Regiocontrolled Synthesis of Poly[(p-phenylene ethynylene)-alt-(2,5-thienylene ethynylene)]s: Regioregularity Effect on Photoluminescence and Solution Properties

Poly(cyclopentadienylene ethynylene)s: Breaking Conventional Polyenyne Motifs

Conjugated polyenynes comprising dienyne constituents have been synthesized for the first time, expanding the architectural scope of this unique polymer class. The poly(cyclopentadienylene ethynylene)s (PCE)s are soluble in common organic solvents, a rare feature among polyenynes, and possess physicochemical properties that are influenced by the structure of their solubilizing groups. A comparative analysis between the PCEs and other soluble polyenynes, poly(arylene ethynylene)s, and a hybrid of both polymer classes show among other characteristics that the inclusion of cyclopentadienes into the conjugated backbone significantly reduces electronic transition energies while completely suppressing photoluminescence.

METAL-CONTAINING CONJUGATED POLYMERS AS FLUORESCENT CHEMOSENSORS IN THE DETECTION OF TOXICANTS

Fluorescent conjugated polymers have received a great deal of recent interest due to their ability to act as chemosensors to detect various chemical species in both environmental and biological systems with sensitivity and selectivity. Examples from the literature include polymer chemosensors that operate on either fluorescence "turn-on" or "turn-off" as mechanisms of sensor response. These responses can be related to either photoinduced electron transfer or electronic energy transfer mechanisms. Recently, a series of metal-containing polymers or metallopolymers have been explored by various research groups for their use as chemosensors. In many cases, these metallopolymers have been shown to be more sensitive and selective for specific chemical species. This review focuses on fluorescent conjugated polymers as chemosensors, with a specific concentration on recent advances in metallopolymer chemosensors.

Studies of photoinduced electron transfer and energy migration in a conjugated polymer system for fluorescence "turn-on" chemosensor applications

A series of poly[p-(phenyleneethynylene)-alt-(thienyleneethynylene)] (PPETE) polymers with variable percent loadings of the N,N,N'-trimethylethylenediamino group on the polymer backbone were synthesized and fully characterized. Photophysical studies show that changes in the loading of the amino group receptor on the backbone do not affect the polymer electronic structure in either the ground or excited states. The fluorescence quantum yields were found to be directly related to the loading of the amino groups and can be modeled by a Stern-Volmer type relationship. Photophysical studies related the total quenching efficiency to the inherent rate of photoinduced electron transfer (PET), the lifetime of the exciton, the rate of excitation energy migration along the polymer backbone, and the total loading of the receptor on the polymer. The role of the loading dependence on the application of these polymers as fluorescence "turn-on" sensors for toxic metal cations in dilute solution was also studied. Results showed that the fluorescence enhancement upon binding various cations was maintained even when the amino receptor loading along the polymer backbone was reduced.

Rapid Solid-Phase Syntheses of Conjugated Homooligomers and [AB] Alternating Block Cooligomers of Precise Length and Constitution

A new iterative divergent/convergent solid-phase synthesis of precisely defined oligomers is described. The starting monomer is affixed to the solid support so that both ends are free for growth. The polymer-supported n-mer bearing alpha,omega-terminal iodides is divided into two portions. The smaller portion is converted to the polymer-supported (n + 2)-mer by coupling an alpha,omega-dialkyne to the two iodide ends. The larger portion is liberated from the polymer support and then coupled with the polymer-supported portion to form a polymer-supported (3n + 2)-mer with new alpha,omega-terminal iodide end groups. The process is then repeated. The solid-supported material thereby grows in two directions, unlike the common approach of unidirectional growth. This polymer-supported strategy serves as a pseudo high dilution system so that unwanted polymerization does not ensue. Therefore, after each iteration, the oligomer length is more than tripled, making this a rapid growth methodology for precise oligomer syntheses. The methodology is demonstrated by the synthesis of a 17-mer oligo(1,4-phenylene ethynylene) of approximately 120 Å length in seven steps with an overall 20% yield. This solid-supported divergent/convergent tripling protocol is also used for the synthesis of an [AB] alternating block 23-mer containing oligo(1,4-phenylene ethynylene)s and oligo(2,5-thiophene ethynylene)s in an overall 21% yield. The length of the 23-mer is approximately 160 Å.