Dynamics of Energy Transfer in a Conjugated Dendrimer Driven by Ultrafast Localization of Excitations

Abstract

Solar energy conversion starts with the harvest of light, and its efficacy depends on the spatial transfer of the light energy to where it can be transduced into other forms of energy. Harnessing solar power as a clean energy source requires the continuous development of new synthetic materials that can harvest photon energy and transport it without significant losses. With chemically-controlled branched architectures, dendrimers are ideally suited for these initial steps, since they consist of arrays of chromophores with relative positioning and orientations to create energy gradients and to spatially focus excitation energies. The spatial localization of the energy delimits its efficacy and has been a point of intense research for synthetic light harvesters. We present the results of a combined theoretical experimental study elucidating ultrafast, unidirectional, electronic energy transfer on a complex molecule designed to spatially focus the initial excitation onto an energy sink. The study explores the complex interplay between atomic motions, excited-state populations, and localization/delocalization of excitations. Our findings show that the electronic energy-transfer mechanism involves the ultrafast collapse of the photoexcited wave function due to nonadiabatic electronic transitions. The localization of the wave function is driven by the efficient coupling to high-frequency vibrational modes leading to ultrafast excited-state dynamics and unidirectional efficient energy funneling. This work provides a long-awaited consistent experiment-theoretical description of excited-state dynamics in organic conjugated dendrimers with atomistic resolution, a phenomenon expected to universally appear in a variety of synthetic conjugated materials.

Is energy transfer limiting multiphotochromism? answers from ab initio quantifications

“…42 For instance in π-extended supramolecules with intramolecular energy transfer, 46 such effects have to be accounted for to reach an accurate reproduction of the experimental photophysics. If excited-state quantum dynamics can ultimately describe the migration of an excitation within the D/A system along time, 48 some of us also showed that a less cumbersome "static" TD-DFT model allows bypassing the above-listed limitations of standard models thanks to the calculation of the electronic coupling between the excited-states of molecules. If excited-state quantum dynamics can ultimately describe the migration of an excitation within the D/A system along time, 48 some of us also showed that a less cumbersome "static" TD-DFT model allows bypassing the above-listed limitations of standard models thanks to the calculation of the electronic coupling between the excited-states of molecules.…”

An ab initio multiple cloning approach for the simulation of photoinduced dynamics in conjugated molecules

“…9 An adequate theoretical treatment of such processes can be achieved by using direct or on-the-fly non-adiabatic molecular dynamics methods. [10][11][12] A sub-family of these approaches, based on trajectory surface hopping (SH) algorithms, [13][14][15][16] have been extensively used to study the photophysics and photochemistry of a wide variety of organic molecules: dendrimers, [17][18][19][20] nanohoops, [21][22][23] fluorenes, 24 fullerenes, 25 Ru(II)-based complexes, 26 chlorophylls, [27][28][29] retinal, 30 nucleotides [31][32][33][34][35][36][37] and so on. Different SH computational implementations are represented by NEWTON-X, 38,39 SHARC (Surface Hopping including ARbitrary Couplings), 40 PYXAID (PYthon eXtension for Ab Initio Dynamics) 41,42 and NEXMD (Non-adiabatic EXcited-states Molecular Dynamics), 12,43 among others.…”

Light‐Harvesting Nanotubes Formed by Supramolecular Assembly of Aromatic Oligophosphates

“…[1][2][3][4][5][6][7][8][9][10][11] In light-harvesting systems,e nergy is absorbed by numerous chromophores and transferred to an acceptor. Polymers [12][13][14][15][16][17][18][19] and dendrimers [20][21][22][23][24][25][26] were used to arrange multiple organic chromophores around acceptor molecules.E fficient transport of the excitation energy is ak ey aspect for the construction of effective light-harvesting systems. [27] Thed egree of structural order determines the level of electronic coupling and, thus,t he efficiency of energy transfer in chromophore arrays.…”