Showing papers by "Alex K.-Y. Jen published in 2007"

Hybrid polymer/sol–gel waveguide modulators with exceptionally large electro–optic coefficients

Abstract: Electro–optic (EO) modulators are typically made from inorganic materials such as LiNbO3, but replacing them with organic EO materials, that is, ones with optical properties that change in response to an electric field, could be a promising alternative because they offer large bandwidth, ease of processing and relatively low cost. Here we incorporate a doped, crosslinked organic EO polymer into hybrid polymer/sol–gel waveguide modulator devices with exceptional performance. The half-wave voltages of the resulting Mach–Zehnder (MZ) and phase modulators at 1550 nm are 1 V and 2.5 V, respectively. The unique properties of the sol–gel cladding materials used in the hybrid structure result in a 100% device poling efficiency, leading to respective in-device EO coefficients of 138 pm V–1 and 170 pm V–1 in the MZ and phase modulators. These results are the first to show in-device EO coefficients that are five to six times larger than those of the benchmark inorganic material.

Ultralarge and thermally stable electro-optic activities from supramolecular self-assembled molecular glasses.

Abstract: A series of molecular engineered organic glasses have been prepared to exploit the use of complementary Ar−ArF interactions to improve poling efficiency. These self-organized molecular glasses have also been used as host in the binary chromophore system to further improve the number density of chromophores and r33 values. Ultrahigh r33 values (up to 327 pm/V at the wavelength of 1310 nm) and good temporal stability could be achieved in these materials.

Crosslinkable Hole-Transport Layer on Conducting Polymer for High-Efficiency White Polymer Light-Emitting Diodes

Abstract: Organic and polymer light-emitting diodes (LEDs) have been the subject of intensive investigation in recent years because of their potential as emissive elements for flat-panel displays and white-light sources for general lighting As dualinjection devices, multilayer structures with discrete hole-injection layers (HILs) and/or hole-transport layers (HTLs), light-emitting layers (EMLs), and electron-transport layers (ETLs) are necessary for high efficiency, where these layers can be optimized, respectively, according to their functions [1–3] For LEDs based on small molecules, it is rather straightforward to adopt this multilayer strategy via layer-bylayer vacuum deposition However, for polymer-based LEDs, where solution-based casting or spin-coating is the basic way to form films, it is very challenging to form multilayer structures, because of solvent erosion of previously deposited layers during spin-coating [4] To overcome this problem, a

Large Electro-optic Activity and Enhanced Thermal Stability from Diarylaminophenyl-Containing High-β Nonlinear Optical Chromophores

Abstract: Two series of highly efficient and thermally stable nonlinear optical chromophores based on the (4-diarylamino)phenyl electron donors have been synthesized and systematically investigated A modular approach has been employed to synthesize these electron donors with tunable size, shape, and electron-donating abilities Efficient conjugated bridges were extended from these donors and coupled with very strong CF3−TCF electron acceptors to afford chromophores with very high β values (up to 7077 × 10-30 esu at 1907 μm) These chromophores possess much higher thermal stability (with their onset decomposition temperatures all above 220 °C) than those substituted with (4-dialkylamino)phenyl donors Most importantly, the high molecular hyperpolarizability of these chromophores can be effectively translated into very large electro-optic (E-O) coefficients (r33) in poled polymers through suitable shape engineering Exemplified by the chromophore B4, which has a fluorinated aromatic substituent anchored at its dono

Theory-guided design and synthesis of multichromophore dendrimers: an analysis of the electro-optic effect.

Abstract: Extensive experimental and theoretical study suggests that interchromophore electrostatic interactions are among the most severe impediments to the induction and stability of large electro-optic coefficients in electric-field-poled organic materials. In this report, multichromophore-containing dendritic materials have been investigated as a means to minimize unwanted attenuation of nonlinear optical (electro-optic) activity at high chromophore loading. The dendritic molecular architectures employed were designed to provide optimized molecular scaffolding for electric-field-induced molecular reorientation. Design parameters were based upon past experimental results in conjunction with statistical and quantum mechanical modeling. The electro-optic behavior of these materials was evaluated through experimental and theoretical analysis. Experimental data collected from the dendrimer structures depict a reasonably linear relationship between chromophore number density (N) and electro-optic activity (r33) demon...

Hybrid cross-linkable polymer/sol-gel waveguide modulators with 0.65 V half wave voltage at 1550 nm

Abstract: The authors report on a hybrid cross-linked electro-optic (EO) polymer/sol-gel Mach-Zehnder waveguide modulator with a half wave voltage (Vπ) of 0.65V at 1550nm. The low Vπ was achieved by a design that (1) combines both physical vertical tapers in the sol-gel core and photobleached index tapers in the EO polymer and (2) reduces the thickness of the device to 8μm. These combined physical and index tapers result in improved optical mode confinement in the EO polymer with low adiabatic optical transition loss. The reduced thickness results in a larger field across the EO polymer for the same voltage, enabling a lower Vπ.

Electrooptic Polymer Ring Resonator Modulation up to 165 GHz

Abstract: Modulation is demonstrated at 84, 111, 139, and 165 GHz resonances of a traveling-wave electrooptic polymer ring-resonator-based modulator. The modulation response is characterized throughout the W-band, illustrating the resonant response at 84 and 111 GHz. A traveling-wave analysis that includes the compound effect of microwave loss and optical/microwave velocity mismatch in a ring-resonator-based modulator is presented and shows a good agreement with experimental results. The ring modulator shows superior performance compared to the Mach-Zehnder modulator in the presence of these limitations when both structures have the same equivalent low-frequency Vpi

Two-photon absorbing block copolymer as a nanocarrier for porphyrin: energy transfer and singlet oxygen generation in micellar aqueous solution.

Abstract: A novel amphiphilic water-soluble 2PA-chromophore-containing block copolymer was designed and synthesized. Micelles (nanostructures) were generated in the aqueous solution using the block copolymer and characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM). We demonstrated that hydrophobic porphyrin could be incorporated into aqueous solution with the assistance of micelles. The results from DLS showed that the average diameters are in the range of 59−77 nm. Efficient energy transfer (as high as 96%) from the 2PA chromophore to porphyrin was observed in micellar aqueous solution even though the donor and acceptor were not covalently bonded. Furthermore, the energy transfer contributes to the efficient generation of the singlet oxygen (by a factor of 2.6 at 800 nm) from the porphyrin guest molecules.

High-Efficiency and Color Stable Blue-Light-Emitting Polymers and Devices†

Abstract: Novel fluorene-based blue-light-emitting copolymers with an ultraviolet-blue-light (UV-blue-light) emitting host and a blue-light emitting component, 4-N,N-diphenylaminostilbene (DPS) have been designed and synthesized by using the palladium-catalyzed Suzuki coupling reaction. It was found that both copolymers poly [2,7-(9,9-dioctylfluorene)-alt-1,3-(5-carbazol-phenylene)] (PFCz) DPS1 and PFCz-DPS1-OXD show pure blue-light emission even with only 1 % DPS units because of the efficient energy transfer from the UV-blue-light emitting PFCz segments to the blue-light-emitting DPS units. Moreover, because of the efficient energy transfer/charge trapping in these copolymers, PFCz-DPS1 and PFCz-DPS1-OXD show excellent device performance with a very stable pure blue-light emission. By using a neutral surfactant poly[9,9-bis(6'-(diethanolamino)-hexyl)-fluorene] (PFN-OH) as the electron injection layer, the device based on PFCz-DPS1-OXD5 with the configuration of ITO/PEDOT:PSS/PVK/polymer/PFN-OH/Al showed a maximum quantum efficiency of 2.83 % and a maximum luminous efficiency of 2.50 cd A -1 . Its CIE 1931 chromaticity coordinates of (0.156, 0.080) match very well with the NTSC standard blue pixel coordinates of (0.14, 0.08). These results indicate that this kind of dopant/host copolymer could be a promising candidate for blue-light-emitting polymers with high efficiency, good color purity, and excellent color stability.

Highly efficient diels-alder crosslinkable electro-optic dendrimers for electric-field sensors

Abstract: One of the most challenging tasks encountered in developing highly efficient electro-optic (EO) devices is to find a material system that possesses all desirable properties such as large EO coefficients, good thermal and mechanical stability, and low optical loss. In order to meet this stringent requirement, we have developed a series of crosslinkable EO dendrimers using the standardized AJL8-type chromophore as the center core and the furyl- and anthryl-containing dendrons as the periphery. Upon adding a trismaleimide (TMI) dienophile, these dendrimers could be in-situ crosslinked via the Diels-Alder cycloaddition and efficiently poled under a high electric field. Through this dynamic process, the spatially voided and π-electron-rich surrounding of the chromophore core changes into a dense and more aliphatic network, with the dipolar chromophore embedded and aligned inside. The resultant materials exhibit large EO coefficients (63-99 pm V -1 at 1.31 μm), excellent temporal stability (the original r 33 values remain unchanged at 100 °C for more than 500 h), and blue-shifted near-IR absorption. With these combined desirable properties, a poled EOD2/TMI film could be processed through multiple lithographic and etching steps to fabricate a racetrack-shaped micro-ring resonator. By coupling this ring resonator with a side-polished optical fiber, a novel broadband electric-field sensor with high sensitivity of 100 mV m -1 at 550 MHz was successfully demonstrated.

Hydrophobic Chromophores in Aqueous Micellar Solution Showing Large Two‐Photon Absorption Cross Sections

Abstract: A series of new hydrophobic two-photon absorbing (2PA) chromophores with varied electron-donating groups in quasi-linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two-photon absorption cross-sectional (δ, expressed in GM = 1 × 10–50 cm4 s photon–1 molecule–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)-block-polystyrene (PMAA-b-PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA-b-PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle-containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water-soluble 2PA materials, which have δ values of less than 100 GM.

Two-Photon Absorption in Quadrupolar Bis(acceptor)-Terminated Chromophores with Electron-Rich Bis(heterocycle)vinylene Bridges

Abstract: Two-photon absorption spectra for a range of bis(acceptor)-substituted bis(dibutoxythienyl)ethene and bis(N-hexylpyrrolyl)ethene chromophores have been recorded using Z-scan and white-light-continuum pump−probe techniques. All the chromophores studied show strong near-infrared two-photon absorption with cross sections in the range of 2400−5900 GM (1 GM = 1 × 10-50 cm4 s/photon) at photon wavelengths between 1.0 and 1.3 μm; cross sections as high as 10000 GM can be accessed close to the one-photon absorption edge. Quantum-chemical calculations reproduce the experimentally observed variations of the two-photon properties with the chemical structure.

Ultrafast Spectroscopic Study of Photoinduced Electron Transfer in an Oligo(thienylenevinylene):Fullerene Composite†

Abstract: Photoinduced electron transfer and competing processes have been studied in composites of an oligo(thienylenevinylene) (OTV), comprised of ten dibuthoxyl-thiophene units separated by vinylene units, and a C 60 derivative, [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM), by using femtosecond transient absorption spectroscopy and sub-nanosecond transient photoconductivity. We find that in OTV:PCBM the photoexcitations decay primarily via intrachain relaxation rather than photoinduced electron transfer from OTV to PCBM. The electron-transfer process requires ca. 14 ps; larger by more than two orders of magnitude than the required time observed in conjugated-polymer:C 60 composites, and also larger than the 0.6 ps singlet-state lifetime in OTV. These observations indicate that the quantum efficiency for photoinduced electron transfer in OTV:PCBM is less than 5%.

All-Dielectric Electrooptic Sensor Based on a Polymer Microresonator Coupled Side-Polished Optical Fiber

Abstract: A novel electrooptic (EO) electric field (E-field) sensor based on side-polished fiber coupled with an EO polymer microring resonator is proposed and demonstrated. An EO polymer waveguide with a ring shape is fabricated on the polished flat of an optical fiber. Light in the fiber evanescently couples into the resonator and forms resonant modes for certain wavelengths and produces notches in the output intensity of the fiber. External electric fields change the index of refraction of the ring waveguide and therefore dither its resonant wavelengths. For light of wavelength on the slope of a resonance notch, a change in the output intensity can be detected. The sensor is all dielectric without metal layers to distort the measured E-field. The resonant structure allows the sensor to potentially have much higher sensitivity than other electrooptic sensors based on Mach-Zehnder or polarization modulation. Since electrooptic polymers have higher electrooptic coefficients, lower dielectric constants and faster electrooptic responses than inorganic crystals, higher sensitivity, lower invasiveness, and higher bandwidth of E-field sensing can be expected. This sensor eliminates unreliable fiber-to-waveguide butt coupling as well as the high propagation loss encountered in the long straight EO polymer waveguides of sensors based on Mach-Zehnder structures. By using the fiber itself as the supporting substrate of the ring waveguide, the sensor can have small size and low disturbance to the measured electric field. The concept is demonstrated using AJLS103 EO polymer. A sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system)

Highly Efficient UV−Violet Light-Emitting Polymers Derived from Fluorene and Tetraphenylsilane Derivatives: Molecular Design toward Enhanced Electroluminescent Performance

Abstract: Novel fluorene-based light-emitting polymers (P1−P3) derived form the copolymerization of 9,9-dihexylfluorene or 9,9-spirobifluorene with tetraphenylsilane derivatives were designed and synthesized by palladium-catalyzed Suzuki coupling reaction These copolymers were readily soluble in common organic solvents and exhibited high glass transition temperature (Tg ≥ 157 °C) and thermal stability The results from photophysical studies showed that these copolymers possess a wide band gap (326−330 eV), which endows them with pure UV−violet emission in solid states with high photoluminescence (PL) quantum efficiencies The PL characteristic of these copolymers remained almost unchanged in spite of the modification with tetraphenylsilane or even with the electron-donating alkoxyl substituents The incorporation of bulky 9,9-spirobifluorene units into one of the copolymers (P3) significantly improved the solid-state PL quantum efficiency up to 83% together with a slightly red-shifted emission The LEDs based on

Cross-Conjugated Polymers with Large Two-Photon Absorption Cross-Sections for Metal Ion Sensing

Abstract: The synthesis and metal ion sensing properties of two new cross-conjugated polymers, poly[(9,9-di-n-hexylfluorene-2,7-diyl)-alt-co-(2-(4-(N,N-(dibutylamino)styryl)benzene)-1,4-diyl)] (P1) and poly[(9,9-di-n-hexylfluorene-2,7-diyl)-alt-co-(2,5-bis(4- (N,N-(dibutylamino)styryl)benzene)-1,4-diyl)] (P2) are reported. These two polymers show very different sensing characteristics from those observed for linear conjugated polymers. Upon binding with different metal ions, P1 and P2 show clear intensity changes and large shift of their fluorescence emission peaks. This combined response significantly improves their binding selectivity. Moreover, the donor-π-bridge-donor (D-π-D) conjugated side chain motifs on P2 endow it with efficient two-photon absorbing (2PA) property. This allows it to be used in two-photon laser scanning microscopy and sensing.

A novel benzoxazole-containing poly(N-isopropylacrylamide) copolymer as a multifunctional sensing material

Abstract: We report a novel multifunctional material, poly(N-isopropylacrylamide) (PNIPAAm) containing 2-(2-hydroxyphenyl)benzoxazole (HPBO), for sensing pH, zinc ion concentration, or temperature. By titration with zinc ions, a clear blue-shifted emission with a high quantum efficiency was detected since the zinc complex prevented the nonradiative decay pathways of the HPBO moiety. The fluorescence characteristics of the copolymer were similar at various acidic or neutral conditions. However, a large blue shift on the emission maximum was exhibited under the basic condition, due to the disruption of the ESIPT process by the phenolate anion. The LCST affected the fluorescence properties significantly at the basic condition because the incompatibility between the PNIPAAm chain and phenolated HPBO moieties resulted in aggregation formation. The present study demonstrates that the new benzoxazole-containing PINPAAm copolymer could be potentially used as multifunctional sensing material.

Theoretical and experimental studies on the surface structures of conjugated rod-coil block copolymer brushes

Abstract: A combined theoretical and experimental investigation of conjugated rod−coil block copolymer brushes is reported. The theoretical study for the surface structures of rod−coil block copolymer brushes was established based on the simulation method of dissipative particle dynamics. The effects of solvent stimuli, grafting density, and rod−coil block ratio of the polymer brushes on the surface structures were examined. The rod blocks of polymer brushes were found to be well-dispersed on the surface in their good solvents. On the other hand, aggregative domains of the rod blocks were formed in their poor solvents with the conformations of isolated islands or worm-like structures depending on the grafting density of the polymer brushes. The aggregative domains tend to stay on top of the coil blocks for small rod-to-coil block ratio. However, the submergence of the aggregative domains into the coil blocks is thermodynamically preferred for large enough rod-to-coil block ratio. New multifunctional amphiphilic rod...

Efficient acceptor groups for NLO chromophores: competing inductive and resonance contributions in heterocyclic acceptors derived from 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran

Abstract: The 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) group has been identified as a particularly strong acceptor suitable for the realization of highly efficient second-order NLO chromophores. To provide guidelines for a further improvement of heterocyclic acceptors, we present Sum-Over-States (SOS) calculations of second-order polarizabilities (β) for a series of donor–π-bridge–acceptor (D–π–A) chromophores. In particular, we investigate the effect of replacing the oxygen atom of the furan ring in TCF by a variety of other groups, X (SiH2, CH2, CCH2, NH, CO, S, CCHNO2, SO, and SO2). Overall β is found to increase with the inductive electron-withdrawing character of X, with β being further increased or decreased when X has π-accepting or π-donating character. Within the framework of the two-level model, the effects associated with the π-donating and accepting character can be understood in terms of destabilizing and stabilizing effects on the lowest unoccupied molecular orbitals of the dipolar chromophores. When using the stronger 3-methyl-4-cyano-5-dicyanomethylidene-2-oxo-3-pyrroline (TCP) acceptor and replacing the pyrroline nitrogen atom with the same range of X groups, the inductive electron-withdrawing and π-accepting or π-donating characters of X have the same impact on β as in the TCF motif.

Peptide-mediated surface-immobilized quantum dot hybrid nanoassemblies with controlled photoluminescence

Abstract: Combinatorially selected peptides and peptide–organic conjugates were used as linkers with controlled structural and organizational conformations to attach quantum dots (QDs) at addressable distances from a metal surface. This study demonstrates an approach towards nanophotonics by integrating inorganic, organic, and biological constructs to form hybrid nanoassemblies through template-directed self-assembly. Peptide–organic-linked QD arrays showed stronger fluorescence than peptide-linked QD arrays. We attribute this difference primarily to the increased number density of QDs on peptide–organic-linked QD arrays.

Nanostructured Functional Block Copolymers for Electrooptic Devices

Abstract: Three dendron−linear diblock copolymers with a polyene-type nonlinear optical (NLO) chromophore incorporated in the dendron segment and polystyrene as the linear block were synthesized to investigate the effect of nanostructures on electrooptic (EO) properties. These block copolymers form nanostructures with a periodicity between 36 and 44 nm, which can be characterized using atomic force microscopy (AFM). High EO coefficients (r33) up to 64 pm/V can be achieved in these materials that only have relatively low chromophore concentrations (the highest one is 18 wt %). The resulting poled copolymers also showed good temporal stability. More than 81% of the original r33 value can be retained after being isothermally heated at 85 °C for more than 500 h. On the contrary, the results from the guest−host systems (the chromophore was dispersed into polystyrene) only exhibited lower r33 values and very poor thermal stability (less than 30% of the original r33 values remained after 120 h at 85 °C). These results cle...

Direct surface functionalization of indium tin oxide via electrochemically induced assembly

Abstract: A new methodology has been developed to covalently bond organic functional monolayer on ITO through electrochemically induced assembly of organophosphonic acids. These robust aromatic phosphonates can be deposited on ITO under typical electrochemical conditions at ambient temperature.

Molecular mobility and transitions in complex organic systems studied by shear force microscopy

Abstract: In this paper, we discuss novel nanoscale experimental approaches involving shear forces to investigate inter- and intramolecular mobilities, and their effect on mass and electronic transport, and material deformation properties. We review the non-scanning method of shear modulation force microscopy (SM-FM) used for glass transition analysis, and introduce heated tip atomic force microscopy (HT-AFM) for thermomechanical analysis of material interfaces. The dynamics and kinetics in organic thin films that are typically revealed by the activation energies related to molecular relaxations are determined with intrinsic friction analysis (IFA). Both SM-FM and IFA are applied to optimize the poling efficiency of organic non-linear optical materials involving chromophores, used for photonic devices. They also provide information about intramolecular relaxation properties. A shear force analysis involving HT-AFM was used to investigate the interfacial strength of silica nanoparticles and poly(trimethylsilylpropyne), which are known to form a reverse-selective membrane nanocomposite system.

Plasmon resonant structures with unique topographic characteristics and tunable optical properties for surface-enhanced Raman scattering

Abstract: A simple, inexpensive, parallel approach has been developed for scalable large-area fabrication of two-dimensional (2D) periodic arrays of plasmon resonant structures. This method allows engineering of plasmon modes through precise tailoring of the structural parameters of metal nanostructures for reproducible Raman enhancement.

Assembly of nanomaterials through highly ordered self-assembled Monolayers and peptide-organic hybrid conjugates as templates

Abstract: Synthesis and processing techniques have now been established for obtaining high quality monodisperse nanocrystals of various metallic and semiconducting materials, fullerenes of distinct properties, single- and multi-wall carbon nanotubes, polymeric dendrimers with tailored functionalities, as well as other nanophase constructs. The next key step towards novel applications of nanostructured materials concerns their positioning, arrangement, and connection into functional networks without mutual aggregation. In this review, we highlight the recent progress of using anthracene- and pyrene-based self-assembling molecules with tunable energetic (pi-pi interactions, hydrogen bonding, dipole-dipole interactions) and variable geometries to create stable, highly ordered, and rigid self-assembled monolayer (SAM) templates with adjustable superlattices on crystalline substrates. Based on aromatic SAM templates, stable and highly ordered self-assembled structures of optoelectronically active C60 have been obtained and shown to exhibit desirable electrical and optoelectronic properties, such as nonlinear transporting effect for molecular electronics and efficient photocurrent generation for mimicking photosynthesis in nature. By using genetically engineered polypeptides with surface recognition for specific inorganics, selective integration of nanoparticles onto aromatic SAM templates have also been realized. Through a combination of spatially confined surface chemical reaction and microcontact printing, sub-micron arrays of peptide-organic hybrid conjugates were successfully generated to serve as templates to achieve the patterned assembly of nanoparticles.

Hybrid polymer/sol|[ndash]|gel waveguide modulations with exceptionally large electro|[ndash]|optic coefficients

Abstract: Electro–optic (EO) modulators are typically made from inorganic materials such as LiNbO3, but replacing them with organic EO materials, that is, ones with optical properties that change in response to an electric field, could be a promising alternative because they offer large bandwidth, ease of processing and relatively low cost. Here we incorporate a doped, crosslinked organic EO polymer into hybrid polymer/sol–gel waveguide modulator devices with exceptional performance. The half-wave voltages of the resulting Mach–Zehnder (MZ) and phase modulators at 1550 nm are 1 V and 2.5 V, respectively. The unique properties of the sol–gel cladding materials used in the hybrid structure result in a 100% device poling efficiency, leading to respective in-device EO coefficients of 138 pm V–1 and 170 pm V–1 in the MZ and phase modulators. These results are the first to show in-device EO coefficients that are five to six times larger than those of the benchmark inorganic material.

Controlled assembly of large π-conjugated n-type molecules on Au(111)

Abstract: Controlled assemblies of the n-type 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA) molecule and its derivatives, 5,6,11,12,17,18-hexaazatrinaphthylene-2,8,14-tricarboxylic acid (HATNA–COOH) and 2,8,14-tri(3,4,5-tridodecyloxyphenylaminocarbonyl)-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-den), on Au(111) electrodes have been investigated using electrochemical scanning tunneling microscopy (ECSTM). Orientations of HATNA and HATNA–COOH molecules on Au(111) electrodes can be manipulated with potential modulation and imaged in situ by ECSTM. By increasing the applied electrode potentials, the HATNA and HATNA–COOH molecules were tuned at the solid/liquid interface to orient from parallel to perpendicular to the electrode surface because of dominating adsorbate–adsorbate interactions such as π–π stacking, hydrogen bonding, and weak dipole–dipole interactions and deprotonation of –COOH groups of the HATNA–COOH molecule at higher positive potentials. However, a stable adsorption orientation independent of applied electrode potentials was observed for the tridendron-containing molecule HATNA-den due to strong interactions between the alkyl chains and the Au(111) substrate, and between π-electrons of the aromatic rings and the Au(111) substrate. The ability to orient adsorbates and to change surface structures by controlling the substrate potential is a great boon to those attempting to create designer two-dimensional structures.