Correlation between the Intrinsic Photophysical Properties of the Spirobifluorene-Derived Monomer

Abstract

Spiro-molecules derived from the functional spirobifluorene core play important roles in the frontiers of diverse optoelectronics. The optoelectronics of these molecules have been intensively studied without yielding a knowledge base of precisely parameterized photophysical properties. Here, we report the precisely parameterized photophysics of spiro-OMeTAD, one prototypical optoelectronic spirobifluorene derivative. The use of a preobtained single-crystalline pure spiro-OMeTAD solid for the solution preparation allows for accurate determination of its molar absorption coefficient (ϵ) in its monomer form. A near-unity photoluminescence quantum yield (φL ∼99%) was observed from the monomer solution. The monomer's photoluminescence decay follows a mono-exponential channel that results in a lifetime (τ) of ∼1.64 ns. Taken together ϵ, φL, and τ correlate well via the Strickler-Berg equation. The Strickler-Berg relationship among the key photophysical properties determined on spiro-OMeTAD applies for spirobifluorene derivatives, as verified in an extended test on the newly created spiro-mF. Practical issues that may lead to misparameterized photophysical properties of these molecules are emphasized. Our results of the precisely parameterized photophysical properties of the spiro-OMeTAD monomer in dilute solution serve as background references for studying the optoelectronic processes in the technically more useful thin-film form in practical optoelectronic devices.