Beyond “Mega”: Origin of the “Giga” Stokes Shift for Triazolopyridiniums

Abstract

Over the past decade, fluorophores that exhibit "mega" Stokes shifts, defined to be Stokes shifts of greater than 100 nm, have gained considerable attention due to their potential technological applications. A subset of these fluorophores have Stokes shifts of at least 10,000 cm −1 , for whom we suggest the moniker "giga" Stokes shift. The majority of "giga" Stokes shifts reported in the literature arise from the twisted intramolecular charge transfer mechanism, but this mechanism does not fit empirical characterization of triazolopyridinium (TOP). This observation inspired a density functional theory (DFT) and time-dependent DFT study of TOP, and several related fluorophores, to elucidate the novel photophysical origin for the "giga" Stokes shift of TOP. The resulting computational models revealed that photoexcitation of TOP yields a zwitterionic excited state that undergoes significant structural relaxation prior to emission. Most notably, TOP has two orthogonal moieties in the ground state that adopt a coplanar geometry in the excited state. According to Huckel's rule, both the heterocycle and phenyl moieties of TOP should be aromatic in an orthogonal ground state. However, according to Baird's rule, these individual moieties should be anti-aromatic in the excited state. By relaxing to a coplanar conformation in the excited state, TOP likely forms a single aromatic system consisting of both the heterocycle and phenyl moieties.

PyrAtes: Modular Organic Salts with Large Stokes Shifts for Fluo‐rescence Microscopy

“…Figure 4A outlines a brief comparison of Stokes shifts of representative PyrAtes (bottom) with selected known fluorophores (top). [28,29,[49][50][51][52][53][54][55][56][57][58] Change at the ground-and excited-state energy profiles of certain fluorescent probes in response to environment (e.g., solvent [59][60][61] or pH [62] ) has been an attractive means in proteomics for the study of protein-protein interactions (PPIs) or protein folding, [63] as well as in the study of lipid dynamics of cellular membranes, for diagnostics in medicine, [62,64] and for selective organelle imaging. [65] As a canonical probe, we examined the solvatochromic behavior of PyrAte 7 a (Figure 4B).…”

“…One of the most significant findings of this study is that the synthesis of PyrAtes is a straightforward process and delivers fluorophores with large Stokes shifts (typically >135 nm). Figure 4A outlines a brief comparison of Stokes shifts of representative PyrAtes (bottom) with selected known fluorophores (top) [28,29,49–58] …”

PyrAt‐Verbindungen: Modulare organische Salze mit großen Stokes‐Verschiebungen für die Fluoreszenzmikroskopie

“…Eine der wichtigsten Erkenntnisse aus dieser Studie ist, dass die Synthese von PyrAt‐Verbindungen ein unkomplizierter Prozess ist und Fluorophore mit großen Stokes‐Verschiebungen (typischerweise >135 nm) liefert. Abbildung 4A zeigt einen kurzen Vergleich der Stokes‐Verschiebungen von repräsentativen PyrAt‐Verbindungen (unten) mit ausgewählten, literaturbekannten Fluorophoren (oben) [28,29,49–58] …”

“…Abbildung 4A zeigt einen kurzen Vergleich der Stokes-Verschiebungen von repräsentativen PyrAt-Verbindungen (unten) mit ausgewählten, literaturbekannten Fluorophoren (oben). [28,29,[49][50][51][52][53][54][55][56][57][58] Die Änderung des Energieprofils im Grundzustand und im angeregten Zustand bestimmter fluoreszierender Sonden als Reaktion auf die Umgebung (z. B. Lösungsmittel [59][60][61] oder pH-Wert [62] ) ist ein attraktives Mittel in der Proteomik zur Untersuchung von Protein-Protein-Wechselwirkungen (PPIs) oder der Proteinfaltung, [63] sowie zur Untersuchung der Lipiddynamik zellulärer Membranen, zur Diagnostik in der Medizin, [62,64] oder zur selektiven Darstellung von Organellen.…”

Evaluating the isomeric effects of donors on the structures and photophysical properties of donor–acceptor–π bridge–donor (D1–A–π–D2) prototype fluorophores

“…In particular, small organic fluorophores with a donor-acceptor (D-A) architecture have received considerable interest due to their distinct and highly tunable optical properties. [1][2][3][4] Much effort has been made to design and synthesize new D-A organic fluorophores by changing the types of donor and acceptor. [5][6][7][8] These reported studies showed that changing the nature of the donor and acceptor would affect the properties of D-A organic fluorophores.…”