Morphology-Preserving Sensitization of ZnO Nanorod Surfaces via Click-Chemistry

Films of ZnO nanorods grown by chemical vapor deposition were functionalized with a chromophore in a stepwise process that preserves the surface morphology. In the first step, the ZnO nanorods were functionalized by exposure to prop-2-ynoic acid (propiolic acid) in vacuum, which did bind through the COOH group leading to a ZnO surface functionalized with ethyne moieties (ethyne/ZnO). In the second step, 9-(4-azidophenyl)-2,5-di-tert-butylperylene (DTBPe-Ph-N₃) was reacted with the ethyne/ZnO surface via copper-catalyzed azide-alkyne click reaction (CuAAC) in solution to form the DTBPe-functionalized surface (DTBPe/ZnO). The ZnO morphology was preserved after each step, as demonstrated by scanning electron microscopy (SEM). Each step was probed by X-ray photoelectron spectroscopy (XPS), and transient absorption spectroscopy (TA) of the resulting DTBPe/ZnO surface shows interfacial electron transfer following visible light excitation. As expected, attempts to bind the reference compound 1-(4-(8,11-ditert-butylperylen-3-yl)-phenyl)-1H-1,2,3-triazole-4-carboxylic acid (DTBPe-Ph-Tz-COOH) directly from solution lead to etched surfaces (confirmed by SEM) and undefined binding modes (confirmed by TA).