Synthesis, Photophysical, Photochemical, and Computational Studies of Coumarin-Labeled Nicotinamide Derivatives

Abstract

The syntheses and photophysical/photochemical properties of two amide-tethered coumarin-labeled nicotinamides are described. Photochemical studies of 6-bromo-7-hydroxycoumarin-4-ylmethylnicotinamide (BHC-nicotinamide) revealed an unexpected solvent effect. This result is rationalized by computational studies of the different protonation states using TD-DFT with the M06L/6-311+G** method with implicit and explicit solvation models. Molecular orbital energies responsible for the λ(max) excitation show that the functionalization of the coumarin ring results in a strong red-shift from 330 to 370 nm when the pH of solution is increased from 3.06 to 8.07. From this MO analysis, a model for solvent interactions has been proposed. The BHC-nicotinamide proved to be photochemically stable, which is also interpreted in terms of NBO calculations. The results provide a set of principles for the rational design of either photostable labeling reagents or photolabile cage compounds.

Photophysical insights and guidelines for blue “turn‐on” fluorescent probes for the direct detection of nitric oxide (NO•) in biological systems

“…This second, bathochromically shifted band in CB1‐5 could result from a solvent‐induced ground state deprotonation. A similar solvent dependence of λ max has been described for 3‐hydroxyflavone and coumarin‐substituted nicotinamides . The extent of the solvochromatic shift correlates with the pK a for CB1‐5 .…”

“…A similar solvent dependence of λ max has been described for 3-hydroxyflavone [26] and coumarin-substituted nicotinamides. [27] The extent of the solvochromatic shift correlates with the pK a for CB1-5. In the case of the least acidic coumarin derivative CB1, this effect is only observed with the most polar solvent DMSO, while the strongly acidic CB5 interacts with DMSO, MeOH, MeCN, and even Et 2 O.…”

Structure–activity relationship studies of 4-methylcoumarin derivatives as anticancer agents

“…Compound 25 was synthesized by following the reported multistep procedure and was then acetylated to yield compound 26 (Reszka et al, 2010). To synthesize compound 27, commercially available 4-bromoresorcinol was reacted with ethyl-4-bromoacetoacetate via the literature procedure (Bourbon et al, 2012). The compound 27 is novel and the data are reported for the first time ( Table 1).…”

Red Emitting Coumarins: Insights of Photophysical Properties with DFT Methods

“…Towards this end, in this paper a complete focus has been laid to rationalise the practical observations with the help of ab initio methods. There are many such reports investigating the photophysics of the coumarins with the help of DFT [58][59][60][61][62][63][64]. The coumarin molecules taken up for the studies were relatively smaller (30-40 atoms).…”