Aspect Ratio of Gold Nanorods Indirectly Modulates the Performance of Plasmonic-Photochromic Fibers: A Spectroscopic Study.

Plasmonic-photochromic materials have been widely investigated to harness photoresponsive properties of both components, particularly in systems comprising gold nanoparticles (AuNPs) and azobenzenes (Azos). Although AuNPs affect Azo performance, there is no information on how to employ their morphology to systematically modulate kinetics and thermodynamics of the photochromes. Herein, we utilize cellulose decorated with Azo and gold nanorods (AuNRs) of different aspect ratio (AR) to present how material design can affect the performance of photoresponsive systems. The size-dependent catalytic effect of AuNRs is manifested during UV-vis and dark isomerization of Azo with rate constants inversely related to the AR. Comparison of spectroscopic and microscopic data indicates LSPR shifts and subtle shortening of AuNRs upon repeated photoswitching (2.513-2.505 AR decrease for one of the samples), thus confirming electron and energy transfer as catalytic enhancement mechanisms. Finally, Azo dark isomerization rate constants are juxtaposed with structural parameters of the material derived from AR, including total surface area or number of nanoparticles. The average relative differences between structural parameters equal 22% if AuNRs with highest versus lowest AR are compared, while the kinetic differences reach 50% on average. These results indicate that the observed size effect is a convolution of several structural descriptors.