A series of poly(arylene ethynylene) (PAE) conjugated polyelectrolytes (CPEs) have been prepared using palladium-mediated (Sonogashira) coupling chemistry. The series consists of five pairs of polymers that share the same poly(arylene ethynylene) backbone. One member of each pair contains anionic sulfonate (R−SO3 -) side groups, whereas the other member contains cationic bis-alkylammonium (R-N+−R-N+−R) side groups. The repeat unit structure of the poly(arylene ethynylene) backbone consists of a bis(alkoxy)phenylene-1,4-ethynylene unit alternating with a second arylene ethynylene moiety, and five different arylenes were used, Ar = 1,4-phenyl, 2,5-pyridyl (Py), 2,5-thienyl (Th), 2,5-(3,4-ethylenedioxy)thienyl (EDOT), and 1,4-benzo[2,1,3]thiodiazole (BDT). The different arylene units induce variation in the HOMO−LUMO band gap across the series of polymers, resulting in a series of materials that display absorption maxima at wavelengths ranging from 400 to 550 nm and fluorescence maxima ranging from 440 to 600 nm. The absorption and fluorescence properties of the CPEs were investigated in methanol, water, and in methanol/water mixtures. The photophysical data suggest that the CPE chains aggregate in water, but in methanol, the polymers are well solvated such that the optical properties are characteristic of the “molecularly dissolved” chains. Stern−Volmer (SV) fluorescence quenching studies were carried out using ionic naphthalene diimides as electron acceptors. The results show that the fluorescence from the CPEs was quenched with very high efficiency (amplified quenching) when the ionic diimide was charged opposite to the charge on the CPE chain. The sensitivity of the Stern−Volmer quenching response varies strongly across the series of CPEs, with the most efficient quenching seen for polymers that display efficient fluorescence when they are aggregated. The relationship between CPE side chain structure, band gap, fluorescence quantum yield, extent of chain aggregation, and fluorescence quenching efficiency is discussed.

We present a sequential molecular dynamics/quantum mechanics (MD/QM) study and steady-state spectroscopy measurements of the nanostar dendrimer (a phenylene-ethynylene dendrimer attached to a ethynylperylene chromophore) to determine the temperature dependence of the electronic absorption process. We studied the nanostar as separate units and performed MD simulations for each chromophore at 10 and 300 K to study the effects of the temperature on the structures. The absorption spectrum of the nanostar, at 10 and 300 K, was computed using an ensemble of 8000 structures for each chromophore. Quantum mechanical (QM) ZINDO/S calculations were performed for each conformation in the ensemble, including 16 excited states for a total of 128 000 excitation energies, and the intensity was scaled linearly with the number of conjugated units. Our calculations and experimental spectra measured for the individual chromophores and the nanostar are in good agreement. We found that for each system, the spectral features are narrow at 10 K because the transitions are localized in wavelength and the absorption energy depends primarily on the length of the chromophore, while at 300 K, the spectra features are quite broad and blue-shifted due to conformational changes on the systems. We explain in detail the effects of temperature and their consequence for the absorption process.

A time-resolved and steady state photophysical study of a family of conjugated polyelectrolytes (CPEs) with variable chain lengths (ranging from 8 to 108 polymer repeat units per chain) is reported. The CPEs investigated are poly(phenylene ethynelene)s substituted with two carboxylate groups per polymer repeat unit to provide water and methanol soluble conjugated polyelectrolytes. Steady state and ultrafast time-resolved fluorescence and anisotropy measurements were performed to explore the role of chain lengths on the energy transfer processes. We find that the CPEs aggregate under almost all conditions, with the degree of aggregation depending on the length of the conjugated polyelectrolyte chains. These CPEs are highly rigid and planar and present a very small loss of anisotropy during their emission lifetime.