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

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.