Molecular Design Controls the Optical and Liquid Properties of
Alkyl-π Liquid Blends
Author
Mina Fahmya,b, Fengniu Lub, Kazuya Okitac, Kiyoshi Yagic, Takashi Nakanishia,b,*
Affiliation
bFrontier Molecules Group, MANA, NIMS
aDivision of Soft Matter, Graduate School of Life Science, Hokkaido University
cDepartment of Chemistry, Institute of Pure and Applied Sciences, University of Tsukuba
URL
Biography
Mina Fahmy received his B.Sc. in Chemistry (2017) and M.Sc. in Inorganic Chemistry (2022) from Ain Shams University, Egypt. He is currently pursuing a Ph.D. in the NIMS-Hokkaido University Graduate School Program with a MEXT scholarship. His research focuses on functional molecular liquids, molecular interactions, and stimuli-responsive soft materials.
Abstract
Solvent-free alkyl–π molecular liquids have emerged as soft materials that combine fluidity with the ability to control and tune intermolecular interactions and optoelectronic properties.[1,2] However, it remains insufficiently understood how subtle changes in the structural design of substituents’ alkyl chains regulate donor–acceptor interactions and charge-transfer (CT) photophysical properties in these liquids. In this study, two types of alkylated pyrene derivatives (Py1 and Py2) were blended with an alkylated naphthalenediimide (NDI) (Fig. 1) to develop solvent-free D–A blends, Py1–NDI and Py2–NDI. Although these two blends exhibit comparable properties as bulk liquids, they show marked differences in their optical responses. While Py1–NDI displays CT emission accompanied by a significant red shift, Py2–NDI shows minimal CT contribution and primarily retains the blue emission characteristic of Py2. We propose that the NIR emission in Py1–NDI originates from a cascaded energy-transfer process. Upon UV excitation, Py1 first forms an excimer. Subsequently, the excimer then transfers energy to the Py1–NDI CT state, thereby generating NIR emission from the excited state of the CT complex. In contrast, the Py2–NDI blend suppresses the CT state, resulting in predominantly pyrene emission with only weak NIR emission. MD simulations revealed the characteristic cluster structures and stability of the Py–NDI, highlighting the role played by substituent alkyl side-chain design in the formation of CT complexes in the liquid state.
References
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