Molecular engineering of organic semiconductors enables noble metal-comparable SERS enhancement and sensitivity

Nanostructured molecular semiconductor films are promising Surface-Enhanced Raman Spectroscopy (SERS) platforms for both fundamental and technological research. Here, we report that a nanostructured film of the small molecule DFP-4T, consisting of a fully π-conjugated diperfluorophenyl-substituted quaterthiophene structure, demonstrates a very large Raman enhancement factor (>105) and a low limit of detection (10-9 M) for the methylene blue probe molecule. This data is comparable to those reported for the best inorganic semiconductor- and even intrinsic plasmonic metal-based SERS platforms. Photoluminescence spectroscopy and computational analysis suggest that both charge-transfer energy and effective molecular interactions, leading to a small but non-zero oscillator strength in the charge-transfer state between the organic semiconductor film and the analyte molecule, are required to achieve large SERS enhancement factors and high molecular sensitivities in these systems. Our results provide not only a considerable experimental advancement in organic SERS figure-of-merits but also a guidance for the molecular design of more sensitive SERS systems

A modified artificial bee colony algorithm for numerical function optimization

Artificial bee colony (ABC) algorithm, explored in recent literature, is an efficient optimization technique which simulates the foraging behavior of honeybees. ABC algorithm is good at exploration but poor at exploitation. This paper presents a new modified ABC algorithm for numerical optimization problems to improve the exploitation capability of the ABC algorithm. A different probability function and a new searching mechanism are proposed. The modified ABC algorithm is tested on seven numerical optimization problems. The results demonstrate that the modified ABC algorithm outperforms the ABC algorithm on solution quality and faster convergence

Quantum dot patterning and encapsulation by maskless lithography for display technologies

For their unique optical properties, quantum dots (QDs) have been extensively used as light emitters in a number of photonic and optoelectronic applications. They even met commercialization success through their implementation in high -end displays with unmatched brightness and color rendering. For such applications, however, QDs must be shielded from oxygen and water vapor, which are known to degrade their optical properties over time. Even with highly qualitative QDs, this can only be achieved through their encapsulation between barrier layers. With the emergence of mini-and microLED for higher contrast and miniaturized displays, new strategies must be found for the concomitant patterning and encapsulation of QDs, with sub-millimeter resolution. To this end, we developed a new approach for the direct patterning of QDs through maskless lithography. By combining QDs in photopolymerizable resins with digital light processing (DLP) projectors, we developed a versatile and massively parallel fabrication process for the additive manufacturing of functional structures that we refer to as QD pockets. These 3D heterostructures are designed to provide isotropic encapsulation of the QDs, and hence prevent edge ingress from the lateral sides of QD films, which remains a shortcoming of the current technologies

Organic Light-Emitting Physically Unclonable Functions

The development of novel physically unclonable functions (PUFs) is of growing interest and fluorescent organic semiconductors (f-OSCs) offer unique advantages of structural versatility, solution-processability, ease of processing, and great tuning ability of their physicochemical/optoelectronic/spectroscopic properties. The design and ambient atmosphere facile fabrication of a unique organic light-emitting physically unclonable function (OLE-PUF) based on a green-emissive fluorescent oligo(p-phenyleneethynylene) molecule is reported. The OLE-PUFs have been prepared by one-step, brief (5 min) thermal annealing of spin-coated nanoscopic films (approximate to 40 nm) at a modest temperature (170 degrees C), which results in efficient surface dewetting to form randomly positioned/sized hemispherical features with bright fluorescence. The random positioning of molecular domains generated the unclonable surface with excellent uniformity (0.50), uniqueness (0.49), and randomness (p > 0.01); whereas the distinctive photophysical and structural properties of the molecule created the additional security layers (fluorescence profile, excited-state decay dynamics, Raman mapping/spectrum, and infrared spectrum) for multiplex encoding. The OLE-PUFs on substrates of varying chemical structures, surface energies and flexibility, and direct deposition on goods via drop-casting are demonstrated. The OLE-PUFs immersed in water, exposed to mechanical abrasion, and read-out repeatedly via fluorescence imaging showed great stability. These findings clearly demonstrate that rationally engineered solution-processable f-OSCs have a great potential to become a key player in the development of new-generation PUFs

Interplay between Charge Injection, Electron Transport, and Quantum Efficiency in Ambipolar Trilayer Organic Light-Emitting Transistors

The fascinating characteristic of organic light-emitting transistors (OLETs) of being electrical switches with an intrinsic light-emitting capability makes them attractive candidates for a wide variety of applications, ranging from sensors to displays. To date, the OLET ambipolar trilayer heterostructure is the most developed architecture for maximizing device performance. However, a major challenge of trilayer OLETs remains the inverse correlation between external quantum efficiency and brightness under ambipolar conditions. The complex interconnection between electroluminescent and ambipolar charge transport properties, in conjunction with the limited availability of electron transport semiconducting materials, has indeed hampered the disruptive evolution of the OLET technology. Here, an in-depth study of the interplay of the key fundamental features that determine the device performance is reported by exploring electron transport semiconductors with different properties in ambipolar trilayer OLETs. Through the selection of compounds with tailored chemical structures, the relation between intrinsic optoelectronic characteristics of the electron transport semiconductor, energy level alignment within the structure, and morphological features is unraveled. Furthermore, the introduction of a suitable electron injector at the emissive/semiconducting layers interface sheds light into the bidimensional nature of OLETs that is a distinguishing factor of this class of devices with respect to prototypical organic light-emitting diodes.Funding Agencies|European Unions Horizon 2020 Research and Innovation Programme [101016706]</p

CCDC 288774: Experimental Crystal Structure Determination

Related Article: Joseph A. Letizia, Antonio Facchetti, Charlotte L. Stern, Mark A. Ratner, Tobin J. Marks|2005|J.Am.Chem.Soc.|127|13476|doi:10.1021/ja054276o,Related Article: Gokhan Demirel, Rebecca L. M. Gieseking, Resul Ozdemir, Simon Kahmann, Maria A. Loi, George C. Schatz, Antonio Facchetti, Hakan Usta|2019|Nat.Commun.|10||doi:10.1038/s41467-019-13505-7

CCDC 207396: Experimental Crystal Structure Determination

Related Article: A.Facchetti, Myung-Han Yoon, C.L.Stern, H.E.Katz, T.J.Marks|2003|Angew.Chem.,Int.Ed.|42|3900|doi:10.1002/anie.200351253,Related Article: Myung-Han Yoon, A.Facchetti, C.E.Stern, T.J.Marks|2006|J.Am.Chem.Soc.|128|5792|doi:10.1021/ja060016a,Related Article: Gokhan Demirel, Rebecca L. M. Gieseking, Resul Ozdemir, Simon Kahmann, Maria A. Loi, George C. Schatz, Antonio Facchetti, Hakan Usta|2019|Nat.Commun.|10||doi:10.1038/s41467-019-13505-7