Photophysics of 9-ethynylanthracene based 'push-pull' molecules

The well-known industrial dye 9,10-bis(phenylethynyl)anthracene and its derivatives have been widely studied in literature and have been functionally employed in various fields due to their rich photophysical properties. Here, we aim to explore the photophysical properties of their mono-substituted analogue. Six 9-phenylethynyl anthracenes were synthesized and the fluorescence emission properties and intramolecular charge transfer (ICT) abilities were compared with regard to various electron donating and withdrawing substituents at the para-position of the phenyl ring. The molecules were divided into two groups according to the absence and presence of ICT character according to the experimental observations, which was supported by theoretical calculations. One compound from each group was chosen to make a white light emitting (WLE) solution in DMSO. This solution was further used to prepare a WLE gel using Poly Vinyl Alcohol as the gelator. This gave an excellent CIE index of (0.31, 0.33). Further, fluorescence anisotropy studies show very good sensitivity of these compounds towards microviscosity of their immediate molecular environment. This property led to check the potential of these molecules in studies involving organized media. For example, N,N-dimethylamino substituted compound could sense the critical micellar concentration (CMC) of the bile salt Sodium deoxycholatein aqueous medium Additionally, the nitro substituted compound shows twisted ICT leading to drastic emission quenching and the hyper-sensitivity towards solvent polarity was used to quantitively sense moisture content in cyclic ether solvents like 1,4-Dioxane and THF using three parameters i.e., emission intensity decrease ratio, emission wavelength and lifetime values