Substrate‐Induced Phase of a Benzothiophene Derivative Detected by Mid‐Infrared and Lattice Phonon Raman Spectroscopy

Schrode, Benedikt; Jones, Andrew O. F.; Resel, Roland; Bedoya, Natalia; Schennach, Robert; Geerts, Yves; Ruzié, Christian; Sferrazza, Michele; Brillante, Aldo; Salzillo, Tommaso; Venuti, Elisabetta

doi:10.1002/cphc.201701378

Cited by 11 publications

(18 citation statements)

References 40 publications

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“…Thereby, phase differentiation can be achieved as the absorption peak corresponding to the aromatic quadrant stretching is located differently for the SIP phase, 1605 cm −1 , and for the Bulk phase, 1610 cm −1 . [31] The direct comparison of the PM-IRRAS spectra obtained for the our-prepared thin-films with those previously reported for the SIP and Bulk phases confirmed that, in all the cases, the SIP phase was formed and no traces of the Bulk phase were identified (Figure 2d).…”

Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 99%

“…A spectroscopic study by using mid-infrared and lattice phonon Raman microscopy has been previously reported to be a suitable approach for recognizing the Bulk and SIP phases of C 8 O-BTBT-OC 8 . [19,31] Therefore, the phase of all the freshly fabricated thin films © 2020 Wiley-VCH GmbH was characterized by polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Thereby, phase differentiation can be achieved as the absorption peak corresponding to the aromatic quadrant stretching is located differently for the SIP phase, 1605 cm −1 , and for the Bulk phase, 1610 cm −1 .…”

Section: Resultsmentioning

confidence: 99%

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Enhancing Long‐Term Device Stability Using Thin Film Blends of Small Molecule Semiconductors and Insulating Polymers to Trap Surface‐Induced Polymorphs

Salzillo

Campos

Babuji

et al. 2020

Adv Funct Materials

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The lack of long-term stability in thin films of organic semiconductors can often be caused by the low structural stability of metastable phases that are frequently formed upon deposition on a substrate surface. Here, thin films of 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene (C 8 O-BTBT-OC 8) and blends of this material with polystyrene by solution shearing are fabricated. Both types of films exhibit the metastable surface-induced herringbone phase (SIP) in all the tested coating conditions. The blended films reveal a higher device performance with a field-effect mobility close to 1 cm 2 V −1 s −1 , a threshold voltage close to 0 V, and an on/off current ratio above 10 7. In situ lattice phonon Raman microscopy is used to study the stability of the SIP polymorph. It is found that films based on only C 8 O-BTBT-OC 8 slowly evolve to the Bulk cofacial phase, significantly impacting device electrical performance. In contrast, the blended films stabilize the SIP phase, leading to devices that maintain a high performance over 1.5 years. This work demonstrates that blending small-molecule organic semiconductors with insulating binding polymers can trap metastable polymorphs, which can lead to devices with both improved performance and long-term stability.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Enhancing Long‐Term Device Stability Using Thin Film Blends of Small Molecule Semiconductors and Insulating Polymers to Trap Surface‐Induced Polymorphs

Salzillo

Campos

Babuji

et al. 2020

Adv Funct Materials

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“…MicroRaman spectroscopy in the lattice phonon region represents a very versatile technique currently employed to diagnose the presence of different structures grown in a variety of environments, such as films, nano-crystals or at solid interfaces [46][47][48]. The modes detected in the low energy region of the vibrational spectrum, i.e., the lattice phonons, owe their properties to the weak dispersion forces of the intermolecular field and are therefore distinctive of a given structure.…”

Section: Raman Characterization Of Single Crystalsmentioning

confidence: 99%

“…To summarize, the films obtained with the BAMS procedure showed the presence of well oriented α-phase only. Examples of surfaces stabilizing selectively a polymorphic modification are now numerous [47,48,[52][53][54][55][56], but less common is combination of selectivity and a high degree of iso-orientation.…”

Section: Thioindigo Film Characterizationmentioning

confidence: 99%

Crystal alignment of surface stabilized polymorph in thioindigo films

et al. 2020

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Thioindigo (2-(3-Oxo-1-benzothiophen-2(3H)-ylidene)-1-benzothiophen-3(2H)-one) is a synthetic dye related to the natural compound Indigo. Notwithstanding the interest aroused recently by its employment as a functional material in a number of applications, a satisfactory characterization of its solid state is still missing. In this work, we study the occurrence of the two thioindigo α and β polymorphs under various growth conditions, and find that their structural similarity implies they often coexist. However, whereas polymorph β is certainly predominant in the bulk phase, polymorph α grows preferentially on substrates, turning out to be the surface stabilized phase in highly homogeneous and ordered films obtained by the bar-assisted meniscus shearing method (BAMS). DFT calculations support the experimental findings, aiding in the polymorph spectroscopic identification and to the interpretation of the order in the films of polymorph α.

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A New Approach to Polymorphism in Molecular Crystals: Substrate‐Mediated Structures Revealed by Lattice Phonon Dynamics

Salzillo

Brillante

2022

Adv Materials Inter

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The experimental search for polymorph screening is often assisted by computational studies on crystal structure predictions. [8] Lastly, a subtle perspective of Bernstein cleared up a final revision of the terminology and of the nomenclature of multiple crystal forms. [9] In more recent years a new approach to polymorphism has taken momentum in the search of new crystal structures of organic materials, the so-called thin film structures or substrate-induced polymorphs (SIP), meaning a phase grown in the vicinity of a substrate with a distinct structure from those of the bulk. [10] An earlier discussion on the subject was held in a dedicated workshop about fifteen years ago. [11] At that time the discussion was mostly focused on organic semiconductors such as pentacene and perylene diimide derivatives. Since the majority of the thin film structures showed crystal parameters not very dissimilar from those of the corresponding parent bulk forms, these structures were indicated as "distortedbulk," where the term "distorted" was ascribed to the perturbation of the substrate on the molecular layers. Approximately ten years later, [12] a new grammar on substrate-induced structures was established. The growth at the interface of a variety of different substrates led to the definition of the general class of surface-mediated structures, portraying more detailed definitions such as "surface-induced" and "surface-selected" polymorphs, with the former indicating a bulk-distorted form and the latter being a new genuine structure with no association to any crystal phase of the bulk. This is the nomenclature that we shall initially follow in the present survey, with some new hints on additional cases that will be encountered, such as substratestabilized polymorphs, as detailed further on.Certainly, the starting point of surface-mediated polymorphs cannot be separated by the exhaustive review on SIP as discussed in Jones et al. [10] In that paper, examples of sixteen molecules were given, for which thin film polymorphs had been observed on solid substrates, showing new structures with respect to the previously known single crystals polymorphs. The impact of polymorphism on the material properties was mostly addressed on organic electronics, because every structure has its own mobility with relevant consequences on the efficiency of the device. Besides, it is wellThe issue of polymorphism in molecular crystals is discussed, taking into account the substrate-mediated structures, that is, structures grown at the interface of different substrates. Bulk and thin films of a compound both share the potentiality to display different crystal forms. However, unlike bulk polymorphs, whose structures are determined by their different molecular packing, thin film structures depend very much on the molecular organization of the organic layers on the substrate, which may, or may not, lead to an ordered structure, depending on the nature of the interface and on the growth conditions. Based on large part in some of the authors' recent works, the...

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Substrate‐Induced Phase of a Benzothiophene Derivative Detected by Mid‐Infrared and Lattice Phonon Raman Spectroscopy

Cited by 11 publications

References 40 publications

Enhancing Long‐Term Device Stability Using Thin Film Blends of Small Molecule Semiconductors and Insulating Polymers to Trap Surface‐Induced Polymorphs

Enhancing Long‐Term Device Stability Using Thin Film Blends of Small Molecule Semiconductors and Insulating Polymers to Trap Surface‐Induced Polymorphs

Crystal alignment of surface stabilized polymorph in thioindigo films

A New Approach to Polymorphism in Molecular Crystals: Substrate‐Mediated Structures Revealed by Lattice Phonon Dynamics

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