A series of 1,4-phenylenes X-C6H4 BDB featuring one 1,3,2-benzodiazaborolyl (BDB) and a phosphorus-based end group [X= PPh2 (HK1 & HK2), P(O)Ph2 (HK1=O), P(S)Ph2 (HK1=S), P(Se)Ph2 (HK1=Se), P(AuCl)Ph2 (HK1 AuCl) and P(Me)Ph2 (HK1 Me)] as well as 2-(2’)thienyl-1,3,2-benzodiazaboroles with a second end group X [X= PPh2 (HK3 & HK4), P(S)Ph2 (HK3=S), P(Se)Ph2 (HK3=Se) and P(Me)Ph2 (HK3 Me)] in the 5’ position are presented. Their syntheses, analytical and molecular structures as well as their optical properties are discussed. The experimental data are accompanied by theoretical TD-DFT computations (B3LYB/G-311G(d,p)) to further increase the understanding of the optical properties of this series of compounds. The phosphanes HK1, HK2, HK3 and HK4 show no significant luminescence but are converted via photo-oxidation into their corresponding oxides.

The derivatives HK1=O, HK1=S, HK1-AuCl, HK1-Me, HK3=S and HK3-Me show intense blue luminescence in cyclohexane, toluene, chloroform, tetrahydrofuran and dichloromethane solutions with a pronounced solvatochromism. Thereby, the Stokes shifts are varying between 8950- and 10440 cm-1 in dichloromethane solution and mirror the nature of the phosphorus based end group. The phosphonium compounds HK1-Me and HK3-Me show the largest Stokes shift in this series. Quantum yields up to 0.70 are observed for these compounds, whereby the quantum yields of the selenium derivatives (HK1=Se, HK3=Se), however, are quite small (<0.1).

A second series of compounds represented by different phosphonium salts of the type aryl-CH2-P(Ph2)-C6H4-BDB including the 1,3,2-benzodiazaborolyl-unit (BDB) and different aryl-groups [aryl= anthracen (HK1-Anthra), phenyl (HK1-Benzyl), PhF5 (HK1-FBenzyl)] as well as one thienyl-analogue of the anthracen compound (HK3-Anthra) is presented. Unfortunately these compounds proved to be quite unstable towards UV-irradiation.

To avoid the potentially reactive CH2-bridge between the phosphorus atom and the aryl system a triphenyl-phosphonium compound of the type Ph3P-C6H4-BDB (HK1 Phenyl) was synthesized and proved to be photochemically more stable.