Excited-State Proton Transfer in 7-Hydroxy-4-methylcoumarin along a Hydrogen-Bonded Water Wire

Abstract

TDDFT, RI-CC2, and CIS calculations have been performed for the nondissociative excited-state proton transfer (ESPT) in the S1 state of 7-hydroxy-4-methylcoumarin (7H4MC) along a H-bonded water wire of three water molecules bridging the proton donor (OH) and the proton acceptor (C[double bond]O) groups (7H4MC.(H2O)3). The observed structural reorganization in the water-wire cluster is interpreted as a proton-transfer (PT) reaction along the H2O solvent wire. The shift of electron density within the organic chromophore 7H4MC due to the optical excitation appears to be the driving force for ESPT. All the methods used show that the reaction path occurs in the 1pipi* state, and no crossing with a Rydberg-type 1pisigma* state is found. TDDFT and RI-CC2 calculations predict an exoergic reaction of the excited-state enol-to-keto transformation. The S1 potential energy curve reveals well-defined Cs minima of enol- and keto-clusters, separated by a single barrier with a height of 17-20 kcal/mol. After surmounting this barrier, spontaneous PT along the water wire is observed, leading without any further barrier to the keto structure. The TDDFT and RI-CC2 methods appear to be reliable approaches to describe the energy surfaces of ESPT. The CIS method predicts an endoergic ESPT reaction and an energy barrier, which is too high.

Excited-State Hydrogen Atom Transfer Reaction in Solvated 7-Hydroxy-4-methylcoumarin

“…Therefore, the enol−keto excited-state process corresponds to a HT, not a PT. This is in good agreement with the CIS/SVPD population analysis done by Georgieva et al 43 Table 2. Table 2 indicates that the S 0 tautomerization of C456:3H 2 O in the gas phase is characterized by a high activation energy (0.87 eV), whereas the S 1 state reaction proceeds with a low activation energy (0.23 eV).…”

“…Georgieva et al extended the investigation by studying the PT reaction in C456 along a H-bonded water wire of three water molecules using TDDFT, RI-CC2, and singly excited configuration interaction (CIS) calculations. 43 The calculations suggest the possibility of HT/PT from the enol to the keto form in the excited state. All of the methods used predict that the reaction path occurs in the π−π* state, and no crossing with a Rydberg-type πσ* state was found.…”

Synthesis, characterization, and antimicrobial activity of some new coumarin derivatives

“…Moreover, 7-amino 4-methyl coumarin is also used as laser dye and intermediate for the synthesis of bioactive compounds (Nowakowska et al, 2001) and the 4-methylcoumarin derivatives present in various naturally occurring compounds, are known to exhibit a wide range of biological and pharmaceutical activities (Ramesh and Raghunathan, 2008). In addition, coumarin moieties containing hydrazide and sulfonamide groups act as anti-malarial, antiviral activity, anti-HIV, and anticancer agents (Havaldar and Patil, 2008;Hwu et al, 2008;Azizian et al, 2008;Georgieva et al, 2007).…”

Investigation of the structures and electronic spectra of two coumarins with heterocyclic substituents through TD-DFT calculations

“…The time-dependent density functional theory (TD-DFT) has been applied to study various 7-aminocoumarins [29][30][31][32][33][34][35][36][37][38][39][40][41][42]. In 2002, Cave et al [29,30] performed a detailed theoretical study on several coumarins using different electronic structure methods and concluded that the TD-DFT method was a powerful tool for treating the spectroscopy of 7-aminocoumarins.…”

“…In 2002, Cave et al [29,30] performed a detailed theoretical study on several coumarins using different electronic structure methods and concluded that the TD-DFT method was a powerful tool for treating the spectroscopy of 7-aminocoumarins. More recently, the spectra of a series of coumarins [31][32][33][34][35][36][37][38][39][40][41][42] the TD-DFT method has also been used to study the electronic spectra of the 2,2 0 -bipyridine derivatives [43], the fluorescent material A31 [44] and the TEMPO [45].…”