Theoretical investigation on the photophysical properties of N-heterocyclic carbene iridium (III) complexes (fpmb)(x)Ir(bptz)(3-x) (x = 1-2).

In the search for efficiently phosphorescent materials, this article presents a rational design and theoretical comparative study of some photophysical properties in the (fpmb)(x)Ir(bptz)(3-x) (x = 1-2), which involve the usage of two 2-pyridyl triazolate (bptz) chromophores and a strong-field ligand fpmb (fpmb = 1-(4-difluorobenzyl)-3-methylbenzimidazolium). The first principle theoretical analysis under the framework of the time-dependent density functional theory approach is implemented in this article to investigate the electronic structures, absorption and phosphorescence spectra. It is intriguing to note that 1 and 2 exhibit theirs blue phosphorescent emissions with maxima at 504 and 516 nm, respectively. Furthermore, to obtain the mechanism of low phosphorescence yield in 1 and estimate the radiative rate constant k(r) for 2, we approximately measure the radiative rate constant k(r), the spin-orbital coupling (SOC) value, ΔE (S - T), and the square of the SOC matrix element (<Ψ(S1·)H(SO·)Ψ(T1)>(2)) for 1 and 2. Finally, we tentatively come to conclusion that the switch of the cyclometalated ligand from the main to ancillary chelate seems to lower the splitting ΔE (S - T) in the current system.