A comprehensive study of a series four‐coordinate boron compounds with the general formula of BPh2(N,N), where N,N are bidentate chelate ligands containing both neutral and negatively charged nitrogen donor atoms has been conducted. The structures of the boron complexes were examined via single‐crystal X‐ray diffraction. The series of molecules display bright luminescence with emission maxima λmax ranging from blue to red, depending on the nature of the N,N chelate ligand. The electronic effects and their consequences on the luminescent properties of the complexes due to the CH replacement of the chelate ligand by a nitrogen atom, the increase of conjugation, or the change of substituents on the chelate ligand have been examined using electrochemical analysis, UV‐visible, and fluorescence spectroscopic methods, and by molecular orbital calculations (Gaussian 98). Experimental data and MO calculation results established that the emission of this class of compounds is caused by π–π* transitions centered on the chelate ligand. Furthermore, the experimental and theoretical results consistently and conclusively established that electron withdrawing groups on the negatively charged N‐donor portion of the chelate ligand causes a decrease in the highest occupied molecular orbital (HOMO) energy level, thus increasing the energy gap. The CH replacement by a nitrogen atom on the negatively charged portion of the chelate ligand causes a dramatic decrease of the HOMO energy level, and the increase of conjugation in the chelate ligand significantly decreases the energy gap. Blue and red electroluminescent (EL) devices were fabricated successfully using two representative boron compounds from the series. The new boron compounds have been found to be able to function as both emitters and electron transport materials in EL devices.

To examine the effect of substituent groups on the luminescence of BPh2(X-2-PI) complexes, three new air-stable boron complexes BPh2(F-2-PI) (5a), BPh2(Cl-2-PI) (5b), and BPh2(CH3O-2-PI) (5c) were synthesized and characterized, where F-2-PI = 5-fluoro-2-(2‘-pyridyl)indole, Cl-2-PI = 5-chloro-2-(2‘-pyridyl)indole, and CH3O-2-PI = 5-methoxyl-2-(2‘-pyridyl)indole. In these complexes, the 5-substituted 2-PI ligand chelates in a tretrahedral fashion to the boron center. Compounds 5a−c are luminescent, with 5a having the highest emission efficiency. Compared with the emission maximum of BPh2(2-PI) (516 nm), the emission maximum of 5a and 5b is blue-shifted to 490 and 487 nm, respectively, while the emission of 5c is red-shifted to 532 nm, indicating the possibility of tuning the luminescence of these complexes by varying the substituent groups on the 2-PI ligand. An electroluminescent device using compound 5a as the emitter and the electron transport material has been fabricated.

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The synthetic scope of the Friedländer condensation in the preparation of chiral alkyl-substituted 1,10-phenanthrolines has been investigated. A range of chiral [x,y-b]-cycloalkeno-condensed phenanthrolines has been prepared in one step from steroidal or other cyclic ketones from the chiral pool and 8-amino-7-quinolinecarbaldehyde (1) via base-catalyzed condensation. Phenanthroline derivatives are formed in good yields with unhindered ketones, but the reaction proceeds even with sterically congested substrates such as camphor, albeit in low yield. The utility of the Friedländer condensation has been extended to the synthesis of chiral 3-alkyl-substituted phenanthrolines from monoalkyl-substituted acetaldehydes.