Organic co-crystals as a novel approach toward room temperature phosphorescence from organic materials

Room temperature phosphorescence emission from purely organic materials is very rare. The search for phosphorescent organic solid compounds has recently emerged [1], due to their potential application in several fields, ranging from organic electronics to biological sensing, thanks to their reduced toxicity as metal-free substances and their low cost. A turning point in this direction has come from crystal engineering, with the design of solid structures based on the co-crystallization of organic dyes and halogenated co-formers. The key point is the formation, in the solid structure, of halogen bonds between suitable co-formers and electron-rich substituents of the organic components or their ? systems. We recently explored this approach by studying materials obtained by co-crystallization of different organic molecules (e.g. 1,8-naphthalimide derivatives, diphenylacetylene, trans-stilbene) with the co-former 1,4-diiodotetrafluorobenzene [2,3]. The luminescence properties of the solid materials have been analyzed by means of steady-state and time resolved spectroscopic techniques. The results will be here discussed, addressing the role of co-crystallization stoichiometry on the phosphorescence vs fluorescence output from the solid materials. References [1] O. Bolton, K .Lee, H.-J. Kim, K. Y. Lin, J. Kim, Nat. Chem. 3 (2011) 205-210. [2] B. Ventura, A. Bertocco, D. Braga, L. Catalano, S. d'Agostino, F. Grepioni, P. Taddei, J. Phys. Chem. C 118 (2014), 18646-18658. [3] S. d'Agostino, F. Grepioni, D. Braga, B. Ventura, Cryst. Growth Des. 15 (2015), 2039-2045. Acknowledgements Alessio Bertocco and Luca Catalano (Politecnico di Milano, Italy) are gratefully acknowledged. This work was supported by University of Bologna, CNR (Project "PHEEL"), MIUR-CNR project "Nanomax" N-CHEM, and CNR-ASRT (Egypt) Bilateral Cooperation Project "FLUO-NanoFAB".