Dye-nanocrystal systems are relevant to applications in photovoltaics, photocatalysis, and spintronics that rely on an understanding of electron transfer dynamics to optimize their performance in devices. To understand electron transfer in dye-In₂O₃systems, we synthesized two organic dyes, (E)-2-cyano-3-(5-(4-(diethylamino)phenyl)thiophen-2-yl)acrylic acid (1) and (E)-2-cyano-3-(5-(4-(diethylamino)phenyl)furan-2-yl)acrylic acid (2), and bound them to colloidal monodisperse oleate-capped In₂O₃nanocrystals made using a continuous growth method. Equilibrium binding constants were evaluated using fluorescence quenching and modeled with Langmuir adsorption isotherms. Subsequent ultrafast transient absorption measurements established that the quenching occurred through excited state electron transfer. The binding constants were 5.4(2.1) x 10⁶M^-1 and 3.2(1.9) x 10⁶M^-1 and the electron transfer time constants were 1.83 (0.03) and 1.41 (0.05) ps for 1 and 2 bound to In₂O₃, respectively. The binding constants of 1 and 2 are similar to those obtained in a previous study with ZnO. The electron transfer time constants on In₂O₃ are ~8-9 times than on ZnO which may be attributed to the higher density of acceptor states in In₂O₃and differences in electronic coupling. Interestingly, the extent of quenching was found to be sensitive to the homogeneity of the nanocrystals. More uniform nanocrystals with well-defined, cubic faces as shown in the figure resulted in less quenching, which may be attributed to the possible formation of robust, self-assembled oleate monolayers inhibiting dye access to the In₂O₃.

Mik Patel

Appearances