About

Ryan Chiechi is an Associate Professor and Undergraduate Research Coordinator in the Department of Chemistry at NC State University. He holds a Ph.D. in Chemistry from the University of California, Los Angeles, obtained in 2009, and a B.S. in Chemistry from the University of Oregon, earned in 2001. His research is centered on organic-materials chemistry, specifically the design, synthesis, and implementation of organic (macro)molecules that mitigate the generation and flow of electricity in thin-films and interfaces. His work involves molecular electronics, self-assembled monolayers, conjugated polymers, unconventional nanofabrication, organic photovoltaics, and thermoelectrics. Chiechi's contributions include advancing the understanding and development of high-performance organic electronic devices, such as ambipolar organic electrochemical transistors, and exploring proton transport in polymers, doping effects in fullerene derivatives, and molecular switches. His research aims to address challenges in energy conversion and electronic materials through innovative organic chemistry approaches.

Research topics

• Materials science
• Optoelectronics
• Nanotechnology
• Physics
• Composite material
• Chemical physics
• Polymer chemistry
• Thermodynamics
• Organic chemistry
• Polymer science
• Chemistry

Selected publications

• High‐Performance Ambipolar Organic Electrochemical Transistors Based on Diketopyrrolopyrrole‐Dialkoxybithiazole Conjugated Polymers for Single‐component Inverters

  Advanced Science · 2026-01-21 · 1 citations

  articleOpen accessCorresponding

  ABSTRACT Single‐component complementary inverters based on ambipolar organic mixed ionic‐electronic conductors (OMIECs) offer promise for simplifying logic circuit design and fabrication. However, the mismatched ambipolar transport properties in OMIECs have hindered the realization of such devices. To address this challenge, we designed two ambipolar OMIECs with high‐spin state: PDPPXO‐2TzC4 (where X = 3, 5). These donor‐acceptor (D‐A) conjugated polymers were synthesized through the copolymerization of diketopyrrolopyrrole (DPP) and dialkoxybithiazole (2Tz) units, incorporating modified ethylene glycol side chains. Both materials demonstrated outstanding and relatively balanced ambipolar OECT performance, achieving an on‐off ratio exceeding 10 5 for both p/n‐type operations. PDPP3O‐2TzC4 achieved normalized maximum transconductances of 0.48 S cm −1 (p‐type) and 0.34 S cm −1 (n‐type), while PDPP5O‐2TzC4 reached 0.42 S cm −1 (p‐type) and 0.29 S cm −1 (n‐type). They also exhibited rapid and well‐matched p‐type and n‐type transient responses, with time constants ( τ on/off ) of less than 5 ms. Furthermore, leveraging the relatively balanced ambipolarity of PDPPXO‐2TzC4, we fabricated functional single‐component complementary inverters and obtained ternary logic characteristics under specific V DD . A biocompatibility assessment using human gingival fibroblasts (HGF) confirmed that PDPPXO‐2TzC4 is suitable for biological applications, laying a foundation for future OECT devices based on these materials in logic circuits and biomedical fields.

  PublisherOA PDFDOI

• Photo‐Modulated Proton Transport in Merocyanine Metastable‐State Photoacid Based Polymers

  Small · 2026-02-25 · 1 citations

  articleOpen access

  We demonstrate here that light can be used to modulate proton transport in polymeric soft materials using a polymerizable molecular photoswitch. To this end, we design a merocyanine metastable-state photoacid, which we use as a building block to prepare a series of light-responsive polymers. We confirm the metastable character of the proposed monomer, and we elucidate its potential energy surface and the energies associated with its photoisomerization using quantum mechanical calculations. Interestingly, we found that when incorporated into a polymeric matrix, a photoacid loading effect impacts its photochromism and induces significant changes to the polymer nanostructure. Light stimulation of the films results in a reversible decrease in conductivity as the merocyanine simultaneously changes its net charge and functions as a photoacid by releasing protons, effecting switching as well as imparting proton conductivity to otherwise insulating polymers. We further exploit the commensurate changes to the polymer nanostructure to fabricate a light-driven hydrogel actuator. Our work establishes a versatile synthetic platform for the design of photo-modulated proton-conductive systems, offering new opportunities for responsive materials and iontronics applications.

  PublisherDOI

• Frontier Orbital Gating of Rectification and Conductance in Tunneling Junctions Comprising Pyridine-Terminated Molecular Wires

  ACS Nanoscience Au · 2025-10-07

  articleOpen accessSenior authorCorresponding

  This work experimentally investigates a mechanism of rectification in molecular junctions proposed by van Dyck and Ratner, supported by theoretical modeling. The defining feature of the mechanism is the spatial separation of frontier molecular orbitals such that each tracks the two leads independently. We achieve this orbital separation in oligophenyleneethylene molecular wires with electron-rich thiols and electron-poor pyridines at their termini. Density functional theory (DFT) calculations show localization of the frontier molecular orbitals at these termini that increases with the molecular length. Measurements of rectification ratios in molecular ensemble junctions using eutectic Ga-In (EGaIn) top-contacts and Au bottom-contacts reveal a length dependence that is almost completely insensitive to the insertion of a nonconjugated methylene spacer between the thiol anchor and conjugated backbone. Simulations using nonequilibrium Green's function + DFT methods show that transport is dominated by the lowest unoccupied molecular orbitals, which track the EGaIn electrode, leading to rectification. These results validate the approach of creating molecular rectifiers by spatially separating the frontier molecular orbitals and show an approach to modeling their behavior under bias in ensemble junctions.

  PublisherDOI

• Substituent effects in a six-state molecular switch

  Physical Chemistry Chemical Physics · 2025-01-01

  articleOpen accessSenior author

  This paper describes a series of four indolinooxazolidine molecular switches capable of accessing multiple distinct states by separately addressing photo- and stereo-isomerism. Photoswitches serve as valuable components in molecular devices owing to their ability to isomerize between distinct states using light as a non-invasive input. While most photoswitches are binary, converting between two states, multistate switches offer expanded operational capabilities and show promise for multi-bit architectures. We synthesized a series of four indolinooxazolidines with varied electronic structure and examined their switching behavior in different solvents. While electron-withdrawing substituents inhibit the photoisomerization pathway, the incorporation of an oligoethylene glycol chain enables both reversible photoisomerisation and acidochromic switching between six combinations of photo- and stereo-isomers.

  PublisherOA PDFDOI

• Photo-modulated proton transport in merocyanine metastable- state photoacid based polymers

  ChemRxiv · 2025-10-29

  articleOpen access

  We demonstrate here that light can be used to modulate proton transport in polymeric soft materials using a polymerizable molecular photoswitch. To this end, we designed a merocyanine metastable-state photoacid, which we used as building block to prepare a series of light-responsive polymers. We confirm the metastable character of the proposed monomer, and we elucidate its potential energy surface and the energies associated with its photoisomerization using quantum mechanical calculations. Interestingly, we found that when incorporated into a polymeric matrix, a photoacid loading effect impacts the photochrome’s photochromism and induces significant changes to the polymer nanostructure. Moreover, we show that the presence of photoacid imparts proton transport properties to an otherwise insulating polymers and we found a clear relationship between the amount of responsive monomer and the material’s proton conductivity. We found that irradiation of polymeric films induces a reversible decrease in conductivity as the photoacid releases protons and undergoes a change in net charge which we demonstrate using a hydrogel actuator. Our study establishes a platform for the design of out-of-equilibrium, photo-modulated proton-conductive materials, offering new opportunities for responsive materials and iontronics applications.

  PublisherOA PDFDOI

• Suppressing parasitic flow in membraneless diffusion-based microfluidic gradient generators

  Lab on a Chip · 2025-01-01

  articleOpen access

  We introduce new microfluidic designs for diffusion-based microfluidic gradient generators. These devices generate highly stable, accurate and convection free gradients by effectively suppressing parasitic flow.

  PublisherOA PDFDOI

• Effect of Regiochemistry on Doping and Thermoelectric Properties of n‐Doped Fullerene Derivatives

  Advanced Electronic Materials · 2025-08-18

  articleOpen access

  Abstract In recent years, fullerene derivatives have been shown to be a promising candidate for n‐type organic thermoelectrics. Adequate tailoring of the solubilizing side chains has proven to be a successful strategy to enhance the performance of these materials. In this work, three different regioisomers of a fullerene derivative are synthesized with two polar diethylene glycol chains. It is shown how small changes in the chemical design alter the assembly properties of the materials, affecting the electronic transport, miscibility with the dopant, and the dielectric properties. It is found that an intermediate crystallinity enables good miscibility, high dielectric constant, and moderate electronic mobility, resulting in a conductivity of 7.7 S cm −1 and a power factor of 35 µW m −1 K −2 , among the highest reported for n‐doped molecular semiconductors.

  PublisherOA PDFDOI

• Author response for "Suppressing parasitic flow in membraneless diffusion-based microfluidic gradient generators"

  2025-02-05

  peer-review
  PublisherDOI

• Self-Assembly Determines Sign of Seebeck Coefficient in Tunneling Junctions Comprising Monolayers and Bilayers of Fullerenes

  Nano Letters · 2024-08-26 · 8 citations

  articleOpen accessSenior authorCorresponding

  We measured the Seebeck coefficient for junctions comprising self-assembled monolayers and bilayers of the fullerene moiety PTEG-1 on Au using eutectic Ga–In in a controlled anhydrous atmosphere by varying the temperature gradient from −12 to 12 °C, observing a linear response in thermovoltage across the range. The sign of the coefficient was positive for monolayers of PTEG-1, (195 ± 8) μV K–1 and negative for bilayers of PTEG-1, (−209 ± 14) μV K–1, indicating a change from HOMO-mediated to LUMO-mediated charge-transport. Charge-transport is nonresonant tunneling for both monolayers and bilayers, but the former self-assembles with the fullerene cage at the chemisorbed interface while the latter includes a fullerene cage at the physisorbed interface, demonstrating that the physical position of the fullerene cage determines the energetic position of the frontier molecular orbitals of PTEG-1.

  PublisherOA PDFDOI

• Carrier–Carrier Repulsion Limits the Conductivity of N‐Doped Organic Semiconductors

  Advanced Materials · 2024-09-09 · 25 citations

  articleOpen access

  Molecular doping is a key strategy to enhance the electrical conductivity of organic semiconductors. Typically, the electrical conductivity shows a maximum value upon increased doping, after which the conductivity decreases. This decrease in conductivity is commonly attributed to unfavorable changes in the morphology. However, in recent simulation work, has shown, that the conductivity-at high doping-is instead limited by electron-electron repulsion rather than by morphology, at least for some material combinations. Based on the simulations, this limitation is expected to show up in the dependence of the Seebeck coefficient versus carrier density: the Seebeck coefficient will follow Heike's formula if carrier-carrier repulsion limits the conductivity. Here, the electrical conductivity and Seebeck coefficient are measured as a function of doping for a series of n-type organic semiconductors. Additionally, the resulting carrier density is measured using metal-insulator-semiconductor diodes, which link dopant loading and the number of charge carriers. At high carrier densities, the Seebeck coefficient indeed follows Heike's formula, confirming that the conductivity is limited by carrier-carrier repulsion rather than by morphological effects. This study shows that current models of hopping transport in organic semiconductors may be incomplete. As a result, this study offers novel insights in the design of organic semiconductors.

  PublisherOA PDFDOI

Frequent coauthors

• Gang Ye

  South China University of Technology

  49 shared

• Xinkai Qiu

  University of Cambridge

  45 shared

• L. Jan Anton Koster

  University of Groningen

  29 shared

• George M. Whitesides

  27 shared

• Jan C. Hummelen

  University of Groningen

  26 shared

• Emily A. Weiss

  Northwestern University

  24 shared

• Jian Liu

  University of Science and Technology of China

  22 shared

• Venda J. Porter

  19 shared

Labs

• Ryan Chiechi LabPI

Education

• PhD, Chemistry and Biochemistry

  University of California Los Angeles

  2005

• Bachelor of Science, Chemistry

  University of Oregon

  2001