Organics emiconductor materials have recently gained momentum due to their non-toxicity,l ow cost, and sustainability.X ylindein is ar emarkably photostable pigment secreted by fungi that grow on decaying wood, and its relativelys trong electronic performance is enabled by p-p stacking and hydrogen-bonding network that promote charget ransport. Herein, femtosecondt ransienta bsorption spectroscopy with an ear-IRp robe was used to unveil ar apid excited-state intramolecular protont ransfer reaction. Conformational motions potentially lead to a conical intersection that quenches fluorescence in the monomeric state. In concentrated solutions, nascent aggregates exhibit af aster excited state lifetime due to excimer formation, confirmed by the excimer!charge-transfer excited-state absorption band of the xylindein thin film, thus limiting its optoelectronic performance. Therefore, extending the xylindein sidechains with branched alkyl groups mayh indert he excimer formation and improve optoelectronic properties of naturally derived materials.

Organic semiconductors are of interest for (opto)electronic applications due to their low cost, solution processability, and tunable properties. Recently, natural product-derived organic pigments attracted attention due to their extraordinary environmental stability and unexpectedly good optoelectronic performance, in spite of only partially conjugated molecular structure. Fungi-derived pigments are a naturally sourced, sustainable class of materials that are largely unexplored as organic semiconductor materials. We present a study of the optical and electronic properties of a fungi-derived pigment xylindein, which is secreted by the wood-staining fungi Chlorociboria aeruginosa , and its blends with poly(methyl methacrylate) (PMMA) and crystalline nanocellulose (CNC). Optical absorption spectra of xylindein revealed the presence of two tautomers whose structures and properties were established using density functional theory. Pronounced pigment aggregation in polar solvents and in films, driven by intermolecular hydrogen bonding, was also observed. The pigment exhibited high photostability, electron mobility up to 0.4 cm 2 /(V s) in amorphous films, and thermally activated charge transport and photoresponse with activation energies of ∼0.3 and 0.2 eV, respectively. The dark and photocurrents in xylindein:PMMA blends were comparable to those in pristine xylindein film, whereas blends with CNC exhibited lower currents due to inhomogeneous distribution of xylindein in the CNC.

Organic semiconductors have attracted increasing attention due to their low cost, solution processability, and tunable properties. Of special interest are molecules with enhanced environmental stability. We have recently reported on the (opto)electronic properties of a remarkably stable, naturally derived pigment xylindein. Here, we establish that one particular aspect of xylindein's molecular structure, namely the presence of hydroxyl (OH) groups, is critical for enabling its enhanced stability and relatively high electron mobility. In particular, we synthesized a methylated derivative of xylindein, dimethylxylindein, where the OH groups are replaced with OCH 3 groups, and compared photophysics and the (opto)electronic properties of dimethylxylindein and xylindein. We reveal the presence of a long-lived excited state in dimethylxylindein, in contrast to xylindein, which has an efficient fast nonradiative pathway to the ground state. This results in significantly reduced photostability of dimethylxylindein as compared to xylindein. The effective electron mobility, obtained from space-charge-limited currents, in amorphous xylindein films was found to be 4 orders of magnitude higher than that in amorphous and crystalline dimethylxylindein films. In contrast, the photosensitivity of dimethylxylindein is about 2 orders of magnitude higher than that of xylindein. The mechanism of charge transport in all films was thermally activated hopping, with the xylindein films characterized by considerably shallower charge traps than dimethylxylindein films, attributed to hydrogen bonding via hydroxyl groups promoting an efficient conductive network in xylindein.

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We present a study of optical and electronic properties of solutions and films based on the fungi-derived pigment xylindein, extracted from decaying wood and processed without and with a simple purification step (“ethanol wash”). The “post-wash” xylindein solutions exhibited considerably lower absorption in the ultraviolet spectral range and dramatically reduced photoluminescence below 600 nm, due to removal of contaminants most likely to be fungal secondary metabolites. The “post-wash” xylindein-based films were characterized by two orders of magnitude higher charge carrier mobilities as compared to “pre-wash” samples. This underlines the importance of minimizing contaminants that disrupt the conductive xylindein network in xylindein-based electronic devices.