Plasmonically Driven Organic Transformation: A Tool to Study the Effect of Nanoparticle Size on Thermoplasmonic Heat Generation

Abstract

A photoexcited plasmonic nanoparticle (NP) can decay both radiatively and nonradiatively. The hot charge carriers and heat (thermoplasmonic heat) generated, via the non-radiative decay pathway, have been used for various chemical and physical transformations. However, the contribution of these two non-radiative decay process in bringing out a particular task is often debated. The main reason for this limitation is the lack of practical techniques available to quantify the thermoplasmonic heat under the conditions of photocatalysis (basically in solution state). In this thesis, we have tried to explore the possibility of using a thermally driven organic transformation as a tool to study the thermoplasmonic heat generated. Here the source of heat was the thermoplasmonic heat generated by photoexcited plasmonic gold NPs (AuNPs). The reaction yield was used the proxy to quantify the thermoplasmonic heat generated: more the yield, more is the thermoplasmonic heat. For this, we have selected the thermal transformation of 3-hydroxy-2-methyl-4-pyrone with methylamine to form the product 3-hydroxy-1,2-dimethyl-pyridin-4-one. We successfully demonstrated that the thermoplasmonic heat from photoexcited AuNPs can drive the organic conversion. This method is more effective to quantify the thermoplasmonic heat as it gives a combined estimate of both localised heating and bulk heating in the system. Using reaction yield as a parameter, we investigated the effect of size of AuNPs on the generation of thermoplasmonic heat. Accordingly, ~10 nm sized AuNP was found to be generating the maximum thermoplasmonic heat under our experimental conditions, which was further independently verified using solar-vapor generation experiments as well.