Scientists unlock fluorescence control in nitro-doped organic compounds
Researchers have identified how the position of nitro groups on aromatic molecules determines whether they glow or go dark—a finding with immediate applications for display technology, medical imaging, and optical sensors. By mapping the quantum mechanics of electron flow, the team shows how to preserve brightness in materials that typically lose it, opening new design pathways for commercial light-emitting devices.
Originaltitel: The interplay of intersystem crossing and internal conversion in quadrupolar tetraarylpyrrolo[3,2-<em>b</em>]pyrroles
<p>Adding nitro groups to aromatic compounds usually quenches their fluorescence via intersystem crossing (ISC) or internal conversion (IC). Herein, we investigated centrosymmetric 1,4-dihydropyrrolo[3,2-b]pyrroles linked to variously substituted nitro-heteroaryls. A 1,4-orientation of the nitro substituent versus the electron rich 1,4-dihydropyrrolo[3,2-b]pyrrole core invokes a strong fluorescence in non-polar solvents and intense two-photon absorption while a 1,3-orientation of push-pull substituents results in a dramatic hypsochromic shift of absorption, weak, bathochromically shifted emission and weak two-photon absorption. The combined experimental and computational study indicates that the primary responsible factors are: (1) the difference in electron density distribution in the LUMO; (2) the difference in mu 10. IC is a dominant mechanism of non-radiative dissipation of energy in all these dyes but as long as the distribution of electron density within the HOMO and LUMO is delocalized on the 1,4-dihydropyrrolo[3,2-b]pyrrole core as well as on the nitroaromatic moieties its rate is slower than the fluorescence rate in non-polar solvents.</p>