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Alkali Blues: Blue‐Emissive Alkali Metal Pyrrolates
Author(s) -
Back Oliver,
Förster Christoph,
Basché Thomas,
Heinze Katja
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201806103
Subject(s) - chemistry , alkali metal , deprotonation , chromophore , excited state , intramolecular force , photochemistry , fluorescence , moiety , inorganic chemistry , ion , stereochemistry , organic chemistry , physics , quantum mechanics , nuclear physics
2‐Iminopyrroles [H t Bu L, 4‐ tert ‐butyl phenyl(pyrrol‐2‐ylmethylene)amine] are non‐fluorescent π systems. However, they display blue fluorescence after deprotonation with alkali metal bases in the solid state and in solution at room temperature. In the solid state, the alkali metal 2‐imino pyrrolates, M( t Bu L), aggregate to dimers, [M( t Bu L)(NCR)] 2 (M=Li, R=CH 3 , CH(CH 3 )CNH 2 ), or polymers, [M( t Bu L)] n (M=Na, K). In solution (solv=CH 3 CN, DMSO, THF, and toluene), solvated, uncharged monomeric species M( t Bu L)(solv) m with N , N ′‐chelated alkali metal ions are present. Due to the electron‐rich pyrrolate and the electron‐poor arylimino moiety, the M( t Bu L) chromophore possesses a low‐energy intraligand charge‐transfer (ILCT) excited state. The chelated alkali cations rigidify the chromophore, restricting intramolecular motions (RIM) by the chelation‐enhanced fluorescence (CHEF) effect in solution and, consequently, switch‐on a blue fluorescence emission.