Materials Chemistry Frontiers Blog

Emerging Investigator: Guangxue Feng

Position           Professor Postdoc           2016–2017  National University of Singapore Education        2011–2016  National University of Singapore        Ph.D.                         2007–2011  National University of Singapore        B.Eng. ORCID            0000-0003-4344-3517

Read Guangxue Feng’s Emerging Investigator Series article in Materials Chemistry Frontiers and learn more about him.

	Cationic AIE-active photosensitizers for highly efficient photodynamic eradication of drug-resistant bacteria
	Yuewen Yu,‡ Yubo Liu,‡ Yitao Chen, Jinke Chen, Guangxue Feng * and Ben Zhong Tang *
	A cationization and cyano introduction molecular engineering strategy is reported to develop AIE-active photosensitizers for high-efficiency PDT eradication of drug-resistant bacteria.
	From the themed collection: Frontiers Emerging Investigator Series
	The article was first published on 21 Nov 2022
	Mater. Chem. Front., 2023, Advance Article
	https://doi.org/10.1039/D2QM01043G

My research interests

10 Facts about me

Click to find out our Emerging Investigators and their work

Supramolecular self-assembly can be described as a spontaneous process of association of individual molecules to construct complex and large architectures with distinct features from the corresponding monomers. Encouraged by the natural self-assembly processes, creating new artificial self-assembled systems with desired properties has become a pressing research area of interest. Accordingly, during the last few decades, the scientific community has invested enormous effort in searching and constructing novel self-organized organic architectures with diverse functionalities, which have registered their potential in a wide range of applications, such as biosensing, drug delivery, tissue engineering, organic electronics, catalysis, and others.

During the last few decades, pyrene, a small polyaromatic hydrocarbon, has captured an immense attention to the scientific community as a unique blue emissive fluorophore. Pyrene has been an outstanding choice in organic functional materials because of its superb photophysical characteristics and versatile applications, and the possibility of synthetic modifications on the pyrene core. In comparison to systems that only enable self-assembly, the examples of pyrene-based transient assembly and further disassembly remain elusive in the past literature. Transient assembly is an out-of-equilibrium process which is thermodynamically unstable, and hence it dissociates into monomers via the disassembly process.

In the search of such assembly–disassembly system, the group of Prof. Apurba Lal Koner of the IISER Bhopal, India, in collaboration with Prof. Anup Pramanik at Sidho-Kanho-Birsha University, have developed a new biogenic amine (BA)-induced pyrene-based transient assembly and spontaneous disassembly system to access blue emissive Py-BA conjugated monomers which exhibited solid-state emissive property in addition to lysosomal targeting application (Figure 1).

Figure 1. Representation of reaction-based transient assembly and disassembly and demonstration of solid-state emission and bioimaging application of the monomers.

The group has demonstrated that the nucleophilic reaction between BA and pyrene-anhydride led to form open polar conjugates which created the transiently assembled network driven by strong π–π and multiple H-bonding interactions. The evolution of transient assembly via ground-state pre-association was fully established by a combination of spectroscopic and microscopic techniques in addition to computational study. Addition of BA such as 1,4-DAB in probe solution governed to generate an intense excimer band near 550 nm (yellow emission) in fluorescence spectra which further showed quenching with BA concentration as well as time (Figure 2a–b).

Figure 2. (a) UV-Vis. and (b) fluorescence spectra of Py-DA (5 µM) with increasing concentration of 1,4-DAB (0–50 µM), inset showing the change of O.D. and fluorescence intensity with concentration. (c) representation of temporal intensity changes in excimer and monomer band in CHCl₃. (d) plot of change of I₅₄₅/ I₄₀₅ ratio with time; inset cuvette images showing transformation of fluorescence color from excimer to monomer species.

Moreover, time-dependent quenching of excimer band with concomitant enhancement of monomer emission near 400 nm signified dissociation of yellow-emissive excimer/ aggregation to blue-fluorescent monomers in solution (Figure 2c–d). SEM study for Py-1,4-DAB conjugate unravelled temporal evolution of larger bulk aggregates at initial time which were transformed to interconnected network morphology due to disassembly (Figure 3a–c). Two types of products, i.e., Py-BA monomers and dimer were mainly responsible for demonstrating such assembly–disassembly phenomenon in solution as evident from NMR and mass spectrometry. The blue-emissive monomer conjugates exhibited yellowish-orange emission in solid-state (Figure 3d) which can be highly useful for fabricating light-emitting devices in the future. Interestingly, the newly formed water-soluble selective Py-BA conjugates were found to be of potential significance as lysosome targeting fluorophores (Figure 3e–f). Their lysosomal staining property provided a great advantage to monitor the lysosomal membrane degradation in a time-dependent manner.

Figure 3. (a)–(c) Time-dependent SEM images of Py-1,4-DAB conjugate in CHCl₃ showing morphological change with time. (d) CIE-coordinate of Py-1,4-DAB solid-state emitter; inset shows fluorescence image of thin-film captured upon illuminating at 365 nm. CLSM images of live BHK-21 cells: (e) merge image of Py-Spermine and lysotracker red (f) scatter plot with Pearson’s correlation coefficient 0.96 ± 0.02 (scale bars: 20 µm).

The work represents an intriguing example of harvesting water-soluble fluorophores with multifunctional features from reaction-induced transient assembly–disassembly processes.

Read the full article in Materials Chemistry Frontiers:

Prof. Apurba Lal Koner (Indian Institute of Science Education and Research Bhopal, India)

Apurba Lal Koner is an associate professor in the Department of Chemistry at the Indian Institute of Science Education and Research Bhopal (India). He received his PhD in Chemistry from Jacobs University Bremen (Germany) in 2009. From 2009 to 2012 he did postdoctoral studies at the University of Oxford (UK). Professor Apurba Lal Koner’s research team is working at the interface of chemistry, biology, and emissive materials and their applications in various research domains. He is the author of more than 95 articles of international repute and cited more than 2600 times with an index H = 25.

Web Page link: https://bionanolab.wixsite.com/akoner-iiserb

Emerging Investigator: Jintao Zhang

Position         Professor Postdoc         2013–2015  Case Western Reserve University (USA)                       2012–2013  Nanyang Technological University (Singapore) Education      2008–2012  University of Singapore                      Ph.D. ORCID          0000-0002-1029-3404

Read Jintao Zhang’s Emerging Investigator Series article in Materials Chemistry Frontiers and learn more about him.

	Hollow CoOX nanoparticle-embedded N-doped porous carbon as an efficient oxygen electrocatalyst for rechargeable zinc–air batteries
	Maomao Yang,‡ Siyu Ding,‡ Xinxin Shu, Wei Pan and Jintao Zhang *
	The porous carbon embedded with hollow cobalt oxide nanoparticles was prepared via a spray-drying method followed by carbonization, which endows rechargeable zinc–air batteries with the improved bifunctional catalytic activity.
	From the themed collection: Frontiers Emerging Investigator Series
	The article was first published on 24 Oct 2022
	Mater. Chem. Front., 2022, Advance Article
	https://doi.org/10.1039/D2QM00858K

My research interests

Key words: interface electrochemistry, electrocatalysis, energy conversion and storage

My research interests include the rational design and the synthesis of advanced electrode materials for electrocatalysis, electrochemical energy storage and conversion. Typically, with the fundamental understanding of interface electrochemical reactions in combination with in situ electrochemical methods, model electrode materials are rationally designed for advanced electrocatalysis and energy storage devices, such as carbon dioxide reduction reaction, oxygen reduction and iodine oxidation reactions for advanced rechargeable batteries.

10 Facts about me

Click to find out our Emerging Investigators and their work

When a molecule absorbs light, electrons can be excited to higher energy states. Multiple ways exist for the extra energy to be released, including emitting photons in radiative processes. The competition between radiative and nonradiative relaxation pathways dictates that the faster the process is, the more likely it is to occur. As such, for light emitting devices, the radiative decay needs to be fast to decrease losses in non-radiative relaxation. On the other hand, for light harvesting devices, it is important that the radiation is suppressed. Hence, it is crucial to control the radiative rate to achieve higher efficiency in light emitting or harvesting devices. Besides altering the chemical structures of fluorophores, the design of their dielectric environment provides a straightforward means of altering their fluorescent properties. Control of radiative rate has been thoroughly achieved and understood for inorganic photonic structures, whereas it is less so for organic ones. However, for the future of flexible devices, it is important to explore this effect in polymer structures so that they can be easily integrated in device design. A promising polymer photonic structure is a microcavity formed by two polymer dielectric mirrors sandwiching a very thin layer of fluorescent material as schematized in Fig. 1a. The dielectric mirrors consist of alternating thin layers of materials with high and low refractive index, which form a photonic crystal with high reflectance that can be engineered in the desired spectral range, making them more efficient than metallic ones. Additionally, they are easy to fabricate from solution.

Recently, researchers at the Rely photonics group at the University of Genoa and their collaborators at the National Research Council in Genoa demonstrated radiative rate change in microcavities incorporating an NIR emitting dye (Fig. 1b). The cavities employ dielectric mirrors consisting of the low-index fluorinated polymer Aquivion and a high-index polyvinyl carbazole, which together present the highest dielectric contrast reported so far for polymer mirrors. The samples are almost completely transparent to visible light (Fig. 1c), but strongly reflect light from 750–870 nm (Fig. 1d). This has been designed to reflect the fluorescence of a stable dye of choice. However, there is an allowed microcavity mode that has lower reflectance intensity at 850 nm.

Figure 1. (a) Schematic of the microcavity structure. (b) Structure of the NIR dye used. (c) Photo of an NIR-Reflecting microcavity. (d) Transmittance spectrum of microcavity.

The dielectric mirrors change the density of states available for photons, making it highly intensified at the microcavity mode (red arrow in Fig. 1d at 850 nm), and change the fluorescence intensity and kinetics. A series of references were fabricated in order to compare the effects of the microcavity. Compared to a film of the dye in polyacrylic acid matrix, the fluorescence intensity in the microcavity is nearly completely suppressed except at the cavity mode where it is amplified 15 times as strongly. (Fig. 2a).

Figure 2. Comparison between fluorescence of the dye/polymer film and the microcavity regarding (a) spectral intensity and (b) fluorescence lifetime.

Fluorescence intensity amplification at the microcavity wavelength is a commonly reported phenomenon. On the other hand, change in the fluorescence lifetime is rarely reported. However, it has been observed in this work (Fig. 2b), where lifetime decreased in the cavity compared to the reference film. Further measurements exclude any unintended effects and confirm that indeed the radiative rate does decrease due to cavity effects.

This significant change in the lifetime was achievable thanks to the high refractive index contrast achieved by the researchers. The system is highly promising for future implementation in devices. Further development of structures achieving higher contrast and using sharper emitters is needed to increase the radiative rate in order to improve performance of light emitting devices.

Corresponding author:

Prof. Davide Comoretto
University of Genoa

Davide Comoretto was born in Milano, Italy, in 1963. He graduated with a major in Physics in 1988. In 1993 he obtained a PhD in Chemical Sciences and was then enrolled as Research Scientist at the Department of Chemistry and Industrial Chemistry of the University of Genoa where he is now Full Professor of Industrial Chemistry. During his research activity, he worked at the Institute of Macromolecular Chemistry – CNR (Milan, Italy), the Department of Physics “A. Volta” (University of Pavia, Italy) and at the Institute for Polymers and Organic Solids at the University of California Santa Barbara (USA) in the group chaired by Prof. A. J. Heeger. He is the Team Leader of the Rely Photonics research group focusing on design and fabrication of functional solution-processed photonic crystals and spectroscopy. The main topics are related to emission control, sensing, thermal shielding, engineering and fabrication of metamaterials, light harvesting enhancement in photovoltaics, and photocatalysis.

Website: https://www.rely-photonics.it/people