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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Tuning Excited-State Charge Transfer Character in Cofacial Core-Substituted Perylenediimide Dimers

Understanding the interplay between excimer formation and symmetry-breaking charge separation is important for optimizing charge separation in organic photovoltaic materials. To explore this connection, we synthesized four 1,6,7,12-tetrakis( p -X-phenoxy)perylene-(3,4:9,10)-bisdicarboximide cofacially stacked dimers, where X = MeO, tert -butyl, Br, and CF 3 . Steady-state spectroscopy reveals H-type aggregation and excimer formation in all four dimers, while transient absorption spectroscopy shows relatively small changes in their excited-state absorptions. However, time-resolved fluorescence (TRF) spectroscopy shows that relaxation occurs from an initial Frenkel exciton-dominated excimer state to one in which charge transfer (CT) character contributes. Relaxation to the lower-lying state with CT character is attributed to a combination of structural and charge distribution changes elicited by varying the substituents. Finally, this study illustrates how subtle changes in charge distribution and structure can combine to influence the excited state dynamics that influence charge separation in molecular dimers.

fluorescence↗
DOE OSTI2020

Trends in Carbon, Oxygen, and Nitrogen Core in the X-ray Absorption Spectroscopy of Carbon Nanomaterials: A Guide for the Perplexed

Successful deployment of carbon nanomaterials in many applications, such as sensing, energy storage, and catalysis, relies on the selection, synthesis, and tailoring of the surface properties. Predictive analysis of the behavior is difficult without detailed knowledge of the differences between various carbon nanomaterials and their surface functionalization, thus leaving the selection process to traditional trial-and-error work. The present characterization fills this knowledge gap for carbon nanomaterial surface properties with respect to chemical states and functionalization. We present an overview of the chemical trends that can be extracted from soft X-ray absorption spectroscopy (XAS) spectra on an extended set of nonideal carbon nanomaterials as a function of sp 2 bonded carbon and bond ordering. In particular, the surface chemical state, the presence of long-range order in the carbon matrix, and a qualitative estimation of the amount of oxygen and nitrogen and their respective functional group formation on the material surface, together with the detailed material fabrication parameters, are reported. The results expand our understanding of carbon nanomaterial functionalization, which can support material selection in practice, provided that the specifications of the application are known.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗