Controlling the Optoelectronic Properties of Pyrene by Regioselective Lewis Base‐Directed Electrophilic Aromatic Borylation

Abstract

Given that pyrene represents one of the most versatile chromophores, the development of new selective routes for its functionalization and tuning of its emission properties is highly desirable. Pyrene‐based BN Lewis pair (LP)‐functionalized polycyclic aromatic hydrocarbons (PAHs) were prepared by regioselective Lewis base‐directed electrophilic aromatic substitution. The requisite 1,6‐dipyridylpyrene ligands were accessed by Suzuki–Miyaura cross‐coupling of 1,6‐bis(pinacolatoboryl)pyrenes with 2‐bromopyridine derivatives. Subsequent electrophilic borylation with BCl3 in the presence of AlCl3 and 2,6‐di‐tert‐butylpyridine as a hindered base produced the dichloroborane complexes, which were then in situ reacted with diphenyl or diethyl zinc. The presence or absence of alkyl chains in the 3,8‐positions of the pyrene moiety determined the position of the B−C bond formation (2,7 in the non‐K region versus 5,10 in the K region) and thereby also the size of the BN heterocycle (five‐ versus six‐membered). The impact of the regioisomeric borylation on the electrochemical, photophysical and structural properties was investigated and the conclusions supported by theoretical calculations. The rapid synthesis of derivatives that are borylated in the K region also suggests strong potential for the development of pyrene derivatives that are otherwise difficult to access.

The synthesis of brominated-boron-doped PAHs by alkyne 1,1-bromoboration: mechanistic and functionalisation studies

“…Scheme 6 The formation of extended B n -PAHs by bromoboration/ S E Ar. isomer E red1 1/2 ¼ À2.31 V, 1,6 isomer E red1 1/2 ¼ À1.81 V) 11 and the products from the electrophilic borylation of 1,6-(2-pyridyl) 2pyrene (when the boron moiety ¼ BPh 2 E red1 1/2 ¼ À2.08 V) 14 this is ascribed to greater p delocalization in 9a as a result of planarization and three-coordinate B centres. Finally, 9a has a more positive reduction potential than its all carbon analogue (for which E red1 1/2 ¼ À2.11 V), 15 further conrming boron-doping as an effective strategy to obtain molecules with deep LUMOs due to their electron-decient nature (B 2 -PAHs are isoelectronic to dicationic carbon analogues).…”

Linear Extension of Anthracene via B←N Lewis Pair Formation: Effects on Optoelectronic Properties and Singlet O2Sensitization

“…Similar to the case of 1‐pyridylnaphthalene, the borylation of 9,10‐dipyridylanthracene using BCl 3 /AlCl 3 /2,6‐di‐ t ‐butylpyridine (DBP) proceeds preferentially in the peri‐positions to generate a product with 6HCs [10b,d] . Finally, the borylation of 1,6‐dipyridylpyrene occurs in the 2,7‐positions but can be redirected into the 5,10‐ positions (K‐region) by introducing alkyl groups to block the attack in the 2,7‐positions [10e] …”

B←N Coordination: From Chemistry to Organic Photovoltaic Materials

“…Using a similar synthetic strategy, they also synthesized two regioisomeric structures containing B←N bonds based on pyrene (40 and 41). [ 89 ] For both Ph and Et substitutions, the six‐member‐contained units (41) show largely red‐shifted absorption and emission maxima relative to the five‐member‐contained units (40).…”