Archetypal donor–acceptor (D–A) interfaces composed of perfluoropentacene (PFP) and pentacene (PEN) are examined for charge transfer (CT) state formation and energetics as a function of their respective molecular configuration. To exclude morphological interference, our structural as well as highly sensitive differential reflectance spectroscopy studies were carried out on PFP thin films epitaxially grown on PEN(001) single-crystal facets. Whereas the experimental data supported by complementary theoretical calculations confirm the formation of a strong CT state in the case of a cofacial PFP–PEN stacking, CT formation is energetically less favorable and thus absent for the corresponding head-to-tail configuration as disclosed for the first time. In view of technological implementations, the knowledge gained on the single-crystal references is transferred to thin-film diodes composed of either stacked PFP/PEN bilayers or mixed PFP:PEN heterojunction interfaces. As demonstrated, their electronic and electroluminescent behavior can be consistently described by the absence or presence of interfacial CT states. Thus, our results hint at the thorough design of D–A interfaces to achieve the highest device performances.

Photo-induced relaxation processes leading to excimer formations or other traps are in the focus of many investigations of optoelectronic materials because they severely affect the efficiencies of corresponding devices. Such relaxation effects comprise inter-monomer distortions in which the orientations of the monomer change with respect to each other, whereas intra-monomer distortions are variations in the geometry of single monomers. Such distortions are generally neglected in quantum chemical investigations of organic dye aggregates due to the accompanied high computational costs. In the present study, we investigate their relevance using perylene-bisimide dimers and diindenoperylene tetramers as model systems. Our calculations underline the importance of intra-monomer distortions on the shape of the potential energy surfaces as a function of the coupling between the monomers. The latter is shown to depend strongly on the electronic state under consideration. In particular, it differs between the first and second excited state of the aggregate. Additionally, the magnitude of the geometrical relaxation decreases if the exciton is delocalized over an increasing number of monomers. For the interpretation of the vibronic coupling model, pseudo-Jahn–Teller or Marcus theory can be employed. In the first part of this paper, we establish the accuracy of density functional theory-based approaches for the prediction of vibrationally resolved absorption spectra of organic semiconductors. These investigations underline the accuracy of those approaches although shortcomings become obvious as well. These calculations also indicate the strength of intra-monomer relaxation effects.

We carried out a comparative study on the excited-state properties of tetracene, which is prone to singlet fission, and its 2,2′ditetracene derivative to analyze the dependence of such loss channels on molecular packing and, thus, intermolecular interactions. In neat single crystals, the absorption and emission spectra of 2,2′-ditetracene are significantly red-shifted by about 150 meV from those of tetracene, while in the case of isolated molecules dispersed in crystalline anthracene matrixes, both dyes show virtually identical emission patterns. Unlike tetracene, the absence of delayed fluorescence in 2,2′-ditetracene single-crystal photoluminescence (PL) and timedependent density functional theory (DFT) calculations based on experimental single-crystal structures indicate a decline in the excited singlet-state energy below the E(S 1 ) = 2E(T 1 ) threshold. Simultaneously, time-resolved temperature-dependent PL data reveal an interplay of the molecular S 1 state and an excited dimer state, which is efficiently populated above 10 K. Upon cooling, the photoluminescence of 2,2′-ditetracene crystals outperforms that of tetracene by more than an order of magnitude and highlights the potential of molecular design, here the covalent linking of two tetracenes, to conserve the optical properties of the individual chromophores while decisively improving their photophysical properties in the crystalline aggregate.

We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivativeg eneratedf rom 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding anys pecific trapping agent, the highly reactiveb enzyne is trapped by anotherb isdiyne molecule in at least three different modes.W eh ave isolated and characterized the resulting products and performed high-level calculations concerning the reactionm echanism. During the cannibalistic self-trapping process, either aC Ct riple bond or an sp-sp 3 CÀCs ingle bond is cleaved. Up to seven rings and nine CÀCb onds are formed startingf rom two 1,11bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experimentsa nd calculations provide considerable insight into the variety of reactionp athways which the ortho-benzyned erivative,g enerated from ab isdiyne, can take when reacting with another bisdiynem olecule.

Doping of semiconductors, such as single-wall carbon nanotubes (SWNTs), by the introduction or removal of charges can be used for modification of their electronic and optical structure. This offers unique opportunities for the fabrication of versatile materials with new properties. However, despite a broad body of work,1−3 the control and spectroscopic assessment of the doping of SWNTs is still being developed4,5 in order to be able to reproducibly tailor semiconductor properties. Here, we have studied the photophysical properties of chemically doped SWNTs by absorption and photoluminescence spectroscopy. Polychiral samples of purified HiPCO soot were charged by oxidation with gold chloride. Thanks to very well-resolved and narrow exciton bands in these samples, the trionic signatures induced by charges could be resolved for up to five distinct nanotube species. An investigation of spectral changes in absorption measurements as a function of gold chloride concentration reveals that tubes with smaller bandgaps are doped at lower gold chloride concentrations. The trion binding energy with respect to the dipole-allowed first sub-band exciton transition was also found to increase systematically with decreasing diameter in agreement with previous findings.1,2 In addition, we find that SWNT oxidation potentials decrease nearly linearly with increasing nanotube diameter. Lastly, a surprisingly abrupt change of exciton oscillator strengths at redox potentials near the nanotube band edge provides evidence for band gap renormalization. References 1. R. Matsunaga, K. Matsuda, Y. Kanemitsu, Phys. Rev. Lett. 2011, 106, 037404. 2. J. S. Park, Y. Hirana, S. Mouri, Y. Miyauchi, N. Nakashima, K. Matsuda, JACS 2012, 134, 14461−14466. 3. S. M. Santos, B. Yuma, S. Berciaud, J. Shaver, M. Gallart, P. Gilliot, L. Cognet, B. Lounis, Phys. Rev. Lett. 2011, 107, 187401. 4. H. Hartleb, F. Späth, T. Hertel, ACS Nano 2015, 9, 10461−10470. 5. M. Yoshida, A. Popert, Y. K. Kato, Phys. Rev. B 2016, 93, 041402.