Continuous Making, Stretch Breaking, and Exciton Dynamics of a Red-Emissive Organic Submicrometer-Sized Triangular Pyramid

Abstract

Highly photoluminescent, single-component self-assembly being scalable and sustainable has a profound commercial significance. In this article, the challenges that we address in development of self-assembly of π-conjugated molecules are ─(i) feeble photoluminescence caused by poor molecular orientational ordering and (ii) costly fluorescent monomer owing to lack of an atom/step/energy economical synthetic method. We have discovered that a bright yellow fluorescent xanthene analog capable of instantly forming self-assembly can be synthesized by a home-built coil-in-spiral reactor using an inexpensive precursor, pyrogallol. Stimuli such as temperature (35 °C), acid fumes, and apolar solvent can trigger the formation of red-emissive self-assembly. In solution orientation of about 13 molecules yielding hydrogen-bonded self-assembly has a direct resemblance with a Coulomb-coupled J-aggregate highlighted in the Kasha model. After photoexcitation, the excited state dynamics of the monomer progress via three pathways: (i) relaxation (2 ± 0.3 ps), (ii) solvation (19.5 ± 3 ps), and (iii) decay (2.5 ns). On the other hand, self-assembly exciton evolves via two pathways: (i) relaxation (81 ± 25 ps) and (ii) decay (∼1 ns). In the solid state, the self-assembly retains the submicron-sized trigonal pyramidal structures by layer-by-layer stacking of triangular plates. This self-assembly doped in polymer even exhibits mechanofluorescence. Our study will pave way the use of this photoluminescent self-assembly for improved performance of organic/sustainable electronics and stretchable electronics.