Organic semiconductors have attracted considerable attention due to their applications in low-cost (opto)electronic devices. Many successful organic materials utilize blends of several types of molecules that contribute different functions (e.g., serving as donors and acceptors in solar cells). In blends, the local environment, which is inherently heterogeneous, strongly influences the (opto)electronic performance and photostability. We use functionalized fluorinated pentacene (F8 TCHS-Pn) molecules as single-molecule probes of the nanoscale environment in blends containing donor and acceptor molecules incorporated into a polymer (PMMA) matrix. Single F8 TCHS-Pn donor (D) molecules were imaged in PMMA in the presence of functionalized indenofluorene (TIPS-IF) or PCBM acceptor (A) molecules using wide-field fluorescence microscopy at various concentrations. Long-lived dark states attributed to a reversible formation of an endoperoxide (TCHS-EPO) were observed, and the EPO formation and reversal processes, which evolved upon acceptor addition, were quantified. Our study provides a nanoscale-level insight into how the presence of acceptor molecules alters the photophysics of the donor molecules dispersed in the polymer. Kinetics of the F8 TCHS-Pn photo-oxidation reaction and its reversal in such blends are determined by a fine balance of the acceptor-modified morphology (which in our case speeds up the photo-oxidation and slows down its reversal) and singlet oxygen quenching by acceptors (which prevents repeated photo-oxidation/reversal events).

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Organic semiconductors have attracted considerable attention due to their applications in low-cost (opto)electronic devices. The most successful organic materials for applications that rely on charge carrier generation, such as solar cells, utilize blends of several types of molecules. In blends, the local environment strongly influences exciton and charge carrier dynamics. However, relationship between nanoscale features and photophysics is difficult to establish due to the lack of necessary spatial resolution. We use functionalized fluorinated pentacene (Pn) molecule as single molecule probes of intermolecular interactions and of the nanoscale environment in blends containing donor and acceptor molecules. Single Pn donor (D) molecules were imaged in PMMA in the presence of acceptor (A) molecules using wide-field fluorescence microscopy. Two sample configurations were realized: (i) a fixed concentration of Pn donor molecules, with increasing concentration of acceptor molecules (functionalized indenofluorene or PCBM) and (ii) a fixed concentration of acceptor molecules with an increased concentration of the Pn donor. The D-A energy transfer and changes in the donor emission due to those in the acceptor-modified polymer morphology were quantified. The increase in the acceptor concentration was accompanied by enhanced photobleaching and blinking of the Pn donor molecules. To better understand the underlying physics of these processes, we modeled photoexcited electron dynamics using Monte Carlo simulations. The simulated blinking dynamics were then compared to our experimental data, and the changes in the transition rates were related to the changes in the nanoscale environment. Our study provides insight into evolution of nanoscale environment during the formation of bulk heterojunctions.

Right click to open a feedback form in a new tab to let us know how this document benefits you. Effect of molecular side groups and local nanoenvironment on photodegradation and its reversibility,"ABSTRACT Degradation of organic semiconductors in the presence of oxygen is one of the bottlenecks preventing their wide-spread use in optoelectronic devices. The first step towards such degradation in functionalized pentacene (Pn) derivatives is formation of endoperoxide (EPO), which can either revert back to the parent molecule or proceed to molecule decomposition. We present the study of reversibility of EPO formation through probing the photophysical properties of functionalized fluorinated pentacene (Pn-R-F8) derivatives. Experiments are done in solutions and in films both at the single molecule level and in the bulk. In solutions, degradation of optical absorption and its partial recovery after thermolysis were quantified for various derivatives depending on the solvent. At the single molecule level, low concentrations of each type of molecules were imaged in a variety of polymer matrices at 633 nm excitation at room temperature in air using wide-field fluorescence microscopy. Fluorescence time trajectories were collected and statistically analyzed to quantify blinking due to reversible EPO formation depending on the host matrix. To understand the physical changes of the molecular system, a Monte Carlo method was used to create a multi-level simulation, which enabled us to relate the change in the molecular transition rates to the experimentally measured parameters. At the bulk level, photoluminescence decay due to photobleaching and recovery due to EPO reconversion were measured for the same derivatives incorporated into various matrices. These studies provide insight into the synergistic effect of the local nanoenvironment and molecular side groups on the oxygen-related degradation and subsequent recovery which is important for development of organic electronic devices.