The energy gap law relates the nonradiative decay rate to the energy gap separating the ground and excited states. Here we report that the energy gap law can be applied to exciton dynamics in gold cluster molecules. Size-dependent electrochemical and optical properties were investigated for a series of n-hexanethiolate-protected gold clusters ranging from Au25 to Au333. Voltammetric studies reveal that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of these clusters decrease with increasing cluster size. Combined femtosecond and nanosecond time-resolved transient absorption measurements show that the exciton lifetimes decrease with increasing cluster size. Comparison of the size-dependent exciton lifetimes with the HOMO-LUMO gaps shows that they are linearly correlated, demonstrating the energy gap law for excitons in these gold cluster molecules.
Bibliographical noteFunding Information:
D.L. acknowledges support by the Korea CCS R&D Center (KCRC) grant (NRF-2014M1A8A1074219), the NRF grant (NRF-2014R1A2A1A11051032 and 2009-0093823), and the Yonsei University Future-leading Research Initiative of 2014. G.R. acknowledges the support of ACS-PRF #53999-ND5 and Western Michigan University startup. G. R. also acknowledges Dr. Gary Wiederrecht, Argonne National Laboratory, for help with transient absorption measurements. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
© 2017 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry