How Boron Doping Shapes the Optoelectronic Properties of Canonical and Phenylene‐Containing Oligoacenes: A Combined Experimental and Theoretical Investigation

Abstract

Optimized syntheses of 6,13-dimesityl-6,13-dihydro-6,13-diborapentacene (DBP) and a related compound (DBI) featuring two biphenylene-2,3-diyl units in place of naphthalene-2,3-diyl moieties are reported. Striking differences between the optoelectronic properties of DBP and DBI have been experimentally observed, and explained by quantum chemical calculations. DBP is a member of the oligoacene family, DBI is a linear [N]phenylene derivative. The yellow DBP shows blue photoluminescence, the deep red DBI is nonfluorescent. Both compounds give rise to two reversible redox transitions at E1/2 =-2.03 V, -2.75 V (DBP) and -1.52 V, -2.30 V (DBI; THF, vs. FcH/FcH ). The higher electron affinity of DBI agrees with a lower calculated LUMO energy level [-0.57 eV for DBI with respect to DBP @HF//SCS-MP2/def2-TZVP] and a higher Lewis acidity of its boron centers, which is reflected in the trend of adduct formation with small Lewis bases (MeCN, F ). The thermochemistry underlying this trend, as well as the mechanism of fluorescence quenching in DBI, are revealed by state-of-the-art quantum chemical calculations. It is suggested that the nonradiative deactivation occurs via a low-lying, doubly excited state.

C‐Halogenated 9,10‐Diboraanthracenes: How the Halogen Load and Distribution Influences Key Optoelectronic Properties

“…The currently most practical synthesis routes to DBAs are summarized in Scheme . Cyclocondensation (“CC”) of 1,2‐(Me 3 Si) 2 ‐benzene with BBr 3 at an elevated temperature of 120 °C over 72 h affords 9,10‐(Br) 2 ‐DBA (X=H; Y=Br; hexane, thick‐walled glass ampule) . Derivatization of the bromoborane at its two boron atoms is facile, for example, with organolithium or Grignard compounds.…”

“…The shoulders/weak bands are thus most likely due to intramolecular charge transfer (ICT) transitions from the mesityl rings to the DBA π* systems, whereas the dominant bands correspond to locally excited DBA π–π* transitions. This assumption is not only supported by quantum chemical calculations on related systems, but also by the following experimental facts (Figure ): (i) a comparison of the UV/Vis spectrum of 7 and its 9,10‐(Me) 2 analog 7 Me shows almost identical main absorptions; the bathochromic shoulder, however, is entirely missing in the spectrum of 7 Me . (ii) The emission band of 7 Me appears at significantly smaller wavelengths ( λ em =420 nm) than that of 7 ( λ em =488 nm), because the former is a mirror image of the π–π* absorption, while the latter is a mirror image of the ICT absorption.…”

“…Despitet he recent progress in the field, comprehensive insight into key structure-property relationships of B-PAHs is still lacking, because the required access to entire series of system-atically modulatable B-PAH derivatives still imposes af ormidable challenge to the synthetic chemist. [4][5][6] Herein, we report an array of halogenated 9,10-dihydro-9,10-diboraanthracenes (DBAs; Figure 1), which differ in the nature (i.e., 1/5, 2/3/6, 4/7)o rt he numbersa nd positions of their halogen substituents( i.e., [5][6][7][8][9][10]. In all cases, compound I serves as the benchmark for comparison purposes.…”

Exploiting the Strong Hydrogen Bond Donor Properties of a Borinic Acid Functionality for Fluoride Anion Recognition

“…This data suggests that the biphenylene substituent is electron withdrawing, [13] ac onclusion consistent with ar ecent paper by Wagner and co-workers on 2,3-borylated biphenylene derivatives. [14] As imilar conclusion can be derived from the CV of the model compound 1-dimesitylborylbiphenylene (3), which we synthesized for the sake of comparison (see the Supporting Information). This compound shows aq uasireversible reduction wave at À2.37 V, which is anodically shifted by 350 mV from that of Mes 3 B.…”

Exploiting the Strong Hydrogen Bond Donor Properties of a Borinic Acid Functionality for Fluoride Anion Recognition

“…Fc/ Fc + ,thus suggesting that the molecule can be reduced by two electrons.I ti si nteresting to note that the potential of the first reduction is shifted to anodic potentials by 490 mV when compared to the reduction potential of Mes 3 B( À2.72 V). [14] As imilar conclusion can be derived from the CV of the model compound 1-dimesitylborylbiphenylene (3), which we synthesized for the sake of comparison (see the Supporting Information). [14] As imilar conclusion can be derived from the CV of the model compound 1-dimesitylborylbiphenylene (3), which we synthesized for the sake of comparison (see the Supporting Information).…”