Featured Research

from universities, journals, and other organizations

Materials: Two ways to tame a radical

Date:
April 24, 2013
Source:
The Agency for Science, Technology and Research (A*STAR)
Summary:
Trapping free electrons with polycyclic aromatic molecules creates materials with enhanced optical, electronic and magnetic properties.

Replacing traditional semiconductors with flexible and lightweight organic components has the potential to realize significant cost savings for manufacturers. Recently, a promising class of organic materials known as open-shell polycyclic aromatic hydrocarbons (PAHs) has gained researchers' attention (see image). These molecules consist of interlocked, benzene-like rings and contain unpaired electrons, or 'free-radical' centers. Interactions between the radical centers and aromatic electrons make these compounds extremely responsive to light- and electron-based stimuli. Unfortunately, these same radical electrons can quickly degrade PAH chemical structures, rendering them unusable.

Jishan Wu from the A*STAR Institute of Materials Research and Engineering in Singapore and an international team of co-workers have now devised a new stabilization strategy that promises to make open-shell PAHs even more practical1. Through clever modification of a prototypical compound known as Chichibabin's hydrocarbon, the team has produced two types of PAHs that retain active radical centers for unprecedented amounts of time.

Chichibabin's hydrocarbon has a sextet of aromatic rings that thermodynamically stabilize radical centers. However, it also has a strong chemical affinity for oxygen atoms and tends to polymerize in their presence. To resolve this issue, Wu and co-workers used a process known as benzannulation to add four additional aromatic benzene rings to the PAH framework. They anticipated this design could enhance thermodynamic stability and block kinetic polymerization interactions.

When the researchers chemically excited the tetrabenzo-Chichibabin's hydrocarbon to an open-shell system, they saw that the radical centers remained active for an unusually long time -- two full days -- before returning to the low-energy ground state. Using a combination of high-resolution spectroscopy and theoretical calculations, the team discovered the radical's benzene rings were oriented at right angles to one another, while the ground-state compound had a relatively flat, butterfly-like ring layout. The large energy barrier between these two geometries kept the radical active. "This opens the possibility of accessing each form of the PAH molecule and understanding its physical properties," says Wu.

The researchers also modified the tetrabenzo-Chichibabin's hydrocarbon with aromatic fluorenyl rings that have well-known radical stabilizing effects. In fact, the stabilizing capacity of this compound proved so strong that the open-shell radical became the lowest-energy state, and the molecule remained stable for months under ambient air and light conditions.

Experiments revealed these new open-shell PAHs to have valuable properties including enhanced two-photon absorption, a strong magnetic response and multiple redox states. Wu notes that these findings may lead to the development of better photodynamic therapies and magnetic imaging techniques in the future.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering


Story Source:

The above story is based on materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Materials may be edited for content and length.


Journal Reference:

  1. Zebing Zeng, Young Mo Sung, Nina Bao, Davin Tan, Richmond Lee, José L. Zafra, Byung Sun Lee, Masatoshi Ishida, Jun Ding, Juan T. López Navarrete, Yuan Li, Wangdong Zeng, Dongho Kim, Kuo-Wei Huang, Richard D. Webster, Juan Casado, Jishan Wu. Stable Tetrabenzo-Chichibabin’s Hydrocarbons: Tunable Ground State and Unusual Transition between Their Closed-Shell and Open-Shell Resonance Forms. Journal of the American Chemical Society, 2012; 134 (35): 14513 DOI: 10.1021/ja3050579

Cite This Page:

The Agency for Science, Technology and Research (A*STAR). "Materials: Two ways to tame a radical." ScienceDaily. ScienceDaily, 24 April 2013. <www.sciencedaily.com/releases/2013/04/130424222325.htm>.
The Agency for Science, Technology and Research (A*STAR). (2013, April 24). Materials: Two ways to tame a radical. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2013/04/130424222325.htm
The Agency for Science, Technology and Research (A*STAR). "Materials: Two ways to tame a radical." ScienceDaily. www.sciencedaily.com/releases/2013/04/130424222325.htm (accessed July 29, 2014).

Share This




More Matter & Energy News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Climate Change Could Cost Billions, According To White House

Climate Change Could Cost Billions, According To White House

Newsy (July 29, 2014) — A report from the White House warns not curbing greenhouse gas emissions could cost the U.S. billions. Video provided by Newsy
Powered by NewsLook.com
Stranded Whale Watching Boat Returns to Boston

Stranded Whale Watching Boat Returns to Boston

Reuters - US Online Video (July 29, 2014) — Passengers stuck overnight on a whale watching boat return safely to Boston. Linda So reports. Video provided by Reuters
Powered by NewsLook.com
Baluchistan Mining Eyes an Uncertain Future

Baluchistan Mining Eyes an Uncertain Future

AFP (July 29, 2014) — Coal mining is one of the major industries in Baluchistan but a lack of infrastructure and frequent accidents mean that the area has yet to hit its potential. Duration: 01:58 Video provided by AFP
Powered by NewsLook.com
Easier Nuclear Construction Promises Fall Short

Easier Nuclear Construction Promises Fall Short

AP (July 29, 2014) — The U.S. nuclear industry started building its first new plants using prefabricated Lego-like blocks meant to save time and prevent the cost overruns that crippled the sector decades ago. So far, it's not working. (July 29) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins