Modeling the Nonradiative Decay Rate of Electronically Excited Thioflavin T

Abstract

A computational model of nonradiative decay is developed and applied to explain the time-dependent emission spectrum of thioflavin T (ThT). The computational model is based on a previous model developed by Glasbeek and co-workers (van der Meer, M. J.; Zhang, H.; Glasbeek, M. J. Chem. Phys. 2000, 112, 2878) for auramine O, a molecule that, like ThT, exhibits a high nonradiative rate. The nonradiative rates of both auramine O and ThT are inversely proportional to the solvent viscosity. The Glasbeek model assumes that the excited state consists of an adiabatic potential surface constructed by adiabatic coupling of emissive and dark states. For ThT, the twist angle between the benzothiazole and the aniline is responsible for the extensive mixing of the two excited states. At a twist angle of 90°, the S(1) state assumes a charge-transfer-state character with very small oscillator strength, which causes the emission intensity to be very small as well. In the ground state, the twist angle of ThT is rather small. The photoexcitation leads first to a strongly emissive state (small twist angle). As time progresses, the twist angle increases and the oscillator strength decreases. The fit of the experimental results by the model calculations is good for times longer than 3 ps. When a two-coordinate model is invoked or a solvation spectral-shift component is added, the fit to the experimental results is good at all times.

Effect of acidic and basic pH on Thioflavin T absorbance and fluorescence

“…In the amyloid-bound state, the internal rotation of the ThT molecular segments is inhibited, therefore the electron cannot cross from LE into the non-radiative "dark" CT state. As the LE state has high oscillator strength, suppression of the LE → TICT quenching enhances radiative locally excited-state relaxation to the ground state resulting in strong increase in ThT fluorescence signal (Amdursky et al 2012;Erez et al 2011).…”

Ultrafast Twisting Dynamics of Thioflavin‐T: Spectroscopy of the Twisted Intramolecular Charge‐Transfer State

“…[24,25] Huppert and co-workers extensively studied the viscosity, temperature, and pressure dependence of the fluorescence yields and lifetimes of ThT and the nonradiative process of ThT was discussed in the context of several known nonradiative models. [26][27][28][29] Comparative fluorescence studies with structurally tailored derivatives of ThT unequivocally established the fact that twisting of the central bond that connected the benzothiazole moiety and the dimethylaniline group was responsible for efficient nonradiative relaxation. [30] Recently, the simulation of photoelectron spectra of ThT by Ren et al revealed that torsional relaxation around the central bond took place in about 300 fs.…”

Wagging motion of hydrogen-bonded wire in the excited-state multiple proton transfer process of 7-hydroxyquinoline·(NH3)3 cluster

“…Proton transfer is one of the most important reactions in acidbase chemical and biological dynamics caused by the site-specific interaction such as hydrogen bonding [24][25][26][27][28][29]. The skeletal mechanistic picture proposed by Grotthuss is still a guide for our understanding of the proton hopping in hydrogen-bonded systems [30,31].…”