Evidence of Aggregate Formation for 2,5-Dialkylpoly(p-phenyleneethynylenes) in Solution and Thin Films

Abstract

The absorptive and emissive behavior of four highly fluorescent bisalkyl-substituted poly(p-phenyleneethynylenes) (R = hexyl, dodecyl, 2-(ethyl)hexyl, and 3,5,5-trimethylhexyl) was examined. Aggregate and excimer formation was seen in solution and in the solid state by a combination of absorption and fluorescence spectroscopy in solvent/nonsolvent (chloroform/methanol) mixtures and in thin films. The aggregates were identified by the occurrence of a sharp absorption centered at 440 nm, undetectable in dilute chloroform solution, and a broad emission at 504 nm. The average size of the aggregate formed in chloroform/methanol solvent mixtures must exceed 1.5 μm, as was evidenced in filtering-experiments utilizing a set of membranes with different pore sizes to successively remove smaller aggregates.

Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

“…Although P1-P5 did not exhibit solvatochromic behaviors in homogeneous solutions, solvent effects on the optical properties were further pursued. The addition of methanol to the homogeneous polymer solution is a general method to investigate the aggregation behaviors [29,30]. The emission spectra of the alkyne-linked polymers P4 and P5 were completely different between the solutions and the solid films.…”

Optically and Redox-Active Ferroceneacetylene Polymers and Oligomers

“…[15] Such materials are of interest since the related phenylene-ethynylenes [16] are known to exhibit photoluminescence [17] and nonlinear optical properties. [18] The oligomers and polymers that we described, however, suffer from various disadvantages that are caused mainly by the CH 2 NMe 2 substituent. First, the redox chemistry of compounds derived from FcCH 2 NMe 2 is quite complicated and mostly irreversible because of interfering protonation/deprotonation processes; second, the highly polar nature of the polyamines hinders their purification; and third, the racemic nature of the starting materials yields a complicated mixture of diastereomeric oligomers and polymers.…”

Solvent effects on optical excitations of poly para phenylene ethynylene studied by QM/MM simulations based on many-body Green's functions theory

“…One specific example in which both morphological and electro-optical properties of polymers are purposefully modified is the formation of highly fluorescent conjugated polymer dots for fluorescence imaging in live cells [13]. Less toxicity together with flexibility and biocompatibility make these polydots attractive substitutes for their inorganic counterparts [14,15].…”

“…Among fluorescent polymers, poly para phenylene ethynylenes (poly-PPE) (see the chemical structure in Figure 1) are a class of strongly conjugated polymers with a rigid backbone and absorption and emission of light tunable from the ultraviolet (absorption) to the visible (emission) range [14]. In particular, PPEs can be used as fluorescence sensors because their fluorescence intensity is sensitive to the presence of other co-solutes.…”

“…The goal is to model the optical properties of poly-PPE in complex morphologies, e.g, polydots as observed experimentally [14,16,20] using an approach which allows the analysis of the interplay between morphology and optical excitations. As a first step toward this goal, a quantum-classical QM/MM approach based on a combination of many body Green's functions theory and a polarizable force field is presented is this paper.…”