Mesityl‐Appended 1,4‐Bis(β‐acrylonitrile)‐2,5‐dimethoxybenzene: Blue and Green Fluorescent Crystals from a Soluble Donor–Acceptor Molecular System

Abstract

AbstractBecause acrylonitrile‐phenylene‐based π‐conjugated molecules have highly rigid structures (or low structural flexibility), these molecules have low solubility in various organic solvents, including nonpolar and polar solvents such as hexane, ethanol, and dimethyl sulfoxide. Alkylation or PEGulation strategies are useful approaches for designing highly soluble acrylonitrile‐phenylene compounds, but the number of good solvents is limited. Herein, we report mesityl‐appended 1,4‐bis(β‐acrylonitrile)‐2,5‐dimethoxybenzene including an electron donor–acceptor system. The molecule shows good solubility in various organic solvents, such as hexane, toluene, chloroform, dichloromethane, acetone, ethanol, N,N‐dimethylformamide, acetonitrile, and dimethyl sulfoxide, owing to the appended bulky mesityl groups. Spectroscopic measurements were performed in various solutions. The solvatochromic behaviour was investigated according to the polarity and affinities by absorption and photoluminescence (PL) spectroscopic analyses in various solvents. The acrylonitrile unit in the π‐conjugated structure allows rotation under ambient light. E−Z isomerisation was observed owing to its structural flexibility. This feature gave two fluorescent molecular crystals: blue‐PL Z,Z‐molecular crystal BC (minor material, CCDC 2108373, λem=473 nm) and green‐PL E,E‐molecular crystal GC (major material, CCDC 2108365, λem=508 nm). It is reasonable that the more planar donor–acceptor core structure of the E,E‐crystal shows lower energy fluorescence than the slightly twisted structure of the Z,Z‐crystal.