RESEARCHING THE
DIVERSE FUNCTIONSOF ORGANICSEMICONDUCTOR
MATERIALS
CAS SCIFINDER® DOPED THIOPHENEDERIVED ORGANIC SEMICONDUCTORSUSE CASE
Precision search capabilities inCAS SciFinder take you straight torelevant actionable information.

Key emerging organic semiconductors in the multibillion-dollar worldwide electronics industry
Organic semiconductors represent a significant
development in semiconductor technology withwide research interests and extensive potential
applications.1 They offer various advantages
over existing inorganic semiconductors that areused in vital and ubiquitous systems, including;communications, computing, data storage,sensors, control circuits, and photovoltaic cells. 2,3
Organic semiconductors are inexpensive, flexible,environmentally benign, and can be used innumerous applications – even in inkjet inks to create
printed circuits. 3,4 Organic semiconductors are solids
composed of π-bonded molecules or hydrocarbon
polymers and can often contain heteroatoms such as
nitrogen, sulfur, and oxygen. They exist as molecular
crystals or amorphous thin films. These compounds
are largely poor conductors or are electrical insulators
but become semiconducting when charges are either
injected from appropriate electrodes upon doping
or by photoexcitation.

One of the most prominent types of p-type π-conjugatedmaterials are oligothiophenes which have been used
for the core components of both optoelectronic andelectronic devices, including OPVs, OLEDs, and OFETs;
this is largely due to their light-emitting and absorbing,hole transporting, and charge carrier properties. 5
Thiophene-based π-conjugated organic small
molecules and polymers are attracting considerable
research interest due to their potential use as organic
semiconductors in material chemistry. Modifying thechemical structure of thiophene polymers, such asadding side chains, alters the electrical properties ofthese molecules and can produce a diverse range ofsemiconductors. 5 A frequent approach to precise
tuning of semiconductor conductivity is moleculardoping using a range of inorganic or organic
chemicals. 6 One example of polythiophene doping
is with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and related compounds
which substantially increase conductivity and reducethe operation voltage in some systems, one of which
includes small molecule OLEDs. 7-9 Doped thiophenederived semiconductors are therefore likely to play animportant role in increasing the availability, range,and functions of semiconductors within existing andnovel applications.

How can CAS SciFinder support your research in
doped thiophene-derived semiconductors?
Advances in doped thiophene-derived organics are of increasing interest to researchers
who aim to develop novel semiconductors with their desired properties and performance.
The challenge is to identify suitable molecular types and doping agents from a vast range ofcompounds and permutations.
This example shows how you can use SciFinder and the powerful CAS indexing terms to findprecise information and focus your search to address challenges in finding suitable doped
thiophene-derived semiconductors.
The optimal approach to performing this type of search is to start by broadly defining thestructures of the target polymers of interest. These compounds consist of various moieties
containing the thiophene ring or multiple thiophene rings as a basic structural unit:

*

SS

*

SSS
S,,S

To broadly cover these compounds in one search, it is possible to perform a structure search
for thiophene with any substituents at 2nd and 5 th position on the ring. The introduction ofthese substituents is needed to cover the asterisks that mark the end points of the polymer
structure repeating unit in the system and will cover all thiophene molecules of interest.

ASA

CAS SCIFINDER DOPED THIOPHENE USE CASE | 3

The results of a CAS SciFinder search using this strategy are presented below; this has
retrieved a broad and unfiltered set of substances, reactions, and suppliers of compounds
that contain or involve thiophenes as polymers, small organic molecules, and other types ofsubstances, predominantly those containing 2,5-Dimethylthiophene.

In the next stage, the results can be refined using the filters available on the left-hand side of thepage as shown in the image below.
The Substance Class filter has been set to only return polymers within the results set.
Additionally, using the Isotopes filter, it will be set to eliminate substances containing isotopes
considering they are not of direct interest. Finally, the Reference Role filter can further refine theresults to leave only those substances that are discussed with respect to their Uses or Properties.

The Substances page shows 45,126 results, and using the References button, it will returnthe references for this set of substances.

As a result, a set of 32,606 references are retrieved, which will require further refinement.
It is possible to firstly use the available Concepts to retrieve references that are related to
the field of semiconductors through searching for sub-categories that contain the word
stem ‘semiconduct*’ which, when applied, will find all relevant references, and discard
the non-relevant remaining results.

CAS SCIFINDER DOPED THIOPHENE USE CASE | 5

Additional refinement is needed by introducing terms related to ‘doping’ by performing SearchWithin: 'dope or doped or doping'.

This search strategy produced a set of just 6 reviews in the results field, however, it certainly
does not make up the entirety of the reviews available in such a cutting-edge area of research.
The lack of relevant results is subject to substances not usually being indexed in reviews since
there is no additional novelty to these compounds. Moreover, the concepts and other keywords
related to doping may also be missing in the review articles. To overcome this limitation of
our search strategy, it will require tracing back and retrieving all citing documents for this setof highly relevant papers. This alternative strategy can find all the references that were notpreviously returned; it retrieves around 7,000 references that can be refined by document typeto capture all reviews that cite papers on the topic of interest.
This strategy returned 1,078 reviews, and it is even possible to perform a Search Within Results
to eliminate the reviews that are not covering the field of semiconductors, as well as refine theresults by publication year to only include recent publications.

The Concepts filter is an advanced functionality of CAS SciFinder to help you easily refine yourresults and keep your search focused on relevant aspects of the literature. Key scientific terms areadded by CAS indexers from global patents and experimental descriptions of journal articles. Thispowerful indexing allows you to further refine your search to key molecules, doping agents, andassociated technologies currently emerging in doped thiophene semiconductor development.

CAS SCIFINDER DOPED THIOPHENE USE CASE | 7

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References
1. Zhang, Q.; Hu, W.; Sirringhaus, H.; Müllen, K. Recent Progress in Emerging Organic Semiconductors. Advanced Materials. 2022, 34 (22), 2108701. DOI:
10.1002/adma.202108701. 2. The Electrochemical Society. Advancing solid state and electrochemical science and technology. Semiconductors Shaping
Society: Semiconductor applications: From transistors to solar cells. https://www.electrochem.org/semiconductors-shaping-society (accessed 2022-0701). 3. Root, S. E.; Savagatrup, S.; Printz, A. D.; Rodriquez, D.; Lipomi, D. J. Mechanical Properties of Organic Semiconductors for Stretchable, Highly Flexible,and Mechanically Robust Electronics. Chemical Reviews. 2017, 117 (9), 6467–6499. DOI: 10.1021/acs.chemrev.7b00003. 4. Sirringhaus, H.; Kawase, T.; Friend,R. H.; Shimoda, T.; Inbasekaran, M.; Wu, W.; Woo, E. P. High-resolution inkjet printing of all-polymer transistor circuits. Science. 2000, 290 (5499), 2123-2136.
DOI: 10.1126/science.290.5499.2123. 5. Turkoglu, G.; Cinar, M. E.; Ozturk, T. Thiophene-Based Organic Semiconductors. Topics in Current Chemistry. 2017,375 (6). DOI: 10.1007/s41061-017-0174-z. 6. Fujimoto, R.; Yamashita, Y.; Kumagai, S.; Tsurumi, J.; Hinderhofer, A.; Broch, K.; Schreiber, F.; Watanabe, S.;Takeya, J. Molecular doping in organic semiconductors: fully solution-processed, vacuum-free doping with metal–organic complexes in an orthogonalsolvent. Journal of Materials Chemistry C. 2017, 5 (46), 12023-12030. DOI: 10.1039/C7TC03905K. 7. Blochwitz, J.; Pfeiffer, M.; Fritz, T.; Leo. K. Low
voltage organic light emitting diodes featuring doped phthalocyanine as hole transport material. Applied Physics Letters. 1998, 73 (6), 729-731. DOI:
10.1063/1.121982. 8. Aziz, E.F.; Vollmer, A.; Eisebitt, S.; Eberhardt, W.; Pingel, P.; Neher, D.; Koch, N. Localized Charge Transfer in a Molecularly Doped
Conducting Polymer. Advanced Materials. 2007, 19 (20), 3257-3260. DOI: 10.1002/adma.200700926. 9. Valencia, A. M.; Cocchi, C. Electronic and Optical
Properties of Oligothiophene-F4TCNQ Charge-Transfer Complexes: The Role of the Donor Conjugation Length. The Journal of Physical Chemistry C.
2019, 123 (14), 9617–9623. DOI: 10.1021/acs.jpcc.9b01390.

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