Hanwhuy Lim

NIR-sensitive poly(3,4-ethylenedioxyselenophene) derivatives for transparent photo-thermo-electric converters.

Electrochromism, photothermal effect, and thermoelectric properties of hexyl-derivatized poly(3,4-ethylenedioxyselenophene) are investigated by precisely controlling the morphology. These properties are clearly demonstrated by controlling the applied electrical potential of the polymer films. Especially, the doped polymer film at -0.1 V reveals the highest photothermal conversion efficiency and a power factor of 42.5% and 354.7 μW m(-1) K(-2) , respectively. Efficient visible to near-infrared absorption, photon to heat, and heat to electric conversion has been realized in one film that could benefit in exploiting multifunctional film displays, invisible NIR sensors, photodynamic theragnosis, and thermoelectric devices.

Electrofluorescence switching of fluorescent polymer film

AbstractElectrofluorescence switching has attracted much research attention recently due to its potential applications in the areas of ion sensing, bio analysis, fluorescence imaging, and signaling recognition events. This review describes the chemical structure of electrofluorescent polymers their synthetic strategies, and their patterning characteristics. The designs of these polymers are based on fluorescence quenching through an energy transfer between a fluorophore and an acceptor, which is similar to various types of fluorescence-based sensors. Electrofluorescence devices were designed to demonstrate stable switching processes with different durations while measuring the photophysical properties. The patterning process has shown promise if used to create fluorescent displays, sensors, or for security document applications, but an investigation of patternable polymers and related mechanisms remains for future work.

NIR Electrofluorochromic Properties of Aza-Boron-dipyrromethene Dyes

The photophysical properties of near-infrared (NIR) emissive aza-boron-dipyrromethene (aza-BDP) dyes incorporating nitrofluorene and alkoxy decorations were intensively investigated. Their highly reversible one-electron reduction process showed characteristic electrofluorochromic (EF) properties in the NIR range, depending on the substituents. The nitrofluorene ethynyl-substituted (Type I) dyes showed smaller EF effects than the alkoxy-containing (Type II) dyes because of the difference in their intrinsic fluorescence contrast between the neutral and reduced states (radical anion). In addition, the Type II chromophores showed a larger diffusion coefficient for ion transport, which enhanced the EF contrast and the response time for the fluorescence change at a given step potential. With an optimized condition, the NIR EF ON/OFF ratio reached a value of 6.1 and a long cyclability over 1000 EF cycles between −0.4 V and +0.4 V switching potentials, with approximately 20% loss of the initial ON/OFF switching ratio. The NIR EF switching was visually observed through a visible light cut-off filter, featuring high fluorescence contrast.

Roll type conducting polymer legs for rigid-flexible thermoelectric generator

A roll-type conducting polymer film was explored as a flexible organic p-type thermoelectric leg using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with tosylate. The PEDOT films were prepared through solution casting polymerization and rolled up for a roll-type leg. Due to the high flexibility, the roll-type PEDOT leg enabled easy contact to both top and bottom electrodes. Simulation on the dynamic heat transfer and convective cooling for a vertically roosted rod- and roll-type PEDOT leg showed that the temperature difference (ΔT) between the hot and cold sides of the leg was much higher in the roll than that of the rod. The PEDOT legs were integrated with n-type Bi2Te3 blocks, to give a 36-couple rigid-flexible thermoelectric generator (RF-TEG). The maximum output voltage from the 36-couple RF-TEG under a ΔT of 7.9 K was determined as 36.7 mV along with a high output power of 115 nW. A wearable RF-TEG was prepared upon the combination of the 36-couple RF-TEG with an arm warmer, to afford an output vol...

Multi-color fluorescence switching with electrofluorochromic polymers

The multi-color switching of electrofluorochromism was examined from the thin electrofluorochromic (EF) films of polyfluorene (PFO) and poly(propylenedioxythiophene–phenylene) (P(ProDOT-Ph)). The PFO and P(ProDOT-Ph) films showed vivid blue and yellow fluorescence, respectively, at neutral state but their emission was quenched upon application of oxidation potential leading to ion radical states. The fluorescence from the polymer films was reversibly switched to vivid color when the films were returned to their neutral states. The EF color switching ratio (rc1/c2) between the fluorescent state (c1) and dark (c2) state for the yellow color EF device with P(ProDOT-Ph) film was about four times higher than that of the PFO. Because the two polymer films have different colors and working potentials, a multi-color switching device was fabricated by coating the P(ProDOT-Ph) and PFO films onto working and counter electrodes, respectively. The multi-color EF device showed fluorescence switching from blue (B) to white (W) to yellow (Y), and vice versa, depending on the applied potential. The rc1/c2 for yellow (c1) and blue (c2) switching (Y/B) was larger (9.71) than those for Y/W and W/B. Moreover, the EF switching for Y/B in the multi-EF device was also very effective and showed the largest EF efficiency (EEF = 3.82 × 106) among the EF color switching.

Photothermal actuators based on conjugated polymers (Conference Presentation)

The actuator is implemented based on the conductive polymer layer which causes photothermal conversion through the light in the near infrared region. The photothermally induced heat from conducting polymer can be converted into other type of energy such as mechanical, electrical or chemical energy. Especially, photothermal energy conversion into mechanical energy gives a unique method for reversible change of multi-layered actuator from 2-dimensional to 3-dimensional structure by thermal expansion coefficient mismatch among the layers. Herein we present the effect of the layer composition on the photoactuation and demonstrate a light switchable photothermal sensor.

Photothermal effect in conductive polymer layers for structural conversion into a complex 3D structure (Conference Presentation)

The conversion of photons to heat in the conductive polymer films causes local heating to increase temperature at the light exposed area. The resultant heat can be converted into other type of energy such as electrical, mechanical, or chemical energy. In particular, photothermal effect in conductive polymer layers could be used for structural changes of the 2D structures into a complex three-dimensional (3D) structure. Herein we report the preparation of photothermal conductive polymer layers (CPL) and the integration of CPLs into a 2D structured film, to optimize not only the light-to-heat but also 2D-to-3D structural conversion.

Conjugated polymer thin films for dynamic generation of photothermal patterns (Erratum)

A method of modeling RF properties of single layer guest-host, deoxyribonucleic acid-based biopolymer and polymethylmethacrylate-based, silver nanoparticle composite films, using the transmission matrix method (TMM) is presented. There is excellent correlation between the modeled and experiments results.