From red to green luminescence via surface functionalization. Effect of 2-(5-mercaptothien-2-yl)-8-(thien-2-yl)-5-hexylthieno[3,4-c]pyrrole-4,6-dione ligands on the photoluminescence of alloyed Ag-In-Zn-S nanocrystals

A semiconducting molecule containing a thiol anchor group, namely 2-(5-mercaptothien-2-yl)-8-(thien-2-yl)-5-hexylthieno- [3,4-c]pyrrole-4,6-dione (abbreviated as D-A-D-SH), was designed, synthesized, and used as a ligand in nonstoichiometric quaternary nanocrystals of composition Ag1.0In3.1Zn1.0S4.0(S6.1) to give an inorganic/organic hybrid. Detailed NMR studies indicate that D-AD- SH ligands are present in two coordination spheres in the organic part of the hybrid: (i) inner in which the ligand molecules form direct bonds with the nanocrystal surface and (ii) outer in which the ligand molecules do not form direct bonds with the inorganic core. Exchange of the initial ligands (stearic acid and 1-aminooctadecane) for D-A-DSH induces a distinct change of the photoluminescence. Efficient red luminescence of nanocrystals capped with initial ligands (λmax = 720 nm, quantum yield = 67%) is totally quenched and green luminescence characteristic of the ligand appears (λmax = 508 nm, quantum yield = 10%). This change of the photoluminescence mechanism can be clarified by a combination of electrochemical and spectroscopic investigations. It can be demonstrated by cyclic voltammetry that new states appear in the hybrid as a consequence of D-A-D-SH binding to the nanocrystals surface. These states are located below the nanocrystal LUMO and above its HOMO, respectively. They are concurrent to deeper donor and acceptor states governing the red luminescence. As a result, energy transfer from the nanocrystal HOMO and LUMO levels to the ligand states takes place, leading to effective quenching of the red luminescence and appearance of the green one

Azaacenes Based Electroactive Materials: Preparation, Structure, Electrochemistry, Spectroscopy and Applications—A Critical Review

This short critical review is devoted to the synthesis and functionalization of various types of azaacenes, organic semiconducting compounds which can be considered as promising materials for the fabrication of n-channel or ambipolar field effect transistors (FETs), components of active layers in light emitting diodes (LEDs), components of organic memory devices and others. Emphasis is put on the diversity of azaacenes preparation methods and the possibility of tuning their redox and spectroscopic properties by changing the C/N ratio, modifying the nitrogen atoms distribution mode, functionalization with electroaccepting or electrodonating groups and changing their molecular shape. Processability, structural features and degradation pathways of these compounds are also discussed. A unique feature of this review concerns the listed redox potentials of all discussed compounds which were normalized vs. Fc/Fc+. This required, in frequent cases, recalculation of the originally reported data in which these potentials were determined against different types of reference electrodes. The same applied to all reported electron affinities (EAs). EA values calculated using different methods were recalculated by applying the method of Sworakowski and co-workers (Org. Electron. 2016, 33, 300–310) to yield, for the first time, a set of normalized data, which could be directly compared

Indanthrone dye revisited after sixty years

Indanthrone, an old, insoluble dye can be converted into a solution processable, self-assembling and electroluminescent organic semiconductor, namely tetraoctyloxydinaptho[2,3-a:20,30-h]phenazine (P-C8), in a simple one-pot process consisting of the reduction of the carbonyl group by sodium dithionite followed by the substitution with solubility inducing groups under phase transfer catalysis condition

Anchor Groups Effect on Spectroscopic and Electrochemical Properties of Quaternary Nanocrystals Cu–In–Zn–S Capped with Arylamine Derivatives

A two-step procedure is reported enabling preparation of quaternary Cu–In–Zn–S nanocrystals with electrochemically active ligands consisting of 4-dodecylphenylaminobenzene and amine, thiol, or carboxylic anchor groups. Detailed ¹H NMR and IR studies of nanocrystals dispersion as well as free ligands recovered via nanocrystals dissolution indicate that in the organic shell of initial ligands weakly (1-octadecene (ODE)) and more strongly (1-dodecanethiol (DDT) and oleylamine (OLA)) bound ligands coexist. Treating the nanocrystals with pyridine removes weakly bound ligands; however, DDT and OLA molecules remain present as coligands with pyridine. Labile pyridine ligands can then be exchanged for the target 4-dodecylphenylaminobenzene derivatives with different anchor groups. ¹H NMR lines of these ligands are broadened due to their restricted rotation; this broadening is especially pronounced for the lines corresponding to the anchor group protons. Electrochemical activity of the ligands is significantly altered after their binding to the nanocrystal surface. Strongly interacting anchor groups such as −Ph–SH or −Ph–CH₂NH₂ lose their electrochemical activity upon coordination to nanocrystals, and weakly interacting groups (−PhNH₂) retain it. Secondary amine −Ph–NH–Ph– remains electrochemically active in all nanocrystals capped with the studied ligands; however, the potential of its oxidation depends on the conjugation with the anchor group

Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light-Emitting Diodes

Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione, an old and almost-forgotten vat dye, by reduction of its carbonyl groups and subsequent O-alkylation, yields solution-processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and −3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16-dioctyloxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine (FC-8), the most promising compound, was solved. It crystallizes in space group Pmath formula and forms π-stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC-8 have a strong tendency to self-organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16-Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl host in guest/host-type organic light-emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m−12, a luminance efficiency of about 3 cd A−1, and external quantum efficiencies exceeding 0.9 %

Self-Assembly Properties of Semiconducting Donor–Acceptor–Donor Bithienyl Derivatives of Tetrazine and ThiadiazoleEffect of the Electron Accepting Central Ring

Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituent’s position on the type and extent of 2D supramolecular organization of penta-ring donor–acceptor–donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituent’s position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates

Structural, Spectroscopic, Electrochemical, and Electroluminescent Properties of Tetraalkoxydinaphthophenazines: New Solution-Processable Nonlinear Azaacenes

A series of solution-processable tetraalkoxy-substituted dinaphtho­[2,3-<i>a</i>:2′,3′-<i>h</i>]­phenazines were synthesized by reductive functionalization of indanthrone (6,15-dihydrodinaphtho­[2,3-<i>a</i>:2′,3′-<i>h</i>]­phenazine-5,9,14,18-tetraone), an old intractable dye. The melting point of these new compounds was found to decrease from 204 °C to 98 °C upon extension of the number of carbons from 4 to 12 in the alkoxy substituent. All derivatives show a strong tendency to self-organize in 2D as evidenced by STM investigations of monolayers deposited on HOPG. The 2D structure is less dense and shows different alkoxy group interdigitation pattern as compared to the 3D structure determined from the X-ray diffraction data obtained for the corresponding single crystals. Electrochemical, absorption, and emission properties of tetraalkoxy-substituted dinaphtho­[2,3-<i>a</i>:2′,3′-<i>h</i>]­phenazines, studied in solution, are essentially independent of the length of the alkoxy substituents. All derivatives exhibit high photoluminescence quantum yield, approaching 60%. When molecularly dispersed in a solid matrix consisting of poly­(9-vinylcarbazole) (PVK) (60 wt %) and (2-<i>tert</i>-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) (40 wt %) (so-called “guest/host configuration”), they show green electroluminescence due to an effective energy transfer from the matrix to the luminophore. The best light-emitting diodes were obtained for the butoxy derivative showing a luminance approaching 1500 cd/m² and a luminous efficiency over 0.8 cd/A