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Boron‐Doped Tri(9,10‐anthrylene)s: Synthesis, Structural Characterization, and Optoelectronic Properties
Author(s) -
Hoffend Claas,
Schödel Frauke,
Bolte Michael,
Lerner HansWolfram,
Wagner Matthias
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202280
Subject(s) - moiety , chemistry , dihedral angle , stereochemistry , molecule , solid state , double bond , boron , homo/lumo , crystallography , atropisomer , medicinal chemistry , polymer chemistry , organic chemistry , hydrogen bond
The reaction of 9,10‐dibromo‐9,10‐dihydro‐9,10‐diboraanthracene (9,10‐dibromo‐DBA, 3 ) with two equivalents of 9‐lithio‐2,6‐ or 9‐lithio‐2,7‐di‐ tert ‐butylanthracene gave the corresponding 9,10‐dianthryl‐DBAs featuring two ( 4 ) or four ( 5 ) inward‐pointing tert ‐butyl groups. Compound 4 exists as two atropisomers, 4 and 4′ , due to hindered rotation about the exocyclic BC bonds. X‐ray crystallography of 5 suggests that the overall interactions between facing tert ‐butyl groups are attractive rather than repulsive. Even in solution, 4 / 4′ and 5 are stable toward air and moisture for several hours. Treatment of 3 with 10‐lithio‐9‐R‐2,7‐di‐ tert ‐butylanthracenes carrying phenyl (R=Ph), dimesitylboryl (R=Mes 2 B), or N , N ‐di( p ‐tolyl)amino (R=Tol 2 N) groups gave the corresponding 9,10‐dianthryl‐DBA derivatives 9 – 11 in moderate to good yields. In these molecules, all four solubilizing tert ‐butyl groups are outward pointing. The solid‐state structures of 4 , 5 , 9 , and 10 reveal twisted conformations about the exocyclic BC bonds with dihedral angles of 70–90°. A significant electron‐withdrawing character was proven for the Mes 2 B moiety, but no appreciable +M effect was evident for Tol 2 N. Compounds 5 , 9 , and 11 show two reversible DBA‐centered reduction waves in the cyclic voltammogram. In the case of 10 , a third reversible redox transition can be assigned to the Mes 2 B–anthryl substituents. The UV/Vis absorption spectrum of 5 is characterized by a very broad band at λ max =510 nm, attributable to a twisted intramolecular charge‐transfer interaction from the anthryl donors to the DBA acceptor. The corresponding emission band shows pronounced positive solvatochromism ( λ em =567 nm, C 6 H 12 ; 680 nm, CH 2 Cl 2 ) in line with a highly polar excited state. The charge‐transfer bands of 10 and 11 , as well as the emission bands of 9 and 10 , are redshifted relative to those of 5 . The Tol 2 N derivative 11 is essentially nonfluorescent in solution, but emits bright wine‐red light in the solid state.