Greek Cross (+) Aggregate

The independent discovery of dye aggregate by Jelley and Scheibe marked the beginning of a spectacular development in the field of aggregate photophysics.1 Subsequent research warranted an exceptional model for defining the exciton interactions in aggregates, proposed by Kasha and Davydov independently, which was later modified by incorporating the short-range excitonic coupling.2-3 Apart from the well-studied H- and J-aggregate, achieving the orthogonally cross-stacked assembly possessing null excitonic interactions remained elusive. The first crystalline evidence for the chromophoric Greek cross (+) assembly exhibiting monomer-like optical properties was reported in 2018.5 The emergent photophysical properties of the crafted Greek cross (+) architectures were explored using both experimental and computational techniques for understanding the aggregate properties beyond Kasha’s model.6-7 The manifestation of selective hole transfer coupling in the edge-to-edge arranged Greek cross (+) perylenediimide (PDI) dimer resulted in ultrafast dissociation of null exciton and evolution of the charge-separated state in a polar solvent, providing a way forward in the fundamental understanding of null aggregates.8 References 1 (a) Jelley, E. E.; Nature, 1936, 138, 1009– 1010; (b) Scheibe, G.; Angew. Chem., 1937, 50, 212– 219; (c) Ramakrishnan, R.; Niyas, M. A.; Lijina, M. P.; Hariharan, M.; Acc. Chem. Res., 2019, 52, 3075−3086. 2 (a) Kasha, M.; Rawls, H. R.; El-Bayoumi, M.; Pure Appl. Chem., 1965, 11, 371–392; (b) Davydov, A. S.; Sov. Phys. Uspekhi; 1964, 7, 145– 178, 3 Hestand, N. J.; Spano, F. C.; J. Chem. Phys. 2015, 143, 244707. 4 Sebastian, E.; Philip, A. M.; Benny, A.; Hariharan, M.; Angew. Chem. Int. Ed., 2018, 57,15696- 15701. 5 Lijina, M. P.; Benny, A.; Ramakrishnan, R.; Nair, N. G.; Hariharan, M.; J. Am. Chem. Soc., 2020, 142, 17393-17402. 7 Benny, A.; Ramakrishnan, R.; Hariharan, M., Chem. Sci., 2021, 12, 5064– 5072. 8 Sebastian, E.; Hariharan, M.; J. Am. Chem. Soc., 2021, 143, 13769–13781; (b) Sebastian, E.; Hariharan, M.; ACS Energy Lett., 2022 , 7, 696−711. Figure 1