Design and synthesis of organic-inorganic hybrid materials have attracted widespread interest in terms of fundamental and applied researches. Many different kinds of chromophores such as pyrene, porphyrin, phthalocyanine and fullerene have been used to assemble on the surface of gold nanoclusters by self-assembled monolayers (SAMs). In most cases, the excited states of chromophores are significantly quenched by surface-dipole energy transfer (SET) to the gold surface. Actually, the fluorescence emission decreases by more than 90% and generation of triplet states through intersystem crossing is basically negligible. The rate of SET is proportional to the inverse fourth power of the distance between the chromophore and gold surface in point-to-surface approximation. Accordingly, SET is highly related to Förster theory, where the rate constant of energy transfer is proportional to the spectral overlap between the donor (D) emission and acceptor (A) absorption and to the inverse sixth power of the distance between the D and A in point-to-point approximation. In contrast to the above-mentioned gold nanoclusters modified by chromophores, the number of reported examples on chromophore-modified gold nanorods is extremely limited. Little attention has been accordingly drawn toward the comparison of spectroscopic and photophysical properties of chromophore-modified gold nanomaterials with different sizes and shapes.

We have recently reported the synthesis and photophysical properties of 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene-alkanethiolate MPCs [denoted as TP-Cn-X-MPC] with different chain lengths and particle sizes.[1] The occurrence of effcient singlet fission was successfully observed. However, supramolecular intercalation of TP-modified MPCs with guest molecules has yet to be examined. Based on the above points, our focus in this study is to newly synthesize TP-alkanethiolate monolayer-protected gold nanorods [denoted as TP-Cn-MPRs] and compare the spectroscopic and structural properties with the TP-Cn-MPCs. [2] The other point in this prsentation is control and switching of excited-state dynamics in self-assembled monolayes composed of plural chromophores on gold nanoclusters. The details on the structural and photophysical properties of these nanomaterials will be discussed here.

References

[1] Hasobe, T. et al, Angew. Chem. Int. Ed. 2016, 55, 5230-5234.

[2] Hasobe, T. et al, J. Phys. Chem. C 2017, 121, 9043-9052.