TY - JOUR

T1 - Ultrafast fluorescence dynamics of DNA-based silver clusters

AU - Reveguk, Zakhar

AU - Lysenko, Roman

AU - Ramazanov, Ruslan

AU - Kononov, Alexei

PY - 2018/11/28

Y1 - 2018/11/28

N2 - Atomic-level understanding of the nature of the electronically excited states in ligand-stabilized metal nanoclusters (NCs) is a prerequisite for the design of new NCs with desired properties. In this study, we investigate the emission dynamics of a Ag-DNA complex using the fluorescence up-conversion technique. We show that most of the relaxation from the Franck-Condon state to the emissive state takes place in less than 100 fs, in spite of a relatively large Stokes shift of 4500 cm-1. This relaxation is much faster than typical solvent/DNA relaxation rates. A further small relaxation occurs with time constants ranging from a few to hundreds of picoseconds. We also calculate the Stokes shift for model complexes of a small three-atom Ag3 + cluster with cytosine and guanine. The results of our calculations show that a substantial geometry change of the Ag3 + cluster is observed in the S1 state of both complexes, which results in Stokes shifts comparable with the experimental value. We conclude that the Stokes shift in the Ag-DNA complex arises mostly due to the change in the geometry of the Ag cluster in the excited state rather than to the solvent/DNA reorganization. Also, a different structure of the Ag-DNA complex ("dark cluster"), the excited state of which decays in 200 fs, is observed. The nature of this ultrafast deactivation is unclear, which requires further investigations.

AB - Atomic-level understanding of the nature of the electronically excited states in ligand-stabilized metal nanoclusters (NCs) is a prerequisite for the design of new NCs with desired properties. In this study, we investigate the emission dynamics of a Ag-DNA complex using the fluorescence up-conversion technique. We show that most of the relaxation from the Franck-Condon state to the emissive state takes place in less than 100 fs, in spite of a relatively large Stokes shift of 4500 cm-1. This relaxation is much faster than typical solvent/DNA relaxation rates. A further small relaxation occurs with time constants ranging from a few to hundreds of picoseconds. We also calculate the Stokes shift for model complexes of a small three-atom Ag3 + cluster with cytosine and guanine. The results of our calculations show that a substantial geometry change of the Ag3 + cluster is observed in the S1 state of both complexes, which results in Stokes shifts comparable with the experimental value. We conclude that the Stokes shift in the Ag-DNA complex arises mostly due to the change in the geometry of the Ag cluster in the excited state rather than to the solvent/DNA reorganization. Also, a different structure of the Ag-DNA complex ("dark cluster"), the excited state of which decays in 200 fs, is observed. The nature of this ultrafast deactivation is unclear, which requires further investigations.

KW - EXCITED-STATE RELAXATION

KW - BASIS-SETS

KW - NANOCLUSTERS SYNTHESIS

KW - EXCITATION-SPECTRA

KW - COMPLEXES

KW - RI-MP2

KW - ATOMS

UR - http://www.scopus.com/inward/record.url?scp=85056501914&partnerID=8YFLogxK

UR - http://www.mendeley.com/research/ultrafast-fluorescence-dynamics-dnabased

U2 - 10.1039/c8cp05727c

DO - 10.1039/c8cp05727c

M3 - Article

C2 - 30397702

AN - SCOPUS:85056501914

VL - 20

SP - 28205

EP - 28210

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 44

ER -