Dielectric tensor of tetracene single crystals: The effect of anisotropy on polarized absorption and emission spectra

Tavazzi, Silvia; Raimondo, L; Silvestri, Leonardo; Spearman, P.; Camposeo, Andrea; Polo, M.; Pisignano, Dario

doi:10.1063/1.2897436

Cited by 58 publications

(110 citation statements)

References 43 publications

(58 reference statements)

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“…Consequently, the largest anisotropy in ERA is expected to be between the a and b axes, and a much smaller anisotropy is expected between the b and c axes. Indeed, the observed anisotropy in both absorption and emission between the a and b axes is B3-fold as measured by Tavazzi et al 33 In contrast, the largest p-orbital overlap anisotropy and hence the triplet exciton hopping anisotropy is between the b and c axes (Fig. 3b).…”

Section: Article Nature Communications | Doi: 101038/ncomms4646mentioning

confidence: 75%

Visualization of exciton transport in ordered and disordered molecular solids

et al. 2014

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Transport of nanoscale energy in the form of excitons is at the core of photosynthesis and the operation of a wide range of nanostructured optoelectronic devices such as solar cells, lightemitting diodes and excitonic transistors. Of particular importance is the relationship between exciton transport and nanoscale disorder, the defining characteristic of molecular and nanostructured materials. Here we report a spatial, temporal and spectral visualization of exciton transport in molecular crystals and disordered thin films. Using tetracene as an archetype molecular crystal, the imaging reveals that exciton transport occurs by random walk diffusion, with a transition to subdiffusion as excitons become trapped. By controlling the morphology of the thin film, we show that this transition to subdiffusive transport occurs at earlier times as disorder is increased. Our findings demonstrate that the mechanism of exciton transport depends strongly on the nanoscale morphology, which has wide implications for the design of excitonic materials and devices.

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Section: Article Nature Communications | Doi: 101038/ncomms4646mentioning

confidence: 75%

Visualization of exciton transport in ordered and disordered molecular solids

et al. 2014

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“…Below 3 eV, the TEN spectrum presents the typical spectral features coming from the well known anisotropic optical response of TEN single crystals when oriented as our substrate and analyzed by polarized light. 22 In the spectral range between 3 and 4 eV, where TEN is known to be transparent, a featureless background is detected. It originates from the interference due to the crystal finite thickness ͑as indeed checked by measuring different TEN samples, not shown here͒.…”

Section: Dipartimento DI Scienza Dei Materiali and Cnism Università mentioning

confidence: 99%

“…The crystal axes a TEN and b TEN on the TEN͑001͒ surface were previously identified from the known anisotropy of the TEN substrate by polarized optical microscopy ͑uncertainty of Ϯ2°͒, exploiting its birefringence and dichroism. 21,22 During the OMBE experiment, RAS spectra have been collected every 1.2Ϯ 0.1 nm nominal thickness of the deposited film, stopping the molecular flux during the optical measurements.In Fig. 1, we report the RAS spectrum collected in situ on the TEN crystal substrate and all the spectra collected in situ at different growth stages, up to 5 nm thickness of the film.…”

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confidence: 99%

Pseudomorphic growth of organic semiconductor thin films driven by incommensurate epitaxy

Sassella

Campione

Raimondo

et al. 2009

Applied Physics Letters

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A stable pseudomorphic phase of ␣-quaterthiophene, a well known organic semiconductor, is obtained by growing films with organic molecular beam epitaxy ͑OMBE͒ on a single crystal of another organic semiconductor, namely, tetracene. The structural characteristics of the new phase are investigated by monitoring in situ the OMBE process by reflectance anisotropy spectroscopy; thus assessing that incommensurate epitaxy is in this case, the driving force for tuning the molecular packing in organic molecular films and in turn, their solid state properties. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3081413͔The key factor improving the performances of thin film devices based on organic semiconductors is the achievement of high charge mobility through the control of growth mechanisms aimed at improving the structural quality and morphology of the thin films. 1 The fine tuning of the material properties by a suitable modification of the molecular orientation and packing ͑crucial for determining the electronic band structure of the solid film and its charge-transport properties͒ 2 represents an alternative experimental opportunity. The arrangement of different organic semiconductors in multilayer architectures, including semiconductor junctions, gives further beneficial effects in thin film devices. 1 In this framework, organic molecular beam epitaxy ͑OMBE͒ represents the best choice among the growth techniques, assuring high quality films and controlled interfaces in organic heterostructures in view of both fundamental studies and applications. 3,4 Among the strategies for growing samples with designed properties, one of the most promising is the use of organic substrates 5-7 whose effect in tuning the molecular orientation of the overlayer has been already demonstrated. In particular, when organic single crystals are used as substrates, highly oriented organic heterostructures are grown even in the absence of any geometric coincidence between substrate and overlayer ͑incommensurate epitaxy͒. 5,[8][9][10][11][12][13] In this letter, we investigate the properties of an organic-organic heterostructure by demonstrating the OMBE growth of an epitaxial pseudomorphic phase of the ␣-quaterthiophene ͑␣-4T͒ film on tetracene ͑TEN͒ single crystals. By means of reflectance anisotropy spectroscopy ͑RAS͒, we monitored in situ the OMBE process, showing that the ␣-4T overlayer grows with a distorted lattice structure with respect to the bulk crystal, which results in incommensurate epitaxy. In addition, the full ex situ stability of this new phase is demonstrated so that organic-organic epitaxy is definitely assessed as a powerful tool for tuning the properties of the growing films. 14 ␣-4T was synthesized and purified according to Ref. 15, while commercial TEN was purified by several sublimation steps before use. TEN single crystals were grown by physical vapor transport. 16 Its crystal structure belongs to the triclinic system, with unit cell parameters a = 6.06 Å, b = 7.84 Å, c = 13.01 Å, ␣ = 77.13°, ␤ = 72.12°, ␥ = 85.79...

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“…[46][47][48] Such structure results in anisotropic electronic and optical responses in tetracene crystals, manifested as anisotropic electronic diffusion 49 and polarized optical absorption/emission. 47,50 Since the transition dipoles are polarized, 47,50,51 the excitonic dynamics associated with the excited states should also be anisotropic as pointed out in similar materials. 52,53 However, this effect has rarely been considered in the available studies on SF dynamics.…”

Section: Introductionmentioning

confidence: 99%

Polarization-dependent exciton dynamics in tetracene single crystals

Zhang

et al. 2014

The Journal of Chemical Physics

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Abstract:We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.

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Dielectric tensor of tetracene single crystals: The effect of anisotropy on polarized absorption and emission spectra

Cited by 58 publications

References 43 publications

Visualization of exciton transport in ordered and disordered molecular solids

Visualization of exciton transport in ordered and disordered molecular solids

Pseudomorphic growth of organic semiconductor thin films driven by incommensurate epitaxy

Polarization-dependent exciton dynamics in tetracene single crystals

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