Single-component dual emission and full-spectrum color tuning from through-space charge transfer in asymmetric [2.2]paracyclophanes

Abstract

Organic fluorophores are typically limited to a single emission color, because rapid relaxation funnels the excited population to one minimum before it emits. We report asymmetric pseudo-para [2.2]paracyclophanes that break this limit by placing a diphenylaniline donor and a triazine or cyano acceptor on opposite rings of the cyclophane. The rigid transannular contact supports an intramolecular through-space charge-transfer state that is populated alongside the locally excited state, so a single molecule emits from two states at once. Both emissive states here are intramolecular: their combined emission is invariant on dilution to 10−8 M and persists in a rigid polymer matrix. By utilizing solvent polarity to alter the thermodynamic equilibrium between these states, we demonstrate continuous color tuning across the visible spectrum, including the generation of single-molecule white light with CIE coordinates of (0.33, 0.32). Furthermore, we report a negative thermal quenching effect, in which the emission intensity rises rather than falls on heating, achieving photoluminescence quantum yields as high as 88%, a response documented in inorganic phosphors and semiconductors but rare among discrete organic emitters in solution. Translating thermal and dielectric fluctuations into ratiometric spectral readouts positions cyclophanes as a general scaffold for stimuli-responsive optoelectronics.