Heterofission-induced room temperature phosphorescence from range-separated hybrids: in search of the qualified blending components

Abstract

Heterofission, as the conversion mechanism of a singlet excitation on one chromophore to two triplet excitations on two different chromophores, has been known to play imperative roles to boost the efficiency of photovoltaics. Most recently, the heterofission mechanism has been proposed to explain the room temperature phosphorescence (RTP) of organic materials in the form of host/guest (H/G) systems. Herein, the heterofission-induced RTP in the H/G systems is thoroughly investigated with the help of optimally tuned range-separated hybrid functionals (OT-RSHs). Several experimentally known ultralong RTP H/G systems have been considered as working models. For reliable prediction of the energy level matching criteria for the heterofission-induced RTP in these systems, we have proposed and validated variants of the OT-RSHs, their counterparts based on the linear-response and state-specific formalisms within the polarizable continuum model with both the equilibrium and nonequilibrium solvation regimes, and their screened versions accounting for the screening effects through the scalar dielectric constant. In this line, we scrutinize the role of the related ingredients including the underlying density functional approximations, short-range (α) and long-range Hartree–Fock (HF) exchange, and range-separation parameter. Perusing the results reveals that a particular compromise among the involved parameters is needed for well describing the heterofission-induced RTP. Accordingly, the full time-dependent density functional theory computations in the gas phase using the Perdew–Burke–Ernzerhof (PBE)-based OT-RSH (α = 0.0) with the correct asymptotic behavior in the long-range limit as the best performer are preferred. The proposed method also outperforms the standard RSHs with the default parameters, screened-exchange models, and conventional hybrids with both fixed and interelectronic distance-dependent HF exchange. Lastly, the applicability of our developed approximation is put into broader perspective, where it has been used for computational design of several H/G systems as promising candidates prone to be utilized in heterofission-induced RTP materials. We envisage that the recommended OT-RSH in this study can function as an affordable method for both computational modeling of heterofission-induced RTP and verifying the related experimental observations.