Ultrafast polarized fluorescence dynamics in an organic dendrimer

Varnavski, Oleg; Menkir, Getahun; Burn, Paul L.

doi:10.1063/1.1289495

Cited by 32 publications

(39 citation statements)

References 19 publications

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“…Generally, a fast fluorescence depolarization could be an indication of the energy migration between differently oriented chromophores. [20][21][22][23] Shown in Fig. 5 is the result of ultrafast upconversion measurements of the fluorescence anisotropy in a CZD4SNC2 dendrimer at 630 nm.…”

Section: Shown Inmentioning

confidence: 99%

Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

et al. 2000

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The ultrafast intrinsic dynamics of an organic dendrimer in solution and in a thin film is reported using fluorescence upconversion spectroscopy. Femtosecond decay is detected at higher emission energies, while at lower energies a fluorescence rise time (ϳ3 ps͒ was observed that is dependent on the solvent's polarity. A strong excitation energy dependence of the decay pattern was also observed. Different synthetic functional groups that comprise the macromolecular dendrimer structure were investigated. The mechanism, which describes the complex dynamics in the dendrimer system, was found to be associated with the excitation of the attached chromophore nitroaminostilbene. These results indicate the absence of excited-state interactions of functional groups within the dendrimer macromolecule. A model, which includes the existence of an intermediate nonradiative state, is proposed to describe the complex ultrafast fluorescence dynamics in the dendrimer system.

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Section: Shown Inmentioning

confidence: 99%

Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

et al. 2000

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“…The decay is much faster for G0 at 290 K, but identical for both generations at 4 K. For comparison, solutions of the G0 dendrimer were also investigated. Apart from a broadening and redshift on the scale of a few ps, 21 no change in the emission spectrum was detected up to 4 ns after excitation. Figure 3 shows the time dependence of the blue edge of the emission spectra ͑defined as 10% of the peak intensity͒ for G0 and G3 at 290 and 4 K. For G0 the shift occurs within 40 ps at both temperatures, whereas for G3 the relaxation …”

Section: Resultsmentioning

confidence: 98%

“…[21][22] At 4 K, the molecules are more planar, and excitation does not cause further planarization. This does not exclude the presence of an energetic distribution of conformers even at low temperatures, which then give rise to the spectral redshift.…”

Section: Discussionmentioning

confidence: 99%

“…21 Also, the rapid conformational relaxation and strong intermolecular delocalisation have been linked with an ultrafast depolarisation of the emission on a similar time-scale. 21,22 Excitation was also performed at 420 nm, which corresponds to the absorption of the dendrimer core, whereas both core and dendrons absorb at 370 nm. 16,22 No difference in the decay dynamics were observed, however.…”

Section: Figmentioning

confidence: 99%

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Origin of spectral broadening in π-conjugated amorphous semiconductors

2002

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We present a study of the picosecond fluorescence dynamics of -conjugated semiconducting organic dendrimers in the solid state. By varying the degree of branching within the dendrons, referred to as the dendrimer generation, a control of intermolecular spacing of the emissive core and therefore of the lattice parameter for Förster-type energy transfer is achieved. This allows a distinction between spectral diffusion and excimer formation as the two main sources of spectral broadening in organic semiconductors. Whereas Förster-type dispersive spectral relaxation is independent of temperature but strongly dependent on the interchromophore distance, excimer formation is also strongly thermally activated due to temperature-dependent conformational changes and the influence of thermally activated dynamic disorder. The rapid spectral diffusion allows a determination of the excimer rise in the emission, which is shown to have a profound impact on the steady state luminescence properties of dendrimer films. We show that the dendrimer generation not only allows a microscopic control of intermolecular interactions but also a direct control of the rate of spectral diffusion. Implications for the design of novel materials for optoelectronic devices are discussed.

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“…3,19−22 A number of experimental studies have been carried out to study the intramolecular EET between different subunits for branched molecules. 23 −25 In particular, the organic dendrimers with rotational symmetry (such as the existence of C 3 or C 4 rotational axes) have attracted considerable attention since the efficient EET is expected among those equivalent branches. With the development of laser technology, time-dependent fluorescence depolarization may provide useful information on the energy-transfer processes of such high-symmetric systems.…”

Section: ■ Introductionmentioning

confidence: 99%

Photoinduced Excited-State Energy-Transfer Dynamics of a Nitrogen-Cored Symmetric Dendrimer: From the Perspective of the Jahn–Teller Effect

Huang

Wang

et al. 2015

J. Phys. Chem. C

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We report an interesting view to understand the ultrafast excited-state energy-transfer (EET) process in the D 3 -symmetric dendrimer tris(4-ethynylphenyl)amine (TEPA) from the perspective of the well-known E⊗e Jahn−Teller (JT) effect. Upon excitation to two lowest excited states (S 1 and S 2 ) with doubly degenerate E symmetry, two sets of e vibrational modes, dihedral angle twist and strong pyramidalization near the nitrogen core, lead to the JT distortion and symmetry lowering. Through the excited-state dynamics simulation with the onthe-fly surface-hopping approach at the TDDFT level, we find that the system may either travel three equivalent minima of S 1 state or undergo the nonadiabatic transitions between S 1 and S 2 states. These motions induce the ultrafast EET among different branches and the reorientation of the transition dipole moments, finally leading to the ultrafast fluorescence anisotropy decay. This energy-transfer mechanism can provide some interesting insights on the excited-state dynamics of large dendrimers with three equivalent branches and transition metal complexes with C 3 symmetry. ■ INTRODUCTIONOrganic dendrimers show attractive photovoltaic properties such as efficient photoharvesting, 1,2 unidirectional energy transfer, 3 enhanced two-photon absorption, 4−6 and high photoluminescence quantum yield. 7,8 These properties make them potentially useful in photovoltaic materials for solar energy conversion, 1,3,9 fluorescence sensors, 10,11 organic lightemitting diodes, 12,13 and organic lasers. 8,14 The fundamental photophysics and photochemistry of these novel dendritic macromolecular architectures involve the exciton formation and movement (localization or delocalization), 15−18 especially the intramolecular excited-state energy transfer (EET) between different subunits (branches). 3,19−22 A number of experimental studies have been carried out to study the intramolecular EET between different subunits for branched molecules. 23−25 In particular, the organic dendrimers with rotational symmetry (such as the existence of C 3 or C 4 rotational axes) have attracted considerable attention since the efficient EET is expected among those equivalent branches. With the development of laser technology, time-dependent fluorescence depolarization may provide useful information on the energy-transfer processes of such high-symmetric systems. 25−29 This special technology allows us to monitor the orientation change of the emission dipole with respect to the absorption dipole, which is caused by the variation of local excitation with time. Goodson III and collaborators studied the intramolecular EET mechanism of several dendrimers, such as T-NPTPA, 25,29 A-DSB, 30,31 G n , 32 and so on. With timeresolved spectroscopy, they reported that a group of tribranched molecules with a nitrogen core show a very fast energy transfer among different branches on the ∼30−100 fs time scale. Through the investigation of a series of branched molecules with similar building blocks (chromophores) and different core un...

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Ultrafast polarized fluorescence dynamics in an organic dendrimer

Abstract: The dependence of the ultrafast relaxation kinetics of the S 2 and S 1 states in β -carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies

Cited by 32 publications

References 19 publications

Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

Origin of spectral broadening in π-conjugated amorphous semiconductors

Photoinduced Excited-State Energy-Transfer Dynamics of a Nitrogen-Cored Symmetric Dendrimer: From the Perspective of the Jahn–Teller Effect

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