Unusually large Stokes shift for a near-infrared emitting DNA-stabilized silver nanocluster

Abstract

In this paper we present a new near-IR emitting silver nanocluster (NIR-DNA-AgNC) with an unusually large Stokes shift between absorption and emission maximum (211 nm or 5600 cm). We studied the effect of viscosity and temperature on the steady state and time-resolved emission. The time-resolved results on NIR-DNA-AgNC show that the relaxation dynamics slow down significantly with increasing viscosity of the solvent. In high viscosity solution, the spectral relaxation stretches well into the nanosecond scale. As a result of this slow spectral relaxation in high viscosity solutions, a multi-exponential fluorescence decay time behavior is observed, in contrast to the more mono-exponential decay in low viscosity solution.

Unusually large fluorescence quantum yield for a near-infrared emitting DNA-stabilized silver nanocluster

“…In order to shed light on the relationship between DNA sequence and the optical properties of DNA-AgNCs, we have in recent years focused on studying the photophysical properties of HPLC-purified DNA-AgNCs; this step of purification ensures that a single type of emissive DNA-AgNC species is studied. [6][7][8][9] Recently, crystal structure data of DNA-AgNCs has appeared in the literature, which will become a key part in understanding the relationship between DNA sequence and optical properties of the DNA-AgNCs. 10,11 In this paper, we have studied the photophysical properties of a NIR-emitting DNA-AgNC, stabilized by the sequence 5 0 -CCCGGAGAAG-3 0 .…”

“…S4, ESI †), indicating that two, if not three, DNA strands stabilize this AgNC. The latter argument is based on comparing the hydrodynamic volume of another NIR-emitting DNA-AgNC composed of 16 silver atoms stabilized by two 10-base oligonucleotides 8 which has a hydrodynamic volume of 10.5 nm 3 .…”

Crystal structure of a NIR‐Emitting DNA‐Stabilized Ag16 Nanocluster

“…The fluorescence spectra of five different crystals can be found in Figure S1 in the Supporting Information. We tentatively attribute this blue‐shift to a reduced spectral relaxation of the DNA–Ag 16 NC due to the restricted mobility in the crystal versus the solution case. Interestingly, the crystal emission maximum is identical to that of the DNA–Ag 16 NCs in a high viscous medium (90 % glycerol, 10 % 10 m m ammonium acetate solution), where reduced spectral relaxation has been observed .…”

“…The decay curve (Supporting Information, Figure S2 A) was tail‐fitted with a bi‐exponential model and an average decay time of 2.26 ns was found. The lifetime of the DNA‐Ag 16 NCs in the crystal is approximately 1.0 ns shorter than the decay time of the DNA–Ag 16 NCs in solution . The origin of this shortening is not clear at this point but is most likely due to the close proximity of the DNA–Ag 16 NCs to each other.…”

“…In order to verify that the crystal structure of the DNA–Ag 16 NC did not dramatically differ from the solution structure, fluorescence measurements were performed. In solution, at 298 K, the DNA–Ag 16 NC has an unusually large Stokes shift ( =525 nm, =736 nm) . Using a wide‐field microscope, we performed bright‐field (Figure A) and fluorescence measurements (Figure B) on the as‐grown crystals in the well plate.…”