Quantifying the Polarization of Exciton Transitions in Double-Walled Nanotubular J-Aggregates

Abstract

A fully consistent model for the exciton band structure of double-walled 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) J-aggregates was developed using reduced linear dichroism (LDr) spectroscopy on flow aligned samples. Chemical oxidation was utilized to “turn off”outer wall optical absorption and produce stable aggregate samples with a simplified absorption profile associated only with the nanotube inner wall. The oxidized aggregates were aligned in a flow cell to collect LDr spectra; these spectra reveal a series of both polarized and isotropic transitions. Four spectral transitions, assigned to be purely parallel or perpendicular to the aggregate long axis, that fit both the experimental LDr and isotropic spectra were used create a model for oxidized J-aggregate excitonic absorption. The LDr spectral study was repeated using pristine J-aggregates, and the spectrum for the full double-walled J-aggregates could be fit using six total transitions: four from the ox...