Ultrafast Excited-State Proton Transfer of 2-(2‘-Hydroxyphenyl)benzothiazole: Theoretical Analysis of the Skeletal Deformations and the Active Vibrational Modes

Abstract

The involvement of skeletal deformations in the ultrafast excited-state proton transfer of 2-(2‘-hydroxyphenyl)benzothiazole (HBT) and the identification of the vibrational modes active in the process are reported. A multidimensional ab initio calculation of ground and excited states at the HF/DFT and CIS/TDDFT level renders the relevant portions of the potential energy surfaces around the minimum-energy path connecting the enol and keto configuration. The frequencies and potential energy distributions of the normal modes and the corresponding deformations of the molecule are calculated for all minimum-energy geometries. Along the minimum-energy path, the nuclear deformation is projected onto the relevant normal modes. This normal-mode analysis shows that mainly five low-frequency in-plane vibrations are associated with the electronic rearrangement and the transfer of the proton. The theoretical findings are in quantitative agreement with the experimental study presented in the accompanying paper.

The excited‐state geometry of 1‐hydroxy‐2‐ acetonaphthone: a resonance Raman and quantum chemical study

“…Comparing the theoretical results obtained for HAN with recent CIS calculations reported by de Vivie-Riedle et al 42 for another ESIPT system, an almost identical pattern for the initial structural changes can be concluded. The enol excitedstate geometry of 2-(2 0 -Hydroxyphenyl)benzothiazole also shows large bond length changes for the chelate-ring bonds.…”

Femtochemistry of Guest Molecules Hosted in Colloidal Zeolites

“…Moreover, the conversion from the keto to the enol form is associated with a strong electronic reorganization of the electronic cloud that can be easily followed by absorption measurements. [17,30] The UV-vis absorption spectra of HBT dissolved in ethanolic solution and enclosed in the zeolite nanohosts are depicted in Figure 3. From previous studies it is known that the maximum of the first absorption band of enol-HBT is located at 335 nm and the first band of keto-HBT at 380 nm.…”

Direct Observation of Nuclear Motion during Ultrafast Intramolecular Proton Transfer

“…Ab initio calculations of electronically excited states in molecules exhibiting reactive dynamics are very challenging. High level PESs for the complete ESIPT pathway from the Franck-Condon point to the keto minimum are up to now only available for HBT [7] and very few other compounds [42,43]. It turns out that the frequencies of the skeletal modes vary only little from the electronically excited to the ground state.…”

“…The acceptor is typically a nitrogen or a second oxygen atom. Associated with the transfer is a shift of double bonds in the ring and a variation of the aro- maticity of the neighboring groups [7]. The ESIPT leads to a strong and characteristic Stokes shift between the UV absorption of the original enol-form and the visible fluorescence (see Fig.…”