Pyrazole, Imidazole, and Isoindolone Dipyrrinone Analogues: pH-Dependent Fluorophores That Red-Shift Emission Frequencies in a Basic Solution.

Autor: Benson N; Department of Physical and Life Sciences , Nevada State College , Henderson , Nevada 89002 , United States., Suleiman O; Department of Chemistry , University of Nevada , Reno , Nevada 89557 , United States., Odoh SO; Department of Chemistry , University of Nevada , Reno , Nevada 89557 , United States., Woydziak ZR; Department of Physical and Life Sciences , Nevada State College , Henderson , Nevada 89002 , United States.
Jazyk: angličtina
Zdroj: The Journal of organic chemistry [J Org Chem] 2019 Sep 20; Vol. 84 (18), pp. 11856-11862. Date of Electronic Publication: 2019 Sep 05.
DOI: 10.1021/acs.joc.9b01708
Abstrakt: Dipyrrinones are nonfluorescent yellow-pigmented constituents of bilirubin that undergo Z to E isomerization when excited with UV/blue light. Mechanical restriction of the E/Z isomerization process results in highly fluorescent compounds such as N , N -methylene-bridged dipyrrinones and xanthoglows. This manuscript describes the first examples of dipyrrinone analogues, which exhibit fluorescence without covalently linking the pyrole-pyrrolidine nitrogen atoms. Instead these analogues restrict E/Z isomerization through intramolecular hydrogen bonding, resulting in mild to moderately fluorescent compounds (Φ F = 0.01-0.30). Further, in basic solutions (pH > 12), the dipyrrinone analogues readily deprotonate and absorption/emission profiles of the fluorophores red-shifts by 10-49 nm. Directly from commercial materials, 10 analogues were prepared in 41-96% yields in one step. To estimate the capacity of which intramolecular hydrogen bonding has upon restricting the E/Z isomerization process, conformational energies of all analogues, in both the protonated and deprotonated species, were explored by using quantum-mechanical density functional theory (DFT) and time-dependent DFT calculations. The computed strengths of the intramolecular hydrogen bonds are related to the barriers of rotation about the 5-6 bond and both correlate with the experimentally measured fluorescence quantum yields.
Databáze: MEDLINE