The 1 L a and 1 L b classification of electronically excited states of cata-condensed hydrocarbons proposed by Platt in 1949 (PlattJ. R. Platt, J. R. J. Chem. Phys.194917484) is challenged by investigating a series of N-heteronaphthalenes and comparison of their low-lying ππ* excited states to those of naphthalene. The breakdown of Platt’s classification scheme for N-heterocycles is highlighted, and a reliable and versatile alternative using exciton analyses is presented. The strength of electron–hole correlation turns out to be the most reliable distinguishing feature, and thus, an alternative nomenclature of 1 L w (weakly correlated) and 1 L s (strongly correlated) is proposed. Furthermore, fundamental guidelines for their property modulation through N-atom substitution patterns are discussed.

In a previous study, we found that one-fold triptycene endcapped quinoxalinophenanthrophenazines (QPPs) arrange in crystals preferably in a coplanar fashion providing high overlap of the π-planes. Thus, resulting in high calculated charge transfer integrals. Most interestingly, this motif was observed for a variety of QPPs derivatives, independently of the nature of their peripheral substituents, e.g. bromide, methoxy, cyano, or triisopropylsilylethynyl groups, and of the crystallization conditions. Here, we describe the synthesis of another small series of three QPPs containing different aromatic substituents at the same position to get an insight, whether these aromatic substituents disturb the otherwise preferred π stacking of the QPP planes. d Intensity ratio between the first and second emission peak.A solution of diamine 1b (14.0 mg, 36.5 µmol) and diketone 2 23 (15.2 mg, 24.4 µmol) in chloroform (1.4 mL) and glacial acetic acid (0.07 mL) was stirred at 70°C under an

Photoswitchable, ambipolar field-effect transistors (FETs) are fabricated with dense networks of polymer-sorted, semiconducting single-walled carbon nanotubes (SWCNTs) in top-gate geometry with photochromic molecules mixed in the polymer matrix of the gate dielectric. Both hole and electron transport are strongly affected by the presence of spiropyran and its photoisomer merocyanine. A strong and persistent reduction of charge carrier mobilities and thus drain currents upon UV illumination (photoisomerization) and its recovery by annealing give these SWCNT transistors the basic properties of optical memory devices. Temperature-dependent mobility measurements and density functional theory calculations indicate scattering of charge carriers by the large dipoles of the merocyanine molecules and electron trapping by protonated merocyanine as the underlying mechanism. The direct dependence of carrier mobility on UV exposure is employed to pattern high- and low-resistance areas within the FET channel and thus to guide charge transport through the nanotube network along predefined paths with micrometer resolution. Near-infrared electroluminescence imaging enables the direct visualization of such patterned current pathways with good contrast. Elaborate mobility and thus current density patterns can be created by local optical switching, visualized and erased again by reverse isomerization through heating.

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymersorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.