Fluorescence Enhancement of a Cationic Fluorene–Phenylene Conjugated Polyelectrolyte Induced by Nonionic n-Alkyl Polyoxyethylene Surfactants

Abstract

The modulation of conjugated polyelectrolyte fluorescence response by nonionic surfactants is dependent on the structures of the surfactant and polymer, polymer average molecular weight, and polyelectrolyte-surfactant interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CE) with different alkyl chain lengths (CE with i = 6, 8, 10, and 12) and number of oxyethylene groups (CE with j = 5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide-water 4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains tend to approach as the simulation evolves. However, the minimum distance between the polymer centers of mass increases upon addition of the surfactant and grows with both the surfactant alkyl chain length and the number of oxyethylene groups, although there are no specific polymer-surfactant interactions. A significant increase in the polymer emission intensity has been observed at surfactant concentrations around their critical micelle concentrations (cmcs), which is attributed to polymer aggregate disruption. However, an increase in the solution conductivity for concentrations above the CE cmc has only been observed for the HTMA-PFP/CE system. The enhancement of fluorescence emission intensity and conductivity upon surfactant addition increases with polymer average molecular weights and seems to be controlled by the polymer-surfactant proximity, which is maximum for CE and CE.

Photoluminescence Enhancement of Carbon Dots by Surfactants at Room Temperature

“…The electrostatic attraction between the oppositely charged CDs and surfactants was confirmed by the absence of any change in the PL intensity in the presence of surfactants of the same charge. For non‐ionic surfactants, non‐electrostatic interactions between fluorophores and surfactants could also induce aggregates with enhanced PL emission . Recently, Yang et al.…”

Effects of Charge Density on Photophysics and Aggregation Behavior of Anionic Fluorene-Arylene Conjugated Polyelectrolytes

“…These can be broken up to give a thermodynamically stable solution by adding co-solvents [29], or non-ionic surfactants, such as n -dodecylpentaoxyethylene glycol ether (C 12 E 5 ) [24,26,30,31]. In the case of surfactants, this occurs in the region of the critical micelle concentration (cmc) [24,30,32]. Various factors appear to be involved in the formation and break-up of CPE aggregates [28,29,30,31,33,34], although, as of yet, there is no consensus as to the dominant interaction(s).…”

Anisometric Polyelectrolyte/Mixed Surfactant Nanoassemblies Formed by the Association of Poly(diallyldimethylammonium chloride) with Sodium Dodecyl Sulfate and Dodecyl Maltoside

“…[6][7][8] In addition, the characteristics of polyelectrolyte/surfactant association can be used to understand the interaction between biomacromolecules and surfactants. [9][10][11] Because of the combined hydrophobic and electrostatic driving force of polyelectrolyte/surfactant association, the oppositely charged amphiphile binds onto the polyelectrolyte chains at the critical aggregation concentration (cac) which is well below the critical micelle concentration (cmc) of the pure surfactant. 1,12,13 With increasing surfactant concentration associative phase separation takes place and a solid phase concentrated in the macromolecules and surfactants and a dilute solution are observable.…”