Ground-State Tautomerism and Excited-State Proton Transfer in 7-Hydroxy-4-methyl-8-((phenylimino)methyl)-2H-chromen-2-one as a Potential Proton Crane

Abstract

The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isomerization around the azomethine bond as in other structurally similar Schiff bases. The studied compound is not suitable for bistable tautomeric switching, where long-range PT occurs, due to the difficult enolization of the coumarin carbonyl group.

N^N^C-Cyclometalated rhodium(iii) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

“…the ability of compounds with identical molecular formulae to exist in spatially different forms is one of the most fundamental ideas in chemistry. [1][2][3] Revealing the impact of isomerism on crystal structures, [4][5][6][7][8][9][10][11][12] and chemical properties, [13][14][15][16][17][18][19][20][21] as well as physical [22][23][24][25][26][27][28][29][30][31][32][33][34] and biological properties [35][36][37][38][39] is of particular importance for establishing structure-property relationships which pave the way toward the more predictable design of substances with desirable properties. Despite various kinds of constitutional and configurational isomerism of metal complexes being well known, 40 ligand isomerism, which belongs to constitutional isomerism, is documented in literature to a considerably lesser extent than other types of the isomerism of complexes.…”