Mr. Christian M. Legaspi Profile

Christian M. Legaspi

at Carnegie Mellon Univ

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Publications (3)

Proceedings Article | 26 September 2016 Paper

The role of local environment on the electronic properties of a novel blue-emitting donor-acceptor compound

Christian Legaspi, Regan Stubbs, David Yaron, Linda Peteanu, Abraham Kemboi, Jesse Picker, Eric Fossum

Proceedings Volume 9923, 99231K (2016) https://doi.org/10.1117/12.2238217

KEYWORDS: Organic light emitting diodes, Matrices, Polymers, Solid state electronics, Lawrencium, Chemistry, Molecules, Lens design, Luminescence, Motion models

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Proceedings Article | 20 August 2015 Paper

Modeling electric field-induced quenching in conjugated polymers and oligomers

Christian Legaspi, Linda Peteanu, David Yaron

Proceedings Volume 9549, 95490D (2015) https://doi.org/10.1117/12.2188620

KEYWORDS: Polymers, Excitons, Systems modeling, Quenching (fluorescence), Dielectrics, Organic light emitting diodes, Molecules, Luminescence, Chemistry, Statistical modeling

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The phenomenon of electric field-induced emission quenching is important in organic light-emitting diodes because operating conditions involve large electric fields. Past experimental work on light-emitting polymers and oligomers showed that field-induced quenching (FIQ) efficiencies are higher in non-rigid molecules such as poly(pphenylene vinylene) or PPV, than in similar, more planar molecules. Based on this relationship, we previously proposed that the applied field enhances internal conversion decay channels. Our further studies built on this idea by examining FIQ in PPV oligomers of varying length using computational methods. Calculations performed at the INDO/S-CI level showed the presence of free electron-hole pair (FEHP) states which are stabilized by the uniform external electric field. These FEHP states undergo an avoided crossing with the fluorescent 1B_u bound exciton state at sufficiently high field magnitudes. The magnitude of the electronic coupling between the FEHP and 1B_u state, determined from these avoided crossings, is found to be a function of the field at which these states cross. This function is universal in that it applies to all FEHP states in PPV. This includes FEHP states on different length oligomers and the multiple FEHP states on a given length oligomer. Combining this universal function with simple models for the surrounding dielectric medium and effects of disorder allowed Marcus theory to be used to develop a model of FIQ. The resulting model yields reasonable quantitative agreement with FIQ magnitudes, dependence on oligomer length, and threshold field strengths at which quenching is observed. Here, the universal curve, relating electronic coupling to the field at which the FEHP and 1B_u states cross, is examined for planar, ordered oligomers of polyfluorene and ladder-type poly(p-phenylene). The dependence is similar to PPV, suggesting that this curve is universal not just across states, but also across this family of conjugated polymers. Given that the electronic couplings are similar, the observed differences in FIQ may be attributed to other factors, including especially the reduced degree of structural disorder present for these more rigid systems.

Proceedings Article | 20 August 2015 Paper

Electronic and optical properties of novel carbazole-based donor-acceptor compounds for applications in blue-emitting organic light-emitting diodes

Christian Legaspi, Regan Stubbs, David Yaron, Linda Peteanu, Matthew Sfeir, Abraham Kemboi, Jesse Picker, Eric Fossum

Proceedings Volume 9549, 95491M (2015) https://doi.org/10.1117/12.2188634

KEYWORDS: Organic light emitting diodes, Absorption, Optical properties, Oscillators, Polymers, Luminescence, Quantum efficiency, Dielectrics, Spectroscopy, Absorption spectroscopy

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