We investigate amplified energy transfer in conjugated polymer nanoparticles (CPNs or Pdots) by studying both fluorescence quenching of CPN donors and the sensitization of reactive dye acceptors. By delivering excitation energy to dye dopants via a combination of Forster energy transfer and exciton diffusion, CPNs act as powerful light-harvesting antennae. This phenomenonamplified energy transferis used to sensitize dye dopants, producing a higher concentration of the dye's excited state than would be observed upon direct excitation. Here, we study CPN sensitization of a low-efficiency photochemical reaction to determine the CPN size and dye loading that yield optimized outputs in the form of energy transfer efficiency, the antenna effect (AE), and reaction duration. Our model system is the cycloreversion reaction of a diarylethene (DAE) photochrome as the dye dopant and CPNs of the conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-thiadiazole] as the sensitizer. In their visible-absorbing form, DAE dyes are localized on the particle surface and are effective fluorescence quenchers of 15, 20, and 26 nm diameter CPNs. Quenching is most efficient for the smallest particles, and high dye loadings are necessary to offset reduced efficiency as CPN size increases. Our photokinetic studies of DAE acceptors demonstrate the crucial importance of dye loading: both energy transfer efficiency and the AE show abrupt declines when the dye concentration is increased beyond a critical threshold. We find that CPNs with a 15 nm diameter exhibit the most efficient energy transfer (99−100%) and the largest AE (32) of the CPNs studied. For CPNs of all sizes and dye loadings, a photoselection phenomenon reveals that the energy-transferaccepting ability of the DAE dyes varies tremendously within the dye ensemble. These findings are used to develop design recommendations for CPN sensitizers.

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Electrocatalytic water splitting presents an exciting opportunity to produce environmentally benign hydrogen fuel to power human activities. Earth-abundant Ni 5 P 4 has emerged as an efficient catalyst for the hydrogen evolution reaction (HER), and its activity can be enhanced by admixing synergistic metals to modify the surface affinity and consequently the kinetics of HER. Computational studies suggest that the HER activity of Ni 5 P 4 can be improved by Zn doping, causing a chemical pressure-like effect on Ni 3 hollow sites. Herein, we report a facile colloidal route to produce Ni 5−x Zn x P 4 nanocrystals (NCs) with control over structure, morphology, and composition and investigate their composition-dependent HER activity in alkaline solutions. Ni 5−x Zn x P 4 NCs retain the hexagonal structure and solid spherical morphology of binary Ni 5 P 4 NCs, with a notable size increase from 9.2−28.5 nm for x = 0.00−1.27 compositions. Elemental maps affirm the homogeneous ternary alloy formation with no evidence of Zn segregation. Surface analysis of Ni 5−x Zn x P 4 NCs indicates significant modulation of the surface polarization upon Zn incorporation, resulting in a decrease in Ni δ+ and an increase in P δ− charges. Although all compositions followed a Volmer−Heyrovsky HER mechanism, the modulated surface polarization enhances the reaction kinetics, producing lower Tafel slopes for Ni 5−x Zn x P 4 NCs (82.5−101.9 mV/dec for x = 0.10−0.84) compared to binary Ni 5 P 4 NCs (109.9 mV/dec). Ni 5−x Zn x P 4 NCs showed higher HER activity with overpotentials of 131.6−193.8 mV for x = 0.02− 0.84 in comparison to Ni 5 P 4 NCs (218.1 mV) at a current density of −10 mA/cm 2 . Alloying with Zn increases the material's stability with only a ∼10% increase in overpotential for Ni 4.49 Zn 0.51 P 4 NCs at −50 mA/cm 2 , whereas a ∼33% increase was observed for Ni 5 P 4 NCs. At current densities above −40 mA/cm 2 , bimetallic NCs with x = 0.10, 0.29, and 0.51 compositions outperformed the benchmark Pt/C catalyst, suggesting that hexagonal alloyed Ni 5−x Zn x P 4 NCs are excellent candidates for practical applications that necessitate lower HER overpotentials at higher current densities.