Nav: Home

Molecular-like photochemistry from semiconductor nanocrystals

January 21, 2016

Researchers from North Carolina State University have demonstrated the transfer of triplet exciton energy from semiconductor nanocrystals to surface-bound molecular acceptors, extending the lifetime of the originally prepared excited state by six orders of magnitude. This finding has implications for fields ranging from solar energy conversion to photochemical synthesis to optoelectronics to light therapy for cancer treatment.

Excitons are the electron/hole pairs formed in semiconductor nanocrystals upon absorption of light, temporarily storing it as chemical energy. In solar cells, for example, the excitons transport energy through the material so that it can be collected and converted into electricity.

In terms of photochemistry, the major drawback to using most semiconductor nanocrystals as photosensitizers lies in their short excited state lifetimes -- typically tens of nanoseconds -- which renders them inadequate to drive photochemical reactions. NC State chemistry professor Felix Castellano, along with postdoc Cedric Mongin and graduate student Sofia Garakyaraghi, wondered if it would be possible to extend the semiconductor nanocrystal excited state lifetime to time scales long enough to perform chemistry.

"The fundamental question was, 'Can we take a nanoparticle excited state with a lifetime of tens of nanoseconds and extend it through sensitization,'" says Castellano. "If we take the original nanocrystal excited state and transfer its energy to a triplet acceptor on the surface of the nanomaterial, then the molecular triplet excited state you create should have a long enough lifetime to promote chemical reactions. This would also suggest that semiconductor nanocrystals exhibit molecular-like behavior."

Castellano's team used cadmium selenide (CdSe) nanocrystals capped with oleic acid, prepared by Prof. Mikhail Zamkov and his graduate student Natalia Razgoniaeva at Bowling Green State University. Some of the oleic acid is then replaced by the molecular triplet acceptor 9-anthacenecarboxylic acid (ACA). When the CdSe nanocrystal bearing ACA is struck with a green laser pulse, the exciton produced in the CdSe is transferred to the ACA, forming a molecular triplet exciton with a millisecond lifetime. This represents a lifetime extension of six orders of magnitude, enabling subsequent chemical reactivity.

"The other benefit is that by translating the exciton away from the nanoparticle surface, instead of involving the nanoparticle itself in the desired chemical reactions, you won't degrade the nanoparticle," says Castellano. "It can keep absorbing light and transferring the energy into the bulk solution."
-end-
The researchers' findings appear in Science. The research was supported by the Air Force Office of Scientific Research (FA9550-13-1-0106) and the U.S. Department of Energy (DE-AC02-06CH11357).

Note to editors: An abstract of the paper follows.

"Direct Observation of Triplet Energy Transfer from Semiconductor Nanocrystals"

Authors: Cedric Mongin, Sofia Garakyaraghi, Felix Castellano, North Carolina State University; Mikhail Zamkov, Natalia Razgoniaeva, Bowling Green State University

Published: Jan. 22, 2016 in Science

Abstract: Triplet excitons are pervasive in both organic and inorganic semiconductors but generally remain confined to the material in which they originate. Here we demonstrate by transient absorption spectroscopy that CdSe semiconductor nanoparticles, selectively excited by green light, engage in interfacial Dexter-like triplet-triplet energy transfer with surface-anchored polyaromatic carboxylic acid acceptors, extending the excited state lifetime by 6 orders-of-magnitude. Net triplet energy transfer also occurs from surface acceptors to freely diffusing molecular solutes, further extending the lifetime while sensitizing singlet oxygen in aerated solution. The successful translation of triplet excitons from semiconductor nanoparticles to bulk solution implies a general paradigm that such materials are effective surrogates for molecular triplets. The nanoparticles could thereby potentially sensitize myriad chemical transformations relevant for fields as diverse as optoelectronics, solar energy conversion, and photobiology.

North Carolina State University

Related Nanoparticle Articles:

Modeling a model nanoparticle
New research from the University of Pittsburgh Swanson School of Engineering introduces the first universal adsorption model that accounts for detailed nanoparticle structural characteristics, metal composition and different adsorbates, making it possible to not only predict adsorption behavior on any metal nanoparticles but screen their stability, as well.
Nanoparticle therapy targets lymph node metastases
Metastasis, in which cancer cells break free from the primary tumor and form tumors at other sites, worsens the prognosis for many cancer patients.
Nanoparticle computing takes a giant step forward
Inspired by how cellular membranes process biological information, we developed a platform for constructing nanoparticle circuits on a supported lipid bilayer.
Nanoparticle breakthrough in the fight against cancer
A recent study, affiliated with South Korea's Ulsan National Institute of Science and Technology (UNIST) has introduced a novel targeted drug delivery system in the fight against cancer.
Ultra-sensitive sensor with gold nanoparticle array
Scientists from the University of Bath (UK) and Northwestern University (USA) have developed a new type of sensor platform using a gold nanoparticle array, which is 100 times more sensitive than current similar sensors.
Illuminating nanoparticle growth with X-rays
Ultrabright X-rays at NSLS-II reveal key details of catalyst growth for more efficient hydrogen fuel cells.
Chemists create new quasicrystal material from nanoparticle building blocks
Brown University researchers have discovered a new type of quasicrystal, a class of materials whose existence was thought to be impossible until the 1980s.
New nanoparticle superstructures made from pyramid-shaped building blocks
In research that may help bridge the divide between the nano and the macro, Brown University chemists have used pyramid-shaped nanoparticles to create what might be the most complex macroscale superstructure ever assembled.
High-resolution imaging of nanoparticle surface structures is now possible
Using scanning tunnelling microscopy (STM), extremely high resolution imaging of the molecule-covered surface structures of silver nanoparticles is possible, even down to the recognition of individual parts of the molecules protecting the surface.
Scientists discover new nanoparticle, dubbed exomeres
A new cellular messenger discovered by Weill Cornell Medicine scientists may help reveal how cancer cells co-opt the body's intercellular delivery service to spread to new locations in the body.
More Nanoparticle News and Nanoparticle Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.