Excited-State Dynamics of [(1,1′-Biphenyl)-4,4-diyldi-2,1-ethenediyl]bis(dimethylsilane)

Abstract

The relaxation dynamics of excited electronic states of [(1,1'-biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(dimethylsilane) dissolved in various solvents with varied polarity and viscosity have been investigated. Upon excitation at wavelength 266 nm, we measured the fluorescence curves that exhibit a rise time constant approximately 100 fs, and two decay time constants, 7-65 ps and approximately 1 ns. We attribute the former decay to upper excited states to the S(1) state, and the latter decay to geometric relaxation and the lifetime of the S(1) state. Only the tens of picosecond decay shows a dependence on the solvent viscosity, indicating that the torsional motion dominates the relaxation. Theoretical calculations were performed to obtain the optimized structures of the free [(1,1'-biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(dimethylsilane) molecule in its ground and first excited states with methods B3LYP/6-311G(d) and CIS/6-311G(d), respectively. The results of these calculations show that the dihedral angle between the two phenyl rings is approximately 34 degrees for trans and approximately 38 degrees for cis conformers in the ground state and that the first excited state has a planar structure, in agreement with the experimental results that indicate that the torsional motion of two phenyl groups elevates the relaxation of the S(1) state. Enhanced vibrational relaxation of S(1) in alcoholic solvents is observed. Rapid relaxation in methanol-OH compared with that in methanol-OD is explained by the excess energy dissipated efficiently through high-frequency vibrational mode (>500 cm(-1)).

Determinants of the efficiency of photon upconversion by triplet–triplet annihilation in the solid state: zinc porphyrin derivatives in PVA

“…Figure 3 shows a typical data set (16.6 mW for G1 and 2.1 mW for G2 in this case), from which it is evident that ZnTMP and ZnDBP are the best upconverters in groups G1 and G2, respectively. As is well-known from photochemical studies, [42][43][44] both the pattern of macrocycle substitution by the phenyl groups and the substitution of the phenyl moieties themselves with alkyl groups that act as impediments to free torsional motion can have substantial effects on the efficiencies of UC in these dual absorber-upconverter systems. We defer discussion of these differences until the calculations of the dimer potential surfaces have been presented.…”

Controlling Conformations in Alternating Dialkylsilylene‐Spaced Donor–Acceptor Copolymers by a Cooperative Thorpe–Ingold Effect and Polymer Folding

“…Monosilylene-spaced copolymers 1 [14] are known to exhibit extraordinary photophysical properties; [15][16][17][18] furthermore, different aryl groups (i.e., Ar 1 and Ar 2 ) can be regioselectively incorporated in the polymer chain by using a simple hydrosilylation protocol. The silicon moiety in 1, in general, Abstract: A series of dialkylsilylenespaced copolymers 6 and 7, which contain Me 2 Si and iPr 2 Si spacer groups, respectively, and have alternating donor and acceptor chromophores, have been designed and regioselectively synthesized by hydrosilylation.…”

C–N Bond Rotation Controls Photoinduced Electron Transfer in an Aminostyrene–Stilbene Donor–Acceptor System

“…Vibrational analysis for the optimized geometries in the GS was carried out to ensure the stability of the optimized structures. B3LYP exchange–correlation functional was successfully adopted by Hsu and co-workers to calculate equilibrium geometry and excited-state properties of silylene-spaced divinylbiphenyl–divinylstilbene dimers, which are similar to our system, , so we are convinced that this level of theory is reliable. Dispersion interaction between aminostyrene moiety and stilbene moiety may play an important role in excited-state properties and relative energy of conformers; hence, Grimme’s D3 correlations were used in our calculations .…”

“…On the other hand, complex polymer folding behavior and strongly solvent-dependent photoinduced electron transfer dynamics have also been observed in these silylene-spaced copolymer systems, making the full elucidation of their photophysical behaviors extremely nontrivial. 6,[8][9][10][11]15,16 Among the synthetic silylene-spaced copolymer systems, the dimethylsilylene-spaced aminostyrene−stilbene copolymers (Scheme 1) might be the one group with unusual photophysical properties that are the most challenging to fully understand. Photoinduced electron transfer from aminostyrene to stilbene has been observed in oligomers and copolymers; therefore, the aminostyrene−stilbene pair is designated as a donor−acceptor (DA) dimer with aminostyrene as the electron donor and stilbene as the acceptor.…”

“…Functional organic materials incorporating both donor and acceptor chromophores in the molecular backbone are fundamental in light emitting, light harvesting, artificial photosynthesis, and sensing applications. , In particular, various linear polymers with alternating donor and acceptor moieties connected by silylene spacers have recently drawn considerable research attention because of their applications in light-harvesting materials, − electron transfer materials, , and polymer foldamers. − In these alternating copolymer systems, the silylene bridge acts as an insulating spacer that prevents electronic delocalization between neighboring chromophores, while still allowing efficient through-space energy transfer or charge transfer between the chromophores to occur. − This design hence enables a great deal of tunability in the photophysical properties of the materials by controlling the chemical compositions of the individual donor and acceptor segments. On the other hand, complex polymer folding behavior and strongly solvent-dependent photoinduced electron transfer dynamics have also been observed in these silylene-spaced copolymer systems, making the full elucidation of their photophysical behaviors extremely nontrivial. ,− ,, …”