S. I. Pozin

High precision nanoscale AFM height measurements of J-aggregates

Atomic force microscopy (AFM) was used to obtain high-resolution images of nanosized organic J-aggregate molecular crystals of 3,3′-di(gamma-sulfopropyl)-5,5-dichlorotiamonomethinecyanine (TC) and 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) and precise height measurements of J-aggregates monolayers were conducted. It was found that TC J-aggregates obtained both in the solution bulk and by self-assembly on the mica surface are extended monolayer sheets of high mechanical flexibility. The height of TC is 1.05 ± 0.05 nm, which corresponds to the crystallographic size of a single molecule along the short axis. A model of asymmetric single-layer molecular packing is suggested in which sulfopropyl groups are located on the same side of the layer plane. In the case of C8S3, narrow multilayer ribbonlike structures with heights of 3 to 30 nm were observed. The heights are strictly quantized with a step of 3 nm. A bilayer model of C8S3 molecular packing in J-aggregates is discussed with partially interpenetrating monolayers with hydrophobic sides oriented face to face. A model of structural C8S3 units as “elementary ribbons” with the transverse dimensions of 3 × 4 nm is suggested on the basis of the comparison of AFM data with electron microscopy data from other works.

Tubular structure of J-aggregates of cyanine dye

1 A heightened interest in certain supramolecular organic structures is associated with their unusual optical and electronic properties. These structures include J aggregates of cyanine dyes that represent a variation of micro and nanosized molecular crystals with strong and narrow absorption band (J band) in the visible range shifted toward longer wavelengths as compared with the spectrum of monomers [1, 2]. Owing to high electron–hole conductivity and special spectral properties caused by excitation of delocalized Frenkel excitons, J aggregates are promising organic systems for application in different optoelectronic devices [3–7].

Novel Bipolar Carbazole-Containing Polyphenylquinoxalines: Synthesis and Photophysical Properties

39 In recent time, conjugated electroluminescent polymers have attracted much attention from both the scientific and practical viewpoint due to their application as electroactive materials for light emitting diodes [1–3]. It has been found that intense electroluminescence (EL) in polymer requires high electron–hole conduction of a medium related to the mobility of charge carriers and a balance of injection of carriers of both signs from opposite electrodes into the emission poly meric layer. However, the majority of EL polymers are hole transport materials, which leads to the imbalance of charge injection and a poor quantum yield. A search for new efficient electron transport polymers is required to improve performance of electrooptical devices, which is achieved in particu lar by introducing into macromolecules electron withdrawing fragments: triazole [4], oxadiazole [5], quinoline [6], and quinoxaline [7]. The latter is the least studied. One can suppose that polyphenylqui noxalines (PPQs) will show higher electron with drawing properties owing to the presence of four electron withdrawing heteroatoms. A promising approach to improve the quantum yield is provided not only by the balance of the electron and hole conduction but also by design of multilayer bipolar (donor–acceptor) emission polymers. In this work, to solve this problem, we have used a combination of carbazole and quinoxaline contain ing fragments in PPQ macromolecules. Such mole cules are known to show high thermal and oxidative stability, good mechanical and film forming proper ties, and solubility in organic solvents [8]. In continu ation of our studies [9–11], we have prepared and studied novel bipolar carbazole containing PPQs as efficient electron–hole and transport materials; for this purpose, we obtained previously unknown bis(α diketone) III. A common method for the synthesis of bis(α diketone)s is the oxidation of bis(phenylethy nyl)arenes obtainable from aromatic dibromides and arylacetylene. We have proposed a new method for the synthesis of bis(α diketone) III by the nucleophilic substitution reaction of fluorodiketone II, already containing bis(α dicarbonyl) groups, with dicarbazole I accord ing to Scheme 1. CHEMISTRY

New photoluminescent phenylated polyfluorenes

A new fluorene-containing bis(cyclopentadienone) is synthesized. The interaction of this compound with various diethynylarylenes via the Diels-Alder reaction gives rise to new photoactive phenylated polyfluorenes that emit blue light. Absorption and fluorescence maxima are observed at 330–359 and 394–426 nm, respectively. Polymers show good solubility in organic solvents and possess high chemical resistance and thermal stability.

Crystallography and Molecular Arrangement of Polymorphic Monolayer J-Aggregates of a Cyanine Dye: Multiangle Polarized Light Fluorescence Optical Microscopy Study

The molecular orientation in monolayer J-aggregates of 3,3-di(γ-sulfopropyl)-5,5-dichlorotiamonomethinecyanine dye has been precisely estimated using improved linear polarization measurements in the fluorescence microscope in which a multiangle set of polarization data is obtained using sample rotation. The estimated molecular orientation supplemented with the previously established crystallographic constraints based on the analysis of the well-developed two-dimensional J-aggregate shapes unambiguously indicate the staircase type of molecular arrangement for striplike J-aggregates with the staircases oriented along strips. The molecular transition dipoles are inclined at an angle of ∼25° to the strip direction, whereas the characteristic strip vertex angle ∼45° is formed by the [100] and [1-10] directions of the monoclinic unit cell. Measurements of the geometry of partially unwound tubes and their polarization properties support the model of tube formation by close-packed helical winding of flexible monolayer strips. In the tubes, the long molecular axes are oriented at a small angle in the range of 5-15° to the normal to the tube axis providing low bending energy. At a nanoscale, high-resolution atomic force microscopy imaging of J-aggregate monolayers reveals a complex quasi-one-dimensional organization.

Polymorphism of 2D monolayer J-aggregates of cyanine dyes

Meso- and nanoscale structural polymorphism of monolayer J-aggregates of four cyanine dyes are investigated. Three mesoscale morphological types are observed: ribbons, rhombic leaves, and tubes. Tubes are formed during cylindrical spinning of ribbons. Lined substructure characterized by the line width of about 7 nm is found in the case of monolayers of monomethine cyanine dyes at the nanoscale.

Synthesis and photophysical properties of novel conjugated polymers with 4,5-diaza-9,9 '-spirobifluorene fragments in the main chain

50 Recently, much attention has been paid to polyflu orenes, attractive electroluminescent conjugated polymers, which serve as electroactive materials in polymeric light emitting diodes with blue emission due to the high quantum yield of electroluminescence, mobility of charge carriers, and chemical, thermal, and photostability [1–4]. However, polyfluorenes have several drawbacks resulting from a high injection bar rier between the polymer and the corresponding elec trodes. To improve the injection ability, polyfluorenes were modified by the introduction of electron with drawing heterocyclic fragments [5–8]. However, such a strategy leads to the strong violation of structural fea tures of the polymer chain and, hence, to the degrada tion of physical properties of materials. These difficul ties were surmounted by the synthesis of multifunc tional fluorene containing different functional groups at the 9 position [9–12].