Optical Excitations in Star-Shaped Fluorene Molecules

Montgomery, Neil A.; Denis, Jean-Christophe; Schumacher, Stefan; Ruseckas, Arvydas; Skabara, Peter J.; Kanibolotsky, Alexander L.; Paterson, Martin J.; Galbraith, I.; Turnbull, Graham A.; Samuel, Ifor D. W.

doi:10.1021/jp1109042

Cited by 41 publications

(61 citation statements)

References 35 publications

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“…Photoluminescence spectra of these materials exhibit three vibronic features (0-0, 0-1 and 0-2 transitions) characteristic to these oligofluorenes. 10 In solution, the peak absorbance for T3, T4 and T6 are found at 370, 375 and 379 nm, respectively. As the length of the fluorene arm is increased, both photoluminescence and absorbance features slightly red-shift.…”

Section: Resultsmentioning

confidence: 98%

“…Previously, the linear absorption cross-section of the star-shaped oligofluorenes with increasing arm lengths were shown to exhibit up to 3-fold enhancement as compared to their linear oligomer counterparts owing to the branching of the molecular structure. 10 Here, we investigated the nonlinear optical absorption crosssection via the open aperture z-scan technique. 40 The transmittance of a Gaussian laser beam (800 nm, 120 fs, 1 kHz repetition rate and 3.8 mJ per pulse energy) was measured through a 1 mm Scheme 1 Synthetic procedure for the T6 compound.…”

Section: Resultsmentioning

confidence: 99%

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Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

et al. 2015

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ae Nonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm À2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm À2 , which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

et al. 2015

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“…In our experiments, the ultrafast molecular dynamics following excitation is analyzed based on time-resolved fluorescence depolarization, a powerful tool to understand relaxation processes in molecular systems. 16,17 To gain true microscopic insight into dynamics and in particular EET, nonadiabatic molecular dynamics based on trajectory surface hopping can be employed. 18 For large sized systems such dynamics require semiempirical methods like OM2/MRCI and DFTB for the quantum chemical calculations 19,20 that are combined with the classical propagation of the nuclei in the excited states including nonadiabatic couplings allowing switches between different electronic states.…”

Section: -13mentioning

confidence: 99%

Ultrafast Electronic Energy Transfer in an Orthogonal Molecular Dyad

Wiebeler

Plasser

Hedley

et al. 2017

J. Phys. Chem. Lett.

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Understanding electronic energy transfer (EET) is an important ingredient in the development of artificial photosynthetic systems and photovoltaic technologies. Although EET is at the heart of these applications and crucially influences their light-harvesting efficiency, the nature of EET over short distances for covalently bound donor and acceptor units is often not well understood. Here we investigate EET in an orthogonal molecular dyad (BODT4), in which simple models fail to explain the very origin of EET. On the basis of nonadiabatic ab initio molecular dynamics calculations and ultrafast fluorescence experiments, we gain detailed microscopic insights into the ultrafast electrovibrational dynamics following photoexcitation. Our analysis offers molecular-level insights into these processes and reveals that it takes place on time scales ≲100 fs and occurs through an intermediate charge-transfer state.

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“…The conjugative coupling has not been improved and the torsion of the molecular skeleton would hamper electronic couplings. The molecular geometry validly affects the electronic density distribution, which was calculated by eliminating the C 6 H 13 side chains, 36 presented in Fig. 5(b).…”

Section: Theoretical Molecular Geometries and Electronic Transitionsmentioning

confidence: 99%

The molecular picture of amplified spontaneous emission of star-shaped functionalized-truxene derivatives

Zhou

et al. 2015

J. Mater. Chem. C

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Organic optical gain materials are the basis for organic solid-state lasers. However, the fundamental mechanism for Amplified Spontaneous Emission (ASE) is absent. Herein, three star-shaped molecules based on a truxene core with p-conjugated arms are studied to illuminate the influence of the molecular structure on ASE performance. We found that the three compounds demonstrated different ASE characteristics. The strong conjugated linkage in the molecular arms enhanced ASE, while the attenuated conjugated linkage deteriorates ASE for the given molecular structures. Based on the theoretical analysis, the conjugative coupling suppresses the low-frequency vibration, which is beneficial to the formation of an effective ''four-level'' energy system for ASE. On the contrary, the poor conjugative coupling brings out a mass of low-frequency modes, and hence, continuous vibronic energy sublevels will ruin the molecular ''four-level'' energy system. Our study presented a clear picture to clarify the ASE mechanism and offers valuable guidance for the design of new organic optical gain materials.

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Optical Excitations in Star-Shaped Fluorene Molecules

Cited by 41 publications

References 35 publications

Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

Ultrafast Electronic Energy Transfer in an Orthogonal Molecular Dyad

The molecular picture of amplified spontaneous emission of star-shaped functionalized-truxene derivatives

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