ground state.[1] Here we will present our recent results using water soluble SiPc-C 60 1-2 systems where the SiPc is substituted with pyridine units.[3] Acknowledgments This work was supported by the Ministerio de Ciencia e Innovación of Spain and FEDER funds (Grants PID2020-117855RB-I00 to ASS) and National Science Foundation (Grant No. 1401188 and 2000988 to FD). References 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. V. Sobrino, L. Martín-Gomis, S. Seetharaman, P. A. Karr, D’Souza, and Á. Sastre-Santos, under preparation. Figure 1