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Solvent effect on excited state potential energy surfaces of Thioflavin T. Qualitatively different results by TDDFT and SA‐2‐CASSCF methods
Author(s) -
Stsiapura Vitali I.
Publication year - 2020
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.26358
Subject(s) - time dependent density functional theory , excited state , chemistry , benzothiazole , conical intersection , thioflavin , solvation , intramolecular force , chromophore , photochemistry , fluorescence , solvent effects , density functional theory , computational chemistry , molecule , molecular physics , solvent , atomic physics , stereochemistry , organic chemistry , physics , pathology , medicine , disease , alzheimer's disease , quantum mechanics
Thioflavin T (ThT) is a viscosity‐sensitive fluorescent dye and its emission intensity undergoes a significant enhancement upon binding to DNA or amyloid fibrils. This fluorescence light‐up feature has been attributed earlier to restriction of structural rearrangements in the excited state that are coupled to an intramolecular charge transfer (ICT) reaction. In this work TDDFT (using B3LYP and CAM‐B3LYP functionals) and SA‐2‐CASSCF calculations were carried out to obtain relaxed excited‐state potential energy surfaces (PES) along twisting φ and wagging δ angles that describe mutual orientation of benzothiazole (BTZ) and dimethylaniline (DMA) fragments in ThT. For isolated ThT molecule both methods predict that during structural rearrangements of the initially excited Franck‐Condon state, besides twisting along CC bond which connects BTZ and DMA fragments, a considerable wagging motion is expected to occur. Account for solvent effect using polarized continuum model showed qualitative differences in the excited state PES features calculated by SA‐2‐CASSCF and TDDFT methods. Single‐reference TDDFT calculations failed to describe solvation of TICT state and predicted increase of its energy in more polar media.