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Recently, white polymer light-emitting diodes (WPLEDs) have received considerable attention because of their potential utilization in display and lighting applications via low-cost solution processing. One common approach to obtaining white emission from polymer LEDs is to use blends as emissive layers, such as polymer/polymer blends [1][2][3][4][5][6] or polymer/ small-molecule blends. [7][8][9][10][11][12][13][14][15][16] Although high electroluminescence (EL) efficiencies have been achieved, WPLEDs based on blend systems suffer from bias-dependent EL spectra and intrinsic phase separation during long-term device operation. Another approach to WPLEDs is the use of a single polymer as the emissive layer. [17][18][19] Together, blue emission from the polymer itself and orange emission from an aggregate/excimer/exciplex give white emission. Although phase separation is completely prevented, WPLEDs based on this strategy suffer from low EL efficiencies. Our group has proposed a novel strategy for a white electroluminescent single polymer, which involves incorporating an orange-light-emitting unit into a blue-emitting polymer host. [20][21][22][23][24][25] WPLEDs of this design have the great advantages of high EL efficiencies, bias-independent EL spectra, and no phase separation. We also found that the EL efficiencies of white polymers could be improved by either enhancing the PL quantum efficiency of the orange-emitting species [22] or attaching an orange-emitting species to the side chain of a blueemitting polymer backbone.[23]In all of our white single polymers, the blue-emitting species is polyfluorene (PF). Moreover, the aforementioned efficient WPLEDs based on blends also employ PF as the blue-emitting material; however, as a blue electroluminescent polymer PF suffers from two drawbacks: i) the PL quantum efficiency of PF in solid films is low (U PL = 0.55) [27,28] because of the interaction of polymer chains, and ii) the emission spectrum of PF lies in the deep-blue region, to which human eyes are insensitive, and limits the luminous efficiency of the white emission. Hence, we believe that the blue-emitting species is the bottleneck for the EL efficiency of white electroluminescent polymers and devices. Our group has reported a highly efficient blue-emitting polymer of a dopant/host system, in which a light-blue-emitting dimethylamino naphtalimide (DMAN) unit (model compound 4-dimethylamino-9-decyl-1,8-naphthalimide (MC-B1), see Supporting Information) is attached to the side chain of deep-blue-emitting PF (PFB5, see Scheme 1).[29] This polymer exhibits a much higher EL efficiency than PF because its emission dominantly originates from the highly fluorescent, dispersed DMAN unit (U PL = 0.84), and because its EL spectrum is partially red-shifted compared with that of PF (ca. 30 nm). In this Communication, we report how we have replaced PF by a DMAN-containing PF as the blue-emitting species in a white-emitting single polymer, with the aim of improving the EL efficiencies of white-emitting single polymers by...

Binary coinage metal clusters can show a significantly different enhancement in surface-enhanced Raman scattering (SERS) from that of pure element clusters, owing to their tunable surface plasmon resonance energies affected by the composition and atomic ordering. Yet, the tunability by composition requires a deep understanding in order to further optimize the SERS-based detection technique. Here, to fill this deficiency, we conducted detailed analyses of the SERS of pyridine adsorbed through N-Ag bonding on the homonuclear diatomic metal cluster Ag2 and heteronuclear diatomic metal clusters of AuAg and CuAg, as well as the involved charge transfer under an intracluster excitation, based on calculations using time-dependent density functional theory with a short-time approximation for the Raman cross-section. We find that although the SERS enhancements for all complexes can reach the order of 10(3)-10(4), the corresponding wavelengths used for SERS excitation are significantly different. Our molecular orbital analysis reveals that the complexes based on heteronuclear metal clusters can produce varied electronic transitions owing to the polarization between different metal atoms, which tune the SERS enhancements with altered optical properties. Our analyses are expected to provide a theoretical basis for exploring the multi-composition SERS substrates applicable for single molecular detection, nanostructure characterization, and biological molecular identification.