Peripheral Substitution of Tetraphenyl Porphyrins: Fine-Tuning Self-Assembly for Enhanced Electroluminescence Asterios Charisiadis, [a] Anthi Bagaki, [a] Elisa Fresta, [d] Katharina T. Weber, [b] Georgios Charalambidis, [a] Christina Stangel, [a] Antonios G. Hatzidimitriou, [c] Panagiotis A. Angaridis, [c] Athanassios G. Coutsolelos,* [a] and RubØn D. Costa* [b, d] Introduction Owing to their fascinating and easy-to-modify optical, structur- al, and electrochemical features, porphyrins have been used widely in numerous applications. [1] Representative examples in- clude artificial photosynthesis, [2] liquid crystals, [3] and light-emit- ting devices, [4] while there have also been reports on their use in catalytic systems [5] and sensors. [6] In addition, owing to the well-developed synthetic approaches and easy modification of the porphyrin macrocycle, they have specifically been de- signed to form films based on supramolecular assemblies. The formation of such films has been achieved by using either sol- vent-based deposition techniques, such as spin-coating and doctor-blading, or by preparing functionalized surfaces, which has aroused interest among scientists working on thin-film op- toelectronic devices. [7] An important requirement for most of the aforementioned applications is the spontaneous self-as- sembly of porphyrins. [8] Several research groups have invested significant efforts in fine-tuning the molecular structure of porphyrins to easily form ordered films under different conditions such as at high temperatures, under ambient atmosphere, and at various con- centrations in solution. [9] The most prominent limitation is that tetraaryl-substituted porphyrins are likely to aggregate in mixed-solvent systems [10] or even in homogeneous solutions. [11] The dominant interaction in these cases is p-stacking, but the aggregation behavior can be altered through suitable substitu- tion on the periphery of the porphyrin ring with long alkyl chains. [12] To date, this approach has not been explored in depth. Indeed, the tendency of porphyrins towards disordered aggregation is detrimental in many device applications be- cause of, for example, charge trapping and exciton quen- ching. [4c, 13] In contrast, ordered self-assemblies are favorable with respect to, for example, electrical conductivity and/or photoconductivity. [14] More specifically, aggregation can lead to shorter excited-state lifetimes and partial loss of luminescence, owing to emission self-quenching. [15] As a result, the use of porphyrins in photovoltaic, sensing, and catalytic applications becomes limited. [16] In order to avoid such issues, the development of suitably functionalized porphyrins that form ordered films and/or self- assembled structures, in which their chromophoric centers are isolated both physically and electronically, is fundamental for device applications. Pioneering examples are the set of scat- tered works focused on the fabrication of thin films based on three diphosphonic acid porphyrin derivatives for photoelec- trochemical applications. [17] Some other examples arose from the self-assembly of several meso-substituted tetrapyrrole mac- [a] A. Charisiadis, A. Bagaki, Dr. G. Charalambidis, Dr. C. Stangel, Prof. Dr. A. G. Coutsolelos Laboratory of Bioinorganic Chemistry Department of Chemistry University of Crete, Voutes Campus 70013 Heraklion, Crete (Greece) E-mail : acoutsol@uoc.gr [b] K. T. Weber, Dr. R. D. Costa Department of Chemistry and Pharmacy University of Erlangen-Nürnberg Egerlandstrasse 3, 91058 Erlangen (Germany) [c] Prof. Dr. A. G. Hatzidimitriou, Prof. Dr. P. A. Angaridis Department of Chemistry Aristotle University of Thessaloniki 54124 Thessaloniki (Greece) [d] E. Fresta, Dr. R. D. Costa IMDEA Materials Institute Technogetafe, Erik Kandel 2 28320 Getafe, Madrid (Spain) E-mail : ruben.costa@imdea.org This article is part of the “Optoelectronics” Special Issue. A link to the issue will appear here once it is compiled. This study reports the synthesis of two novel zinc porphyrin families bearing four or eight alkoxy chains at their peripheral phenyl rings, with the length of the alkoxy chains ranging from 2, to 6, and to 12 carbon atoms. All zinc porphyrin deriva- tives were fully characterized with respect to their photophysi- cal and electrochemical features. The zinc porphyrins could be processed into thin films which, depending on the length of the alkoxy chains on the aryl substituents, were found to be either of an ordered or a disordered nature, as it is revealed by spectroscopic and microscopic techniques. The films contain- ing ordered self-assemblies displayed significantly enhanced electrical conductivity compared to the disordered films. This led to remarkable differences regarding their electrolumines- cence response that occurs at lower bias. Furthermore, their lu- minous efficiency was of almost one order of magnitude higher than that of disordered films. ChemPlusChem 2017, 82, 1 – 13  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 & These are not the final page numbers! ÞÞ These are not the final page numbers! ÞÞ Full Papers DOI: 10.1002/cplu.201700416