seminars

The use of photoacids and photobases to control the dynamic self-assembly of gold nanoparticles in aqueous and non-aqueous solutions

Physical and Analytical Chemistry Seminar

Lecturer: Anna Yucknovsky

Date:
15-15 Jan 2019 @ 15:30

Location: Faculty Seminar Room

Abstract

Dynamic self-assembly of nanoparticles for the formation of ordered clusters is taking place out of thermodynamic equilibrium, and thus, sustained by external energy supply. Here we present light energy driven dynamic self-assembly of gold nanoparticles (AuNPs), decorated with pH sensitive ligands, involving either excited state proton or hydroxide transfer phenomena. These processes are mediated by a photoacid or a photobase, which are defined as aromatic molecules that display properties of weak acid or base in their ground electronic state, but exhibit large pKa drop or increase, respectively, in their excited state. We achieve fast (seconds) control over AuNPs self-assembly by combining both photoacid (pyranine) and a photobase (6-methoxyquinoline), having a different wavelength of excitation, and in this way, a significant pKa gap arises simply by changing the wavelength of excitation. An additional approach that we show is based on the employment of a very strong photobase (malachite green carbinol base, MGCB) that releases hydroxide, having a significant pKa gap between its excited and ground states and a fast dissociation rate. To address the recombination time aspect, we synthesized methylated derivative of MGCB with extra positive charge, MGCB+, and tested the effect of enhanced Coulombic force between the released hydroxide anions and MGCB2+ cations.