Theoretical Studies On The Ground And Excited States Of A Series Of Organoboron Quinolinolates With Extended Conjugated Chromophores

It has been reported in literature that a series of luminescent materials (Ph(2)Bq-x(2)) [x(2)=5,7-dibromo (1); 5,7-diphenyl (2); 5,7-bis(biphenyl-4-yl); 5,7-bis(9,9-dihexylfluoren); q=8-quinolinelate] have been synthesized and investigated. The results showed that the strongest absorption peaks were significantly red-shifted upon the extension of the pi-conjugation length of substituents. Here, di(p-nitrostyryl) (3) and distyryl (4) were introduced to replace bis(biphenyl-4-yl) and bis(9,9-dihexylfiuorenyl), respectively. Density functional theory and time-dependent density functional theory were used to investigate and compare the electronic and spectral properties of complexes I to 4. The calculated results reveal that the two simple substituents can also make the absorption peaks red-shifted following 1 and 2. Furthermore, 3 and 4 have larger oscillator strength at the positions of absorption peaks than those of I and 2, which will increase the transition probability of electrons from the ground state to the excited state. This higher transition probability to the excited state means the greater emission probability.