Ultrafast Energy Transfer in a Regioregular Silylene-Spaced Copolymer

Abstract

The energy-transfer properties of a regioregular silylene-spaced alternating donor−acceptor copolymer (donor−SiMe2−acceptor−SiMe2) m are determined with time-resolved spectroscopy; 4,4′-divinylbiphenyl serves as donor and 4,4′-divinylstilbene as acceptor. Steady-state fluorescence spectra show that the energy transfer is efficient. With excitation at 266 nm, fluorescence up-conversion curves at various detection wavelengths are measured to explore the detailed dynamics of the energy transfer. A rate ∼(0.3 ps)−1 for energy transfer between the S1 states of the donor and acceptor moieties is observed. Theoretical calculations based on fragment excitation difference provide a rate of energy transfer near the experimental value with detailed insight into the mechanism of energy transfer. The results of theoretical calculations indicate that the Coulomb interaction is dominant and the Dexter process is weak. The high-multipole interactions are important for energy transfer.

Photoinduced Ultrafast Intramolecular Excited-State Energy Transfer in the Silylene-Bridged Biphenyl and Stilbene (SBS) System: A Nonadiabatic Dynamics Point of View

“…20 A similar conclusion is also reached with our MD-OPT sampling process. More details concerning the sampled geometries with the MD-OPT method are given in Table S1- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 16 (the a-C3-n isomer defined in Table S2, Supporting Information, the so-called cis-anti-anti configuration in Hsu's work [19][20] as the reference example to explain the basic features of the ground and excited states of the SBS system. A similar ground-state minimum of this reference configuration was obtained at both the B3LYP/def2-SVP and BH&HLYP/def2-SVP levels, implying the weak dependence of the ground-state feature on the functional.…”

“…In addition, the different orientations of the two vinyl groups (VJ1 and VJ2) with respect to the -SiH 2 group also define different conformations; see examples in Scheme 3. The detailed definition of these conformations was discussed in previous works [19][20] and in Table S1, Supporting Information. Furthermore, as noted by Hsu and co-workers, many 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 isomers of the SBS system have similar energies (<6 kJ/mol).…”

“…Furthermore, as noted by Hsu and co-workers, many 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 isomers of the SBS system have similar energies (<6 kJ/mol). 20 In this sense, the determination of the initial conditions for nonadiabatic dynamics is quite challenging because it is not easy to take both multiple minima and their associated velocities into account. In practice, we employed two different initial sampling methods in this work.…”

“…In this approach, we only considered one stable configuration (the a-C3-n isomer defined in Table S2, Supporting Information, the so-called cis-anti-anti configuration in Hsu's work [19][20] as the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 reference geometry. Then, the initial conditions (geometries and velocities) were generated from the Wigner distribution function of the normal modes of the reference geometry.…”

“…3,[6][7][8][9][10][11][12][13][14][15][16][17] As one of the essential photo-physical processes, the intramolecular EET processes among different conjugated units in Si-linked oligothiophenes or polymers were widely studied in recent years. 1,11,[18][19][20] In a series of joint experimental-theoretical works by Chen, Hsu, and their co-workers, a few silylene-spaced co-polymers such as [(DA) m and (D 3 A) m ], [19][20] which are composed of electron donor D units (biphenyl), electron acceptor A units (stilbene), and silylene bridges, were studied. In their timeresolved experiments, both co-polymers show similar ultrafast intramolecular D-A EET (~300 fs) processes.…”