Highly Polarized Coumarin Derivatives Revisited: Solvent-controlled Competition Between Proton Coupled Electron Transfer and Twisted Intramolecular Electron Transfer.

Highly Polarized Coumarin Derivatives Revisited: Solvent-controlled Competition Between Proton Coupled Electron Transfer and Twisted Intramolecular Electron Transfer.
Chemistry. 2020 Mar 25;:
Authors: Morawski O, Kielesiński Ł, Gryko DT, Sobolewski A
Abstract
Linking a polarized coumarin unit with an aromatic substituent via an amide bridge results in weak electronic coupling affecting the intramolecular electron transfer (ET) process. As a result of this, interesting solvent-dependent photophysical properties can be observed. In polar solvents, electron transfer in coumarin derivatives of this type induces a mutual twist of electron-donating and electron-accepting molecular units (TICT process) that opens radiationless decay processes (internal conversion). In the dyad with the strongest intramolecular hydrogen bond, the planar form is stabilized so twisting can only occur in highly polar solvents, whereas fast proton coupled electron transfer (PCET process) occurs in non-polar n-alkanes. The kPCET rate constant decreases linearly with the fluorescence maximum energy in different solvents. This observation is explained in terms of competition between electron and proton transfer from a highly polarized (~15 D) and fluorescent locally-excited (1LE) state to a much less polarized (~4 D) charge-transfer (1CT) state, a unique occurrence. Photophysical measurements performed for a family of related coumarin dyads together with results ...

Source: Chemistry - March 24, 2020 Category: Chemistry Authors: Morawski O, Kielesiński Ł, Gryko DT, Sobolewski A Tags: Chemistry Source Type: research