Energy Releasing and Conformational Dynamics of Stilbene Dendrimers upon Photoisomerization

Abstract

The energy-releasing process and the conformational dynamics of stilbene dendrimers (tetramethoxystilbene (generation (G) 0, G1, G2, and G4) upon photoexcitation are studied by the time-resolved transient grating method. For all dendrimers, the excited triplet (T1) state formation was observed. From the time-resolved studies on energy and the molecular volumes changes, it is found that the conformational change completes with the decay of the T1 state for G0−G2. However, the dynamics is slightly slower for G4, which is attributed to the conformational change of the dendron part. The molecular volume change due to the conformational rearrangement of the dendron upon the trans to cis isomerization is slightly positive (molecular expansion). The expansion is explained in terms of the creation of the void volume surrounded by the dendron side chains. Although the diffusion coefficient (D) of the trans and cis forms of G0 is almost the same, the difference becomes larger with increasing generation. This is clear evidence for the large conformational change upon isomerization. The larger D of the trans form compared with that of the cis form is explained in terms of the surface roughness of the dendrimers.

A new approach exploiting thermally activated delayed fluorescence molecules to optimize solar thermal energy storage

“…In addition, the changes in the TADF decay dynamics were negligible before, during, and after, e.g., 3 days of irradiation (see Supplementary Figs. 17,20). The results are indicative of the retardation of triple-triplet energy transfer and hence a lack of NBD → QC isomerization.…”

“…Energy storage can also be accomplished through photoisomerization 8 . A considerable number of molecular solar thermal (MOST) systems incorporating organic compounds, including anthracene 9,10 , azobenzene [11][12][13] , dihydroazulene 14,15 , norbornadiene-quadricyclane [16][17][18] , stilbene 19,20 , and ruthenium fulvalene derivatives 21,22 , which can undergo light-induced isomerization to metastable isomers for storage of solar energy, have been proposed.…”

Stilbene Photoisomerization

“…Clear evidence for the large conformational change upon isomerization of stilbene (tetramethoxystilbene) dendrimers of generation G0, G1, G2, and G4 was presented [105]. From the time-resolved studies on energy and molecular volumes changes, it was found that the conformational change upon the trans-to cis-isomerization completed with the decay of the T 1 state for G0-G2.…”

Stilbene-cored poly(glutamate) dendrimers

“…In this area, the photoisomerization of dendrimers with photoresponsive cores-such as stilbene, [13][14][15][16][17][18][19][20][21] azobenzene, [22][23][24][25][26][27][28][29][30][31][32][33] diarylethene, [34][35][36][37][38] intramolecularly hydrogen-bonded chromophores, [39][40][41] and photolabile chromophores 42-44 -has been extensively investigated. We recently reported that stilbene dendrimers with benzyl ether-type dendrons exhibited a volume-conserving isomerization mechanism and a macromolecular effect (or generation effect) on energy transfer efficiency from the peripheral dendrons to the core stilbene in organic solvents [45][46][47] and aqueous solution. [48][49][50] In these cases, the core stilbene unit played an important role as a photo-trigger for large conformational changes (photoisomerization), and as a fluorescent probe for detecting the environment inside the dendrimer.…”