Ab initio study of the solvent H-bonding effect on ESIPT reaction and electronic transitions of 3-hydroxychromone derivatives

Abstract

The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules. To examine the effect of the H-bond on the ESIPT reaction, the absorption and emission wavelengths as well as the energies of the different states that intervene during these electronic transitions were calculated in acetonitrile, ethanol and methanol. The calculated positions of the absorption and emission wavelengths in various solvents were in excellent agreement with the experimental spectra, validating our approach. We found that in DMAF, the hydrogen bonding with protic solvents makes the ESIPT reaction energetically unfavourable, which explains the absence of the ESIPT tautomer emission in protic solvents. In contrast, the excited tautomer state of FHC remains energetically favourable in both aprotic and protic solvents. Comparing our calculations with the previously reported timeresolved fluorescence data, the ESIPT reaction of DMAF in aprotic solvents is reversible because the emitting states are energetically close, whereas in FHC, ESIPT is irreversible because the tautomer state is below the corresponding normal state. Therefore, the ESIPT reaction in DMAF is controlled by the relative energies of the excited states (thermodynamic control), while in FHC the ESIPT is controlled probably by the energetic barrier (kinetic control).

Electronic transitions and ESIPT kinetics of the thienyl-3-hydroxychromone nucleobase surrogate in DNA duplexes: a DFT/MD-TDDFT study

“…This behaviour suggests an electron delocalisation from the thienyl ring and proton donor oxygen O17 to the proton acceptor O16, as already mentioned in other 3HC derivatives. 42 This electron delocalisation is thought to render O17H more acidic (as supported by the Mulliken charge variation, Dq ¼ +0.06 a.u) and O16 more basic (Dq ¼ À0.06 a.u), thus favouring the ESIPT. Interestingly, the distance between the transferring proton and the carbonyl oxygen is 1.976 A, thus supporting the formation of an intramolecular H-bond ( Fig.…”

“…Concomitantly, the magnitude of the molecular dipole moment varies from 3.94 D in the ground state to 7 D in the S 1 excited state. A charge displacement from an aryl group is common for ESIPT dyes, 42,43 and is responsible of the strongly increased dipole moment of N* as compared to N. 44 To understand the mechanism that governs the ESIPT reaction in acetonitrile, we have calculated the energies of the transition state (TS) and all the other states that likely intervene in the photophysics of M (Fig. 2).…”

“…These results highlight the key importance of specic intermolecular H-bonding with water molecules to account for the photophysics of M in aqueous media, a behaviour already observed with other 3HC derivatives. 42 To get insight into the kinetics of the ESIPT reaction in water, the conformation and energy of the transition state (TS) were calculated. The energy of the TS state was found 0.55 eV above the S NH 1 (R) state, so that the activation barrier to the ESIPT reaction is very high.…”

Development of environmentally sensitive fluorescent and dual emissive deoxyuridine analogues

“…The blue shift can be explained by the formation of an H-bond between the 3phenoxide oxygen in the T* state and the donor proton in the solvent. 52,53 All the three compounds displayed an increase in the I N* /I T* ratio by rising solvent polarity and H-bond donor strength (Table 2, Fig. 4).…”

“…52,56,60 This latter involves specific H-bonding interactions of water with the electron rich oxygens of 4-carbonyl and phenoxide of 3HC (Scheme 5). As a result, the N* form exists in equilibrium with a protonated N*-H form, in which intermolecular H-bonding of the 4-carbonyl with water inhibits the ESIPT process.…”