Ultrafast Energy Transfer Dynamics in a Squaraine Heterotriad

Abstract

A squaraine heterotriad consisting of three different covalently linked squaraine chromophores was synthesized, and its absorption spectra were interpreted in terms of Kasha's exciton coupling theory. Using the exciton couplings derived from model dyads (ca. 700 cm −1 ) as the input, we were able to predict the exciton state energies of the heterotriad. Transient absorption spectroscopy with femtosecond time resolution showed that excitation of the highest exciton state populates a state mainly localized at one terminal squaraine chromophore, and energy transfer to the lowest exciton state localized at the other terminal squaraine occurs within 30 fs. Field-induced surface hopping dynamics simulations support the assumption of ultrafast energy transfer. Moreover, they show the close relationship between internal conversion and energy transfer in the intermediate to weak coupling regime. The latter is a consequence of excitation localization caused by molecular vibrations.

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing

“…21 Covalently connected LH systems based on two step energy transfer, panchromatic absorption and large Stokes shi are suitable for multiple sensing and imaging applications. 22 Reports on two step cascade energy transfer based multichromophoric RGB LH systems are achieved mostly through dendritic design [23][24][25][26][27] such as dendritic solar concentrators, 28 arrays, 13,[29][30][31] small molecule based funnels, 9,32,33 heterotriads 34 and templated chromophore assemblies on peptide scaffolds, 35 DNA scaffolds 36 and organic nanostructures. 37 FRET based LH systems have also been utilized in organic photovoltaics, 38 photocatalysis, 39 photodynamic therapy, 40 bioimaging, 41 ratiometric temperature sensing and ion sensing 21,[42][43][44] in recent years.…”

Surface hopping modeling of charge and energy transfer in active environments

“…This approach was later used to investigate ultrafast energy transfer in squaraine heterotriad. 239 Sangiogo Gil et al recently presented an excitonic model which combines the Frenkel exciton model, surface hopping, and FOMO-CI to investigate the electronic energy transfer in multichromophoric systems. 98 In this model, the energies and couplings between the chromophores are evaluated using FOMO-CI.…”

Surface hopping modeling of charge and energy transfer in complex environments

“…This approach was later used to investigate ultrafast energy transfer in squaraine heterotriad. 226 Sangiogo Gil et al recently presented an excitonic model which combines the Frenkel exciton model, surface hopping, and FOMO-CI to investigate the electronic energy transfer in multichromophoric systems. 218 In this model, the energies and couplings between the chromophores are evaluated using FOMO-CI.…”