Photophysics of Poly[p-(2,5-didodecylphenylene)ethynylene] in Thin Films

Abstract

The optical properties of thin films of poly[p-(2,5-didodecylphenylene)ethynylene] (DPPE) have been investigated. In chloroform solution the DPPE exhibit structured blue emission with a lifetime of 0.4 ns. In contrast to the solution, pristine DPPE films show a broad featureless green fluorescence with a nonexponential decay with time constants of 1.15 ns (8%) and 5.9 ns (92%). Upon annealing, the emission spectrum returns to a structured blue emission similar to the solution, and the fluorescence decay is nonexponential with a component at 0.45 ns (38%) and 90 ps (62%). Both spin-cast and annealed films possess similar absorption spectra, suggesting that the lifetime difference is due to an excimer-like state in the pristine film and efficient fluorescence from isolated chains within the annealed films. The decrease of the fluorescence lifetime from 0.4 ns (DPPE in solution) to 90 ps (annealed DPPE films) is further attributed to the lack of conformational disorder found within the ordered solid state.

Multicolor Conjugated Polymer Dots for Biological Fluorescence Imaging

“…PPE dots display complex fluorescence decay kinetics, the 440 nm emission peak shows a single exponential decay with time constant of 242 ps, while the 480 nm emission exhibits a bi-exponential decay with time constants of 276 ps and 1.56 ns. This observation is similar to previously observed fluorescence decay kinetics of PPE thin films, which are characterized as a heterogeneous system containing ordered and disordered polymer chains 23. The fluorescence radiative rate constant k R and non-radiative rate constant k NR were estimated by combining the quantum yield [ ϕ = k R /( k R + k NR ] and fluorescence lifetime results [ τ = ( k R + k NR ) -1 ].…”

Poly(p‐phenylene ethynylene)s with Facially Amphiphilic Pendant Groups: Solvatochromism and Supramolecular Assemblies

“…The aggregation of cholate units induced by the presence of water or cyclohexane could lead to a more planar conformation of the PPE backbone, which should be the most probable reason for the observed solvatochromism. [16] With the increase of water content, it is interesting to note that the transparent blue fluorescent solution of P1 in dioxane changes to a yellowish green cloudy liquid, which exhibits scattering of daylight (Tyndall effect, characteristic of nontrue solutions; see Figure 3). The optoelectronic features of conductive polymers are strictly related to their aggregation states and strongly depend on the microstructural environment; therefore, the dramatic difference in UV/Vis absorption should be a reflection of different aggregate states of the polymers in solution.…”

Poly(aryleneethynylene)s

“…One can see that the absorption spectrum sharpens, but that the absorption band centered at 449 nm is unchanged after annealing, while the fluorescence changes from 540 nm (broad, t ¼ 5.9 ns excimeric emission) to 455 nm (t ¼ 75 ps) we think originates from single chains. [78] Spin cast films of 3b display almost no molecular order according to polarization NSOM (Figure 11), while annealed films do show a significant amount of order on the range of microscale domains. One can also look at the temperature dependent thin film absorption spectra of a didodecyl-co-dihexyl-PPE (Figure 12).…”