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

Abstract

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.

Wavelength-Dependent Photochemistry and Biological Relevance of a Bilirubin Dipyrrinone Subunit

“…32 The isomerization can also be restricted by linking pyrrole's nitrogen atoms through a methylene or carbonyl bridge, 34−40 a difluoroboryl group as in the case of BODIPY derivatives, 41,42 or via intramolecular hydrogen bond in certain dipyrrinone analogues. 43 The photochemistry of simple dipyrrinones and their derivatives, such as benzalpyrrolinones 44 or other heterocyclic analogues 45,46 that undergo only E,Z photoisomerization, has been studied. 32,44−46 To the best of our knowledge, mechanistic investigations of the intramolecular photocyclization of dipyrrinone derivatives, analogous to the photochemical conversion of BR to lumirubin (Scheme 1), remain largely unexplored.…”

Exploration of Novel TOSMIC Tethered Imidazo[1,2-a]pyridine Compounds for the Development of Potential Antifungal Drug Candidate.

“…23 (1 H, s), 7.96 -7.88 (2 H, m), 7.48 (1 H, d, J = 2.8 Hz), 7.34 -7. 23 (2 H, m), 7.00 (`1 H, dd, J = 4.0, 2.8 Hz), 6.80 (1 H, dd, J = 3.8, 1.2 Hz), 4.91 (1 H, s), 2.39 (3 H, s), 1.23 (2 H, s). 13…”

“…Besides their biological application the core also has many applications in electronic devices (5). Additionally, these N-heterocyclic often form a complex π-conjugated system and consequently serve as uorophores (6). Therefore, owing to their robust applications the development of Nitrogen-rich novel heterocyclic compounds is highly desirable.…”

The crystal structure of 2-[(S)-1-(naphthalen-1-yl)ethyl]-2,3,7,7a- tetrahydro-3a,6-epoxyisoindol-1(6H)-one, C19H20NO2

“…The class of chemical compounds the title compound belongs to has members that are important intermediates for the synthesis of isoindolinone compounds and can be used to prepare fluoresce and biologically active molecules [3,4]. They can participate in the synthesis of alkaloids Aspernidine A and Aspernidine B for the preparation of anticancer drugs and antiviral drugs [5,6].…”