Exploring Structure–Property Relations of B,S-Doped Polycyclic Aromatic Hydrocarbons through the Trinity of Synthesis, Spectroscopy, and Theory

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are prominent lead structures for organic optoelectronic materials. This work describes the synthesis of three B,S-doped PAHs with heptacene-type scaffolds via nucleophilic aromatic substitution reactions between fluorinated arylborane precursors and 1,2-(Me3SiS)2C6H4/1,8-diazabicyclo­[5.4.0]­undec-7-ene (72–92% yield). All compounds contain tricoordinate B atoms at their 7,16-positions, kinetically protected by mesityl (Mes) substituents. PAHs 1/2 feature two/four S atoms at their 5,18-/5,9,14,18-positions; PAH 3 is a 6,8,15,17-tetrafluoro derivative of 2. For comparison, we also prepared the skewed naphtho­[2,3-c]­pentaphene-type isomer 4. The simultaneous presence of electron-accepting B atoms and electron-donating S atoms results in a redox-ambiphilic behavior; the radical cations [1 • ] + and [2 • ]+ were characterized by electron paramagnetic resonance spectroscopy. Several low-lying charge-transfer states exist, some of which (especially S-to-B and Mes-to-B transitions) compete on the excited-state potential-energy surface. Consistent with the calculated state characters and oscillator strengths, this competition results in a spread of fluorescence quantum yields (2–27%). The optoelectronic properties of 1 change drastically upon addition of Ag+ ions: while the color of 1 in CH2Cl2 changes bathochromically from yellow to red (λmax from 463 to 486 nm; −0.13 eV), the emission band shifts hypsochromically from 606 to 545 nm (+0.23 eV), and the fluorescence quantum yield increases from 12 to 43%. According to titration experiments, higher order adducts [Ag n 1 m ] n+ are formed. As a suitable system for modeling Ag+ complexation, our calculations predict a dimer structure (n = m = 2) with Ag2S4 core, approximately linear S–Ag–S fragments, and Ag–Ag interaction. The computed optoelectronic properties of [Ag2 1 2]2+ agree well with the experimentally observed ones.

TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor‐Acceptor Emitter Featuring a Hybrid Sulfone‐Triarylboron Acceptor**

“…At this point we note that the SO2B acceptor is so strong that it forms a CT state even with the very weak Dipp donor. A similar phenomenon has been observed previously with another very strong organoboron acceptor: 9,10‐dimesityl‐9,10‐dihydro‐9,10‐diboraanthracene [50, 51] . In PXZ‐Dipp‐SO2B and CZ‐Dipp‐SO2B , separation of HOMO and LUMO between the donor and acceptor units (Figure 2) clearly points at a strong CT character of the resultant excited state.…”

TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor‐Acceptor Emitter Featuring a Hybrid Sulfone‐Triarylboron Acceptor**

“…A similar phenomenon has been observed previously with another very strong organoboron acceptor: 9,10-dimesityl-9,10-dihydro-9,10-diboraanthracene. [50,51] In PXZ-Dipp-SO2B and CZ-Dipp-SO2B, separation of HOMO and LUMO between the donor and acceptor units (Figure 2) clearly points at a strong CT character of the resultant excited state. This, in turn, results in a very small 1 CT-3 CT ΔE ST for PXZ-Dipp-SO2B and CZ-Dipp-SO2B, below 0.1 eV, respectively.…”

Recent Advances in Boron‐Containing Acenes: Synthesis, Properties, and Optoelectronic Applications†

“…In addition to the 1,4‐B,X‐doped acenes, in 2022, Wagner and co‐workers developed a series of B,S‐doped heptacenes 82 — 84 with boron and sulfur atoms in different rings. [ 69 ] Interestingly, 82 — 84 exhibited distinct responses to silver ions (Ag + ) by the formation of higher order [Ag n S m ] n + complexes. The complex exhibited a higher PLQY (43%) than that of the free state (12%).…”