ADDITION OF FERROCENE DERIVATIVES TO THE SURFACE OF QUANTUM-CONFINED CADMIUM-SULFIDE CLUSTERS - STEADY-STATE AND TIME-RESOLVED PHOTOPHYSICAL EFFECTS

The effect of substituted ferrocene complexes on the surface of quantum-confined (Q) cadmium sulfide clusters in inverse micelles was examined by steady-state and time-resolved photoluminescence (PL) spectroscopy. Addition of (dimethylamino)methylferrocene (DMAMF) to Q-CdS enhanced cluster PL peak areas by 120%, in contrast to the carboxylic acid derivatives ferrocenecarboxylic acid (FCA) and ferrocenedicarboxylic acid (FDCA), which quenched PL by 60% and 80%, respectively. Unsubstituted ferrocene, hydroxymethylferrocene, and ferrocenecarboxaldehyde had no effect on the PL intensity of these clusters. The induced PL changes fit a Langmuir-type adsorption isotherm from which formation constants for the Q-CdS:surface adducts were calculated. The average log K(f) value calculated for DMAMF adsorption was 4.12. FCA addition gave an average log K(f) of 5.17, and the average log K(f) value for FDCA addition was 6.14. Binding of the amino group of DMAMF to shallow trap states arising from Cd2+ sites is postulated as its mechanism for PL enhancement, while the quenching mechanism for FCA and FDCA is attributed to proton transfer induced from ionization of the acids in the micelle water pools. "Competition" experiments show that quenching by the carboxylic acid derivatives can be reversed by the addition of amino-substituted ferrocene, and vice versa. The results also suggest a possible DMAMF-induced surface reconstruction. These steady-state observations are supported by measurements of the PL decay via subnanosecond time-correlated single photon counting. Fits of the decay monitored at 620 nm to a modified stretched exponential model indicate that the average distributed decay time <tau(2)> of nanosecond duration can be either lengthened or shortened, depending on the nature of the added ferrocene.