Tweaking a BODIPY Spherical Self-Assembly to 2D Supramolecular Polymers Facilitates Excited-State Cascade Energy Transfer.

Abstract

Excited state properties such as emission, exciton transport, electron transfer, etc., are strongly dependent on the shape, size and molecular arrangement of chromophore based supramolecular architectures. Herein, we demonstrate creation and control of distinct supramolecular energy landscapes for the reversible control of the excited-state emission processes through cascade energy transfer in chromophore assemblies, facilitated by an unprecedented solvent effect. In methylcyclohexane, a tailor-made Y-shaped BODIPY derivative self-assembles to form an unusual spherical architecture of 400-1200 nm size, which exhibits a single emission at 540 nm upon 475 nm excitation through a normal excitation deactivation process. However, in n-decane, the same BODIPY derivative forms two-dimensional supramolecular sheets, exhibiting multiple emission peaks at 540, 610, 650, 725 and 790 nm with 475 nm excitation due to cascade energy transfer. Further control on the morphology and excitation energy transfer is possible with variable solvent composition and ultrasound stimulation, resulting in enhanced near-infrared emission with an overall pseudo Stokes shift of 7105 cm-1 .