About

R. Bruce Weisman is a Professor of Chemistry and Materials Science and NanoEngineering at Rice University, where he also serves as the Associate Chair for Teaching in the Department of Chemistry. His research group investigates the spectroscopy and photophysics of fullerenes and carbon nanotubes, which are closed nanoscopic structures formed from carbon atoms. His work with fullerenes, such as C60 and C70, involves studying their unusual molecular properties and behaviors following light absorption, utilizing time-resolved absorption and emission methods to explore radiationless decay, photochemical reactions, and energy transfer. Additionally, Weisman’s group has made significant contributions to single-walled carbon nanotube spectroscopy, including the discovery of near-infrared nanotube fluorescence in his lab, and has measured and unraveled the absorption and emission spectra of more than 30 semiconducting nanotube species. His research further extends to elucidating nanotube electronic structures and exploring applications in non-invasive biomedical imaging and analytical nanotechnology.

Research topics

• Chemistry
• Materials science
• Optics
• Nanotechnology
• Biochemistry
• Quantum mechanics
• Condensed matter physics
• Physics
• Neuroscience
• Molecular physics
• Organic chemistry
• Chemical physics
• Chemical engineering
• Photochemistry
• Optoelectronics
• Biophysics

Selected publications

• Near‐Infrared Photochemistry Harnesses Excitons for Selective Guanine Functionalization of Single‐Wall Carbon Nanotubes

  Small · 2026-03-31

  articleSenior authorCorresponding

  ABSTRACT The optical and electronic properties of single‐wall carbon nanotubes (SWCNTs) coated by ssDNA strands can be tailored by covalent bonding of guanine nucleobases in the ssDNA to the nanotube side wall. This reaction is induced by the presence of singlet molecular oxygen, which to date has been generated by irradiation of organic dye sensitizers added to the SWCNT suspension. We demonstrate that this guanine functionalization reaction can proceed without organic sensitizers by resonantly irradiating the nanotubes with near‐infrared (NIR) light. The excited nanotubes transfer energy to ground‐state O 2 to form singlet O 2 , which reacts with guanine nucleobases at the excited nanotube to induce covalent functionalization. The nanotubes thus serve as both sensitizer and reaction substrate. Because functionalization shifts the SWCNT absorption peaks to longer wavelengths, samples drift out of resonance with the irradiation light during irradiation. To compensate, we demonstrate that (6,5) SWCNTs can be more efficiently guanine functionalized using sequential irradiation first at 980 nm and then at 1030 nm. Resonant E 22 excitation is also effective, as shown by using 590 nm irradiation to functionalize (6,4) and (6,5) SWCNTs. This self‐sensitized method yields dye‐free guanine‐functionalized nanotubes and, most significantly, enables selective functionalization of specific SWCNT structures in unsorted samples.

  PublisherDOI

• Guanine Functionalization of Single-Wall Carbon Nanotubes: A Quantum Chemical Study

  ACS Nano · 2025-05-29 · 4 citations

  articleSenior authorCorresponding

  The guanine functionalization reaction uses singlet oxygen to covalently link single-wall carbon nanotubes to guanine bases in ssDNA coatings. This creates shallow but densely spaced exciton traps that modulate nanotube band gaps with energetic and spatial control, giving red-shifted electronic transitions. To better understand guanine functionalization, we used quantum chemical computations to compare the stabilities of several candidate addends in multiple orientations on the nanotube surface. Structures of three possible isomers of guanine peroxide (GPO), the reactive intermediate formed through reaction of 9-methyl guanine with singlet O2, were optimized using the semiempirical PM3 method. To examine effects of nanotube diameter on adduct stability, we then computed the enthalpy changes for bonding of each GPO isomer to a 6 nm segment of (5,4), (6,5), (7,6), and (8,7) single-wall carbon nanotubes (SWCNTs). Six orientations of the addend on the SWCNT surface were considered for each (n,m) species, giving a total of 72 adduct structures. The results showed that for all four SWCNTs, the most energetically stable adduct is the 4,5-GPO isomer bonded in the ortho L–30 orientation. This adduct can be considered to be a derivative of 1,4-dioxane. Subsequent ab initio DFT and TDDFT computations comparing bonding orientations of one guanine addend on a 12 nm long SWCNT segment found that ortho L–30 gives a slightly reduced HOMO–LUMO gap, a moderately localized exciton structure, and a slightly red-shifted E11 optical transition as compared to the pristine SWCNT, in agreement with experiment. We conclude that guanine functionalization of near-armchair SWCNTs leads mainly to 4,5-GPO addends bonded in the ortho L–30 orientation.

  PublisherDOI

• <i>(Invited)</i> a Quantum Chemical Study of Guanine-Functionalized Swcnts

  ECS Meeting Abstracts · 2025-07-11

  articleSenior author

  Among the various chemical reactions that can alter the optical and electronic properties of single-wall carbon nanotubes (SWCNTs), guanine functionalization (GF) holds special interest. In this reaction, SWCNTs coated by ssDNA oligos are exposed to singlet oxygen molecules. A selective reaction then occurs with the guanine bases in the ssDNA, leading to covalent bonding of those bases to the nanotube sidewall. This reaction generates mild exciton traps whose spatial distribution can be tailored by selecting the number and spacing of guanines within the oligo base sequence. Because an exciton may span several of the densely spaced but shallow trap sites, the nanotube’s excitonic band gap can be tuned and spatially modulated through the GF process. A proper understanding of guanine functionalization requires knowledge of the adduct structure and energy. We present here the results of a quantum chemical study that compares the stabilities of multiple candidate addends in multiple orientations on the nanotube surface. The semi-empirical PM3 method was used to optimize structures of three possible isomers of guanine peroxide (GPO), the reactive intermediate formed through reaction of 9-methyl guanine with singlet O 2 . To examine effects of nanotube diameter and curvature, we then computed the enthalpy changes for bonding of the GPO isomers to a 6 nm segment of (5,4), (6,5), (7,6) and (8,7) SWCNTs. Six orientations of the addend on the SWCNT surface were considered for each (n,m) species, giving a total of 72 studied adduct structures. Our results show that for all diameter SWCNTs, the most energetically stable adduct is the 4,5-GPO isomer bonded in either ortho L 30 or ortho L -30 orientation. This adduct can be viewed as a derivative of 1,4-dioxane. Subsequent ab initio DFT computations comparing bonding orientations on a longer SWCNT segment indicate that ortho L 30 and para L -30 give the most reduced band gaps and most localized HOMOs. Finally, we used TDDFT calculations to simulate absorption spectra and compute spectral red-shifts for guanine-functionalized as compared to pristine SWCNTs.

  PublisherDOI

• Complexity in the Photofunctionalization of Single-Wall Carbon Nanotubes with Hypochlorite

  ACS Nano · 2025-01-08 · 9 citations

  articleOpen accessSenior authorCorresponding

  The reaction of aqueous suspensions of single-wall carbon nanotubes (SWCNTs) with UV-excited sodium hypochlorite has previously been reported to be an efficient route for doping nanotubes with oxygen atoms. We have investigated how this reaction system is affected by pH level, dissolved O2 content, and radical scavengers and traps. Products were characterized with near-IR fluorescence, Raman, and XPS spectroscopy. The reaction is greatly accelerated by removal of dissolved O2 and strongly suppressed by TEMPO, a radical trap. Alcohols added as radical scavengers alter the reaction efficiency and the product peak emission wavelengths. Photofunctionalization with 300 nm irradiation is substantially less efficient at pH levels low enough to protonate the OCl– ion to HOCl. We deduce that in mildly treated high pH samples, the main product is sp2 hybridized O-doped adducts formed by reaction of SWCNTs with atomic oxygen in its 3P (ground) level. By contrast, treatment under low pH conditions leads to sp3 hybridized SWCNT adducts formed by the addition of secondary radicals from reactions of •OH and •Cl. There is also evidence for additional photoreactions of product species under stronger irradiation. Researchers using photoexcited hypochlorite for SWCNT functionalization should be alert to the range of products and the sensitivity to reaction conditions in this system.

  PublisherOA PDFDOI

• Molecular Dynamics Insights into the Guanine Functionalization of Single-Wall Carbon Nanotubes

  The Journal of Physical Chemistry B · 2025-06-29 · 1 citations

  articleSenior author

  ssDNA strands and the corresponding distributions of guanine locations prior to reaction. The simulations explored the effects of interstrand interactions, nanotube end effects, solution ionic strength, DNA/SWCNT mass ratio, and SWCNT diameter on conformations and guanine spacings. We analyzed the impacts of such simulation conditions on the spatial distribution of guanine nucleobases along the nanotube axis. Irregularities in those spacings are suggested to cause inhomogeneities in exciton energy landscapes and be a source of spectral broadening in SWCNTs modified by guanine functionalization.

  PublisherDOI

• New Insights into the Guanine Functionalization of ssDNA-Coated SWCNTs

  ECS Meeting Abstracts · 2024-08-09

  articleSenior author

  Single-walled carbon nanotubes (SWCNTs) are a class of nanomaterials that due to their unique physical and chemical properties hold great promise for use in future nanoelectronics, engineered smart materials, and biomedical applications. The discovery of the guanine functionalization reaction 1 that allows for tailored band gap modulation of carbon nanotubes has sparked interest in prospects for new applications and improved photophysical insights. In this work, we build upon knowledge gained by previous studies of guanine functionalization to use this reaction as a tool to better understand the nature of these hybrids. Using sorted samples, we analyze E 11 spectral shapes of band-gap modified SWCNTs to infer single-site exciton perturbations. These results are correlated with Raman spectra to estimate the fraction of guanine sites that become covalently bonded. Further information is obtained from experimental studies of ionic strength dependence and molecular dynamics simulations of ssDNA-wrapped SWCNT structures prior to guanine functionalization. (1) Zheng, Y.; Bachilo, S. M.; Weisman, R. B. Controlled Patterning of Carbon Nanotube Energy Levels by Covalent DNA Functionalization. ACS Nano 2019 . https://doi.org/10.1021/acsnano.9b03488.

  PublisherDOI

• A New Technology for Industrial Strain Mapping Using Single-Wall Carbon Nanotube Sensors

  ECS Meeting Abstracts · 2024-08-09

  article1st authorCorresponding

  Measurements of mechanical strain are widely used in heavy industry to design and test new structures and to ensure the safety of installed infrastructure. However, the few practical methods for strain measurement all have serious limitations. To complement these methods, we have developed a new strain technology, called S 4 for “strain-sensing smart skin,” which uses single-wall carbon nanotubes (SWCNTs) as microscopic sensors. Nanotubes dilutely embedded in a polymer are applied as a thin film to specimen surfaces of interest. Subsequent strains in the specimen are transmitted by load transfer through the film to the nanotubes, inducing axial compression or extension. Those small structural deformations of the SWCNTs alter the semiconducting band gaps in predictable ways, causing proportional shifts in the peak wavelengths of their near-infrared fluorescence emission. Shifts are quantified by optically exciting the specimen surface and spectrally analyzing the resulting fluorescence to deduce strain values at the probed locations. The S 4 method has recently been implemented using hyperspectral imaging. We demonstrate measurements in less than one minute of strain maps containing hundreds of thousands of pixels with 50 microstrain noise levels and 0.2 mm spatial resolution. This technology has promising potential to become a large-scale commercialized application of carbon nanotechnology.

  PublisherDOI

• A Review: Non-Contact and Full-Field Strain Mapping Methods for Experimental Mechanics and Structural Health Monitoring

  Sensors · 2024-10-12 · 18 citations

  reviewOpen access

  Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field.

  PublisherDOI

• (Nanocarbons Division Richard E. Smalley Research Award) Fluorescence of Single-Walled Carbon Nanotubes: From Discovery to Real-World Applications

  ECS Meeting Abstracts · 2024-08-09

  article1st authorCorresponding

  The unique physical and chemical properties of single-walled carbon nanotubes (SWCNTs) continue to inspire extensive research by many basic and applied researchers. One of the most remarkable features of SWCNTs is their variety of pi-electronic structures associated with specific diameters and roll-up angles. Approximately two-thirds of these structural species are semiconducting and display near-infrared photoluminescence (fluorescence) through direct band gap transitions. I will describe the discovery of this SWCNT fluorescence and the assignment of specific spectral features to physical nanotube structures. Several illustrations of using SWCNT emission spectroscopy in research will then be described, including characterizing sample compositions, capturing images and spectra of single nanotubes in physical and biological environments, and guiding covalent tailoring of nanotube excitonic properties. Finally, I will present an update on an emerging technology for industrial strain measurement that uses SWCNTs as strain sensors that report through spectral shifts in their emission spectra.

  PublisherDOI

• Sequence-Dependent Surface Coverage of ssDNA Coatings on Single-Wall Carbon Nanotubes

  The Journal of Physical Chemistry A · 2024-07-09 · 6 citations

  articleSenior authorCorresponding

  A combination of experimental measurements and molecular dynamics (MD) simulations was used to investigate how the surfaces of single-wall carbon nanotubes (SWCNTs) are covered by adsorbed ssDNA oligos with different base compositions and lengths. By analyzing the UV absorption spectra of ssDNA-coated SWCNTs before and after coating displacement by a transparent surfactant, the mass ratios of adsorbed ssDNA to SWCNTs were determined for poly-T, poly-C, GT-containing, and AT-containing ssDNA oligos. Based on the measured mass ratios, it is estimated that an average of 20, 22, 26, or 32 carbon atoms are covered by one adsorbed thymine, cytosine, adenine, or guanine nucleotide, respectively. In addition, the UV spectra revealed electronic interactions of varying strengths between the nucleobase aromatic rings and the nanotube π-systems. Short poly-T DNA oligos show stronger π-π stacking interactions with SWCNT surfaces than do short poly-C DNA oligos, whereas both long poly-C and poly-T DNA oligos show strong interactions. These experiments were complemented by MD computations on simulated systems that were constrained to match the measured ssDNA/SWCNT mass ratios. The surface coverages computed from the MD results varied with oligo composition in a pattern that correlates higher measured yields of nanotube fluorescence with greater surface coverage.

  PublisherDOI

Recent grants

• Quantitative Fluorimetric Analysis of Single-walled Carbon Nanotubes

  NSF · $493k · 2008–2012

• Optical Analysis and Imaging of Single-Walled Carbon Nanotubes

  NSF · $550k · 2011–2015

• Advanced Optical Characterization and Imaging of Single-Walled Carbon Nanotubes

  NSF · $606k · 2014–2018

• Tailoring Single-Walled Carbon Nanotubes with Structure-Selective Photochemistry

  NSF · $500k · 2018–2022

• Novel probes for expanding immunobased detection into the short wave infrared spe

  NIH · $372k · 2012–2015

Frequent coauthors

• Sergei M. Bachilo

  243 shared

• Dmitri Tsyboulski

  Janelia Research Campus

  74 shared

• Laurent Cognet

  Université de Bordeaux

  38 shared

• Saunab Ghosh

  Rice University

  36 shared

• Daniel E. Resasco

  University of Oklahoma

  27 shared

• Anton V. Naumov

  25 shared

• R. E. Smalley

  24 shared

• Satish Nagarajaiah

  Rice University

  23 shared

Labs

• Weisman Research GroupPI

  Analytical Method Development, SWCNT Spectroscopy/Photophysics, SWCNT Bio-imaging Applications, Structural Health Monitoring

Education

• Ph.D., Chemistry

  University of Chicago

  1976

• B.A., Chemistry

  Johns Hopkins University

  1971