Excitation Dynamics in Hetero‐bichromophoric Calixarene Systems

Abstract

In this work, the dynamics of electronic energy transfer (EET) in bichromophoric donor-acceptor systems, obtained by functionalizing a calix[4]arene scaffold with two dyes, was experimentally and theoretically characterized. The investigated compounds are highly versatile, due to the possibility of linking the dye molecules to the cone or partial cone structure of the calix[4]arene, which directs the two active units to the same or opposite side of the scaffold, respectively. The dynamics and efficiency of the EET process between the donor and acceptor units was investigated and discussed through a combined experimental and theoretical approach, involving ultrafast pump-probe spectroscopy and density functional theory based characterization of the energetic and spectroscopic properties of the system. Our results suggest that the external medium strongly determines the particular conformation adopted by the bichromophores, with a direct effect on the extent of excitonic coupling between the dyes and hence on the dynamics of the EET process itself.

Simulating vertical excitation energies of solvated dyes: From continuum to polarizable discrete modeling

“…Many benchmarks studies have been presented elaborating on the merits and limitations of TD‐DFT for the simulation of UV‐Vis spectroscopy, as well as on the most appropriate choice of functional and basis set combination for different types of system . And though many computational studies are carried out on isolated systems, solvent effects should not be neglected for the presence of the solvation environment can significantly alter the electronic absorption properties of a system, both qualitatively and quantitatively . For this reason, theoretical models have been developed to tackle this problem and then combined with DFT and TD‐DFT to include solvent effects within the theoretical model.…”

Understanding Förster Energy Transfer through the Lens of Molecular Dynamics

“…The comparison with the experiment is very good and indeed solves a theoretical problem associated with this system, where estimates of V DA from TD-DFT calculations on few preselected representative configurations of the D-clx-A system, underestimated the RET lifetimes by several orders of magnitude. 31 Our approach combines equilibrium and non-equilibrium MD calculations with TD-DFT results, leading to a detailed description of the concurrent processes: D * decay, energy transfer and conformational dynamics. The conformational motion modulates V DA , the intermolecular interaction responsible for RET.…”

“…Attempts to relate the different timescales to V DA obtained via TD-DFT for different configurations of the system were unsuccessful, with theoretically estimated timescales ranging from a few tenths to a few hundreds fs. 31 Here, while adopting the same approach to the V DA estimate, we are able to properly simulate RET timescales thanks to our fully dynamical approach to RET. We will demonstrate that the RET process is governed by a complex interplay between different competing dynamical processes that include not just the D radiative and non-radiative relaxation, but also the conformational and solvation degrees of freedom of the system that, modulating V DA on similar timescales as RET, cannot be neglected in the description of this dynamical phenomenon.…”

Time Programmable Locking/Unlocking of the Calix[4]arene Scaffold by Means of Chemical Fuels

“…[8,9,10] The consequences of this flexibility can be relevant on the calixarenep roperties, such as the availability of the aromatic cavity for guest complexation, [10] the macrocycle self-assembly properties [11] or the spectroscopic properties of calixarene-based dyes. [12,13] To the best of our knowledge,c ontrol on the conformational equilibrium of Figure 1h as been mainly attainedt hrough ac hange of the solvent, [10,12,14,15] at ime-consuming operation that does not allow for af ast switch between the two pinched cone structures. We figured that the use of ac hemical fuel to inducet he conformational change of the calixarene scaffold would be highly desirable as ac onvenient way to favor one of the two pinched cone structuresi natime-controlled and programmable fashionwithout recurring to avariation of the solvent.…”

“…When the calixarene is functionalized also at the upper rim, this equilibrium can be shifted towards one of the two possible pinched structures as a result of attractive or repulsive interactions between the upper rim distal substituents [8, 9, 10] . The consequences of this flexibility can be relevant on the calixarene properties, such as the availability of the aromatic cavity for guest complexation, [10] the macrocycle self‐assembly properties [11] or the spectroscopic properties of calixarene‐based dyes [12, 13] . To the best of our knowledge, control on the conformational equilibrium of Figure 1 has been mainly attained through a change of the solvent, [10, 12, 14, 15] a time‐consuming operation that does not allow for a fast switch between the two pinched cone structures.…”