\chapter*{SKYRIAUS PAVADINIMAS}
\addcontentsline{toc}{chapter}{TURINY SKYRIAUS PAVADINIMAS}

This chapter will introduce the reader to the basics of thermally activated delayed fluorescence, needed to  comprehend this thesis.
%present some theory behind the TADF process in order to bring the reader into the context and help understand the findings presented in articles.


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\section*{Nenumeruotas poskyriaus pavadinimas, nera turiny}


Several approaches for upconverting non-emissive triplet states to emissive singlet states are known: TADF, hot exciton and triplet-triplet annihilation (TTA) (Figure \ref{fig:upconvert}). 
In case of hot exciton process, the excitons are converted in high-lying (called hot) triplet states (T\tb{n}) whose energy is close to high-lying singlet state (S\tb{n}).......

\begin{figure}[ht]\centering
	\centering\includegraphics[width=8cm]{upconvert.pdf}
	\caption{Multiple ways of harvesting "dark" triplet states.} \label{fig:upconvert}
\end{figure}

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\section*{Nenumeruotas poskyriaus pavadinimas, nera turiny 2}


The TADF, on the other hand, can achieve \SI{100}{\%} internal quantum efficiency (IQE), however small energy difference between lowest lying singlet ($S\sub{1}$) .........($k\sub{rISC}$) can be expressed in a Boltzmann distribution relation: 

\begin{equation}
    k\sub{rISC} = A \exp{- \frac{\Delta E\sub{ST}}{kT}}. \label{eq:risc_boltz}
\end{equation}



Just after the excitation the most planar conformers with fastest radiative decay and bluest emission will emit first, followed by conformers with progressively larger twist angles and therefore redshifted emission. The last of prompt fluorescence will be radiated by most orthogonal conformers. On the other hand, the delayed emission will be promoted by minimized \dEst{} gap of the most twisted conformers producing the initial delayed emission at the long-wavelength end of the spectra. The TADF emission will then be blueshifted as the conformers with larger \dEst{} undergo rISC.
The sum of dispersed \kr{r} and \kr{TADF} rates will produce multiexponential decay transients.




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