Research | Mysite

We are synthetic organic chemists, and we create molecules out of pure curiosity to identify new physical properties

Research Theme: π-Conjugated Molecules and Materials: Synthesis, Properties, Molecular Structure, and Applications

Fully Conjugated Indenofluorene Isomers:

Acenes such as pentacenes received much attention for a long time due to their unique physical properties and applications in organic electronic devices. Unfortunately, pentacene is prone to oxidative degradation, therefore the demand for alternative pentacene-like topologies gave birth to the five conjugated indenofluorene (IF) isomers: Indeno[1,2-b]fluorene, Indeno[2,1-a]fluorene, Indeno[2,1-b]fluorene, Indeno[2,1-c]fluorene, and Indeno[1,2-a]fluorene. The IF isomers are formally antiaromatic with two fewer carbons than pentacene, and thus two fewer π-electrons. Among five IFs, electron-accepting indeno[2,1-c]fluorene (Org. Lett. 2013, 15, 1362) is unique due to its potential application in the bulk-heterojunction device (Appl. Phys. Lett. 2014, 105, 043301) including its ability to reduce the HOMO-LUMO energy gap (compared to another pQDM containing [1,2-b]IF). The original synthesis by Prof. Haley (Org. Lett. 2013, 15, 1362) was the only report on the synthesis of [2,1-c]IF by far until another alternative route was published by us in ChemComm.

Fully Conjugated Indacenodifluorene Isomers:

Inspired by the physicochemical properties and optoelectronic applications of IFs, we envisioned exploring higher-order indenofluorenes in the form of fully conjugated cyclopentafluorene-fused IFs which may be termed Indacenodifluorene (IDF) isomers. IDFs are 9-membered polycyclic arenes and may be obtained by the condensation of 6- and 5-membered hydrocarbon rings in an alternating arrangement. IDF family can be classified as two different isomers: 1) s-Indacenodifluorene (s-IDF) and 2) as-Indacenodifluorene (as-IDF). We are actively engaged and particularly interested in the exploration of the many different IDF isomers (including the first s-IDF isomer in J. Am. Chem. Soc. 2016, 138, 1065) with unique structures since these isomers may become potential low band gap (even open shell) molecules and may find applications in optoelectronic devices in future.

Chemistry of Higher Order Zethrene:

Higher order zethrenes usually showed singlet diradical character in the ground state. For the first time, we have shown that substitution plays an important role in tuning the diradical character and HOMO-LUMO gap. Indeed, we have shown that the choice of right substituents completely eliminates diradical character while a low-lying zwitterionic state is easily accessible in the singlet ground state. For more details on synthesis and optoelectronic properties, see our paper published in The Journal of Organic Chemistry.

Antiaromatic indenofluorenes as ambipolar organic semiconductors:

We synthesize molecules for a purpose. It can be either applications in organic optoelectronic devices or understanding their properties (such as anti-aromaticity). For the first time, the charge-transport properties of our antiaromatic indeno[2,1-c]fluorenes were explored. It was found to show good ambipolar charge transport, with a balanced hole and electron mobilities. Moreover, we reported the first push-pull 4npi-indenofluorene in this Organic Materials paper (open access, free to read).

Understanding anti-aromaticity:

The concept of aromaticity is debated, and thus this topic is quite intriguing. We try to understand the concept of aromaticity from a theoretical point of view by giving experimental validation. To do so, we do multi-step synthesis to prepare novel polycyclic arenes and heteroarenes. Some selected papers on the topic of anti-aromaticity of s-indacene, as-indacene, and pentafulvene were published by us in Org. Biomol. Chem., Chem. Commun., Org. Lett. journals.

Synthesis of non-hexagonal nanographene:

Azulene ring defects in graphene or carbon nanotubes can significantly tune the optoelectronic properties in comparison to hexagonal analog. A formal azulene-embedded polycyclic aromatic hydrocarbon was synthesized and fully characterized. The molecule serves as a tribenzo-extended non-alternant example of peri-acenoacene, and the work is published in JOC.