The coordination number–photophysical properties relationship of trianthrylphosphorus compounds: doubly locked fluorescence of anthryl groups

A series of tri(9-anthryl)phosphorus compounds including tri(9-anthryl)methylphosphonium iodide (2b), tri(9-anthryl)phophine oxide (2c), and tri(9-anthryl)difluorophosphorane (2d) have been newly synthesized from the already reported tri(9-anthryl)phosphine (2a) and their photophysical properties including UV–vis absorption and fluorescence spectra have been determined in order to elucidate their coordination number–properties relationships. It has been found that their characteristic fluorescence properties are highly dependent on the coordination number of the central phosphorus atom. Thus, while the tri-coordinate phosphine 2a and the tetra-coordinate phosphonium salt 2b and phosphine oxide 2c show no and weak (Φf<0.01) fluorescence, respectively, the penta-coordinate phosphorane 2d exhibits intense fluorescence (Φf=0.28) which is comparable to that of the parent anthracene.