Conformational Planarization versus Singlet Fission: Distinct Excited‐State Dynamics of Cyclooctatetraene‐Fused Acene Dimers

Abstract

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Using Structurally Well-Defined Norbornyl-Bridged Acene Dimers to Map a Mechanistic Landscape for Correlated Triplet Formation in Singlet Fission

“…In one of these, dimer connectivity occurs via the chromophore ends either using single bonds through the acene 2 position 5,11 or using bicyclic moieties that connect simultaneously through the 2 and 3 positions. 14,17,18 This latter group includes the [2.2.1]-bridge dimer TIPS-BP1' (see Fig. 1) discussed herein whose synthesis and preliminary photophysics were recently reported by us.…”

“…Understanding how to control such dynamics is motivated by the premise that SF may serve as a means to down-convert higher energy solar photons into multiple electronic excitations rather than into a single excitation plus waste heat. 3 Dimer and small oligomer systems using acenes, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] but also diimides, 20 and isobenzofurans 21,22 are enabling the interrogation of numerous fundamental issues affecting SF rates and yields, including reaction thermodynamics, 6,[16][17][18]23 state couplings, 8,9,21,24,25 charge transfer intermediates, 10,[19][20][21] the role of entropy, 8 spin dynamics, 15,26 and exciton binding. 8,22,27 Within the overall body of dimer work in the literature, a leading role has been played by pentacene-based systems [5][6][7][10][11]…”

Facile Synthesis of Dibenzotetracenedione Derivatives by Rhodium‐Catalyzed [2+2+2] Cycloaddition/Spontaneous Aromatization

“…This dibenzotetracenes howed blue fluorescencew ith ag ood quantum yield, which was significantly higher than that of the fluorescence quantum yields of 6, 7,and 8. 1f, [20] 1g, [9c] and 1h, [9d] and 2b [21] were prepared according to procedures reported in the literature. All other reagents were obtained from commercial sources and used as received.…”

Amine‐Substituted Diazocine Derivatives – Synthesis, Structure, and Photophysical Properties

“…Although diazocine compounds did not undergo planarization on two-electron reduction, it may be possible for these compounds to achieve a planarized geometry in their excited state, a phenomenon reported previously in a cyclooctatetraene system. [3,27,28] As a comparison with the solution spectra, the photoluminescence spectrum of both 1g and 2g in poly(methyl methacrylate) film was acquired. It was expected that the emission would primarily come from the carbazole at 358 nm with little or no longer wavelength emission because of the restriction of molecular dynamics in the solid matrix.…”

“…This can be achieved by performing more detailed spectroscopic studies in different polarity solvents and in a range of temperatures as well as excited state absorption and lifetime experiments. [27,28] DFT Calculations can also be used to support the experimental evidence for excited state planarization. [27,28] Further derivatization of the diazocine building block can also be explored with the aim of achieving reversible two-electron reduction.…”