Thermally activated delayed fluorescence (TADF) emitters have unique optical and electronic properties owing to the small energy gap between their singlet and triplet excited states. This property of TADF materials allows them to easily undergo interconversion between triplet and singlet states, increases their fluorescence lifetimes, and makes harvesting their excitons much more efficient than other emitters. For these reasons TADF materials show great promise for use in optoelectronic devices such as OLEDs. There has been a growing interest in small organic molecule emitters that feature circularly polarized luminescence emission (CPL-SOMs). These materials allow for development of more advanced optoelectronic devices such as 3D displays, information storage, and in circular dichroism spectroscopy. Recently, a chiral small organic molecule TADF emitter featuring CPL has been developed for use in these applications. Understanding the optoelectronic properties of this CPL-TADF system involves proper treatment of the chemical environment of the molecule. Because solvent and temperature can have a profound effect on the distribution of observed excited-state properties (such as with solvatochromism), it is necessary to perform conformational sampling over the thermally accessible TADF structures. While this sampling can be done using molecular dynamics, obtained excited state properties require quantum mechanical calculations over the large number of structures which can be computationally infeasible. To overcome this challenge, we have used the recently developed effective-stochastic potential time-dependent density functional theory (ESP-TDDFT) method for sampling over 106 conformations of the TADF molecule. The ESP-TDDFT is a finite-temperature quantum chemical method that is capable of calculation ensemble-averaged quantum mechanical properties at finite-temperatures. Using ESP-TDDFT, we have investigated thermal and solvatochromic effects in the UV/VIS spectra for this TADF molecule in several different solvents of differing polarity, including methanol, dichloromethane, and acetonitrile, and the results from this investigation will be presented.

Investigating the effect of solvatochromism in thermally activated delayed fluorescence emitters exhibiting circularly polarized luminescence

2019 Fall National Meeting

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