Environmental Effect on the Fluorescence Lifetime and Quantum Yield of Single Extended Luminescent Conjugated Polymers

Abstract

To investigate the local environment's effect on the lifetime and quantum yield of extended polymer chains in the absence of intra-and interchain aggregation, short, rodlike polymers of poly(2,5-di-n-octyloxy-1,4-phenylenevinylene) (DO-PPV) were dissolved in chloroform and then embedded in a polystyrene matrix. The fluorescence lifetime was found to increase by 45% in moving from the solution to the matrix form. By using the absorption and emission spectra of the chloroform solution to estimate the radiative and nonradiative rate constants for the polymer in solution, along with calculations based on an exciton model, the corresponding decay rate constants for the polymer embedded in the matrix were obtained. The close agreement between the calculated and experimental values of fluorescent lifetime in the matrix proved the applicability of the exciton model used. On the basis of the model, the average quantum yield of isolated polymers in the matrix was calculated to be a factor of 2 higher than in solutionsan effect arising from a 59% decrease in the nonradiative rate constant and, to a smaller extent, from a 20% increase in the radiative decay rate due to the different dielectric constants of the environments. These results suggest that by extending and isolating single luminescent polymers, high quantum yield devices are possible.

Cyclodextrin Insulation Prevents Static Quenching of Conjugated Polymer Fluorescence at the Single Molecule Level

“…PMMA) possess low fluorescence QY seems to contradict the common belief that dispersing in a solid matrix leads to increased fluorescence QY, in comparison to a pristine film, due to elimination of the interchain interaction. However, to the best of our knowledge, in the experiments where the CP chains were really isolated (low concentration) the fluorescence lifetime was the only indicator of the fluorescence QY 42. Therefore those experiments in principle could not detect static or ultra‐fast quenching, which apparently is the quenching mechanism at this condition.…”

Conformation and Fluorescence Property of Poly(3-hexylthiophene) Isolated Chains Studied by Single Molecule Spectroscopy: Effects of Solvent Quality and Regioregularity

“…It has been shown that the fluorescence lifetime (τ) of a chromophore composed of N repeating units is inversely proportional to the square of the magnitude of its transition dipole moment (μ N ) via τ ∝ 1 false| μ N false| 2 Therefore,τ is inversely proportional to the conjugation length determined by μ N . ,, A previous study of the fluorescence lifetime of MEH-PPV revealed that the lifetime stayed approximately invariant with decreasing molecular weight until the chain became rodlike (10–15 repeating units), after which the lifetime increased with decreasing chain length as a result of the reduction of conjugation length…”

“…Therefore,τ is inversely proportional to the conjugation length determined by μ N . 4,37,38 A previous study of the fluorescence lifetime of MEH-PPV revealed that the lifetime stayed approximately invariant with decreasing molecular weight until the chain became rodlike (10−15 repeating units), after which the lifetime increased with decreasing chain length as a result of the reduction of conjugation length. 4 The fact that rr-P3HT generally exhibits a shorter fluorescence lifetime than ra-P3HT indicates that the regioregular chain possesses a longer conjugation length, which is consistent with the results of PL spectra.…”

Luminescence nanothermometry

“…A luminescent polymer is a large molecule (macromolecule) composed of repeating structural units (usually connected by covalent chemical bonds) that typically shows visible luminescence (500-600 nm) when optically excited by UV radiation. Although luminescent polymers show relatively low luminescence efficiencies (quantum yield values well below 0.4), 46 they are becoming quite popular for luminescence imaging of fluids and biological systems due to their very good solubility in water. In polymers, luminescence is explained in terms of the existence of luminescent monomers within the macromolecule.…”

“…The luminescence intensity of such monomers is affected by a great variety of parameters such as microenvironmental polarity and symmetry, strength as well as the number of chemical bonds in their surroundings. [46][47][48][49][50] As a consequence, any change in the structural properties of the luminescent polymer would cause a large variation in the resulting luminescence intensity.…”