Poly aromatic hydrocarbon (PAH) based molecules are known for their attractive luminescent properties, which make them suitable candidates for a wide veriety of applications in energy storage, charge-transport, catalysis, photovoltaic, molecular electronics, and optoelectronics.1 High molar absorbtivity, high emission intensity in solid state and high efficiency of photo induced electron transfer (PET) rate are some of the desiarable properties in molecular systems, enabling them for above mentioned applications. However, PAH molecules tend to undergo emission quenching in solid state due to aggregation, facilitated by their planar rigid structure. Aggregation induced emission (AIE) and aggregation induced enhanced emission (AIEE) have been the most effective ways to overcome the deleterious effect of aggregation caused quenching (ACQ).2 Generally, ACQ-to-AIE transformation can be accomplished by incorporating rotating (propeller) units, twisted molecular moiety or bulky substituents into planar ACQ molecules to prevent compact co-facial packing. Mechanistically, restriction in motion (RIM), twisted intramolecular charge transfer (TICT), excited state intramolecular proton transfer (ESIPT) and J aggregate formation (JAF) have been identified as pathways for ACQ-to-AIE transformation.3 In the present investigation, three isomeric anthracene derivatives, (E)-2-(2-(anthracen-9-yl)vinyl)benzonitrile, (E)-3-(2-(anthracen-9-yl)vinyl)benzonitrile and (E)-4-(2-(anthracen-9-yl)vinyl)benzonitrile, with donor- π-acceptor (D-π-A) units, were prepared. The primary focus of our research is to study the impact of isomerization on the photophysical properties of such anthreacene based D-π-A fluorophores. We hypothesized that isomerism in such D-π-A fluorophores can tweak their inherent “push-pull” electronic effect which eventually controlls their aggregation behavior, and in turn, the emission proerpties. The hypothesis has been verified as we achieved ACQ-to-AIE modulation for the anthracene based positional isomers.4 Further, we propose that the inherent “push-pull” effect in the system can be utilized for regulating the back electron transfer during bimolecular PET. This is expected to result in a long lived charge transfer state in the photoexcited state. The presentation will provide the mechanistic approaches and experimental details of our strategy along with the future plans.
References (1) J. Mei, N. L. Leung, R. T. Kwok, J. W. Lam, B. Z. Tang, Chem. Rev. 2015, 115, 11718-11940. (2) Y. Hong, J. W. Lam, B. Z. Tang, Chem. Commun. 2009, 4332-4353.
(3) S. Suzuki, S. Sasaki, A. S. Sairi, R. Iwai, B. Z. Tang, G.Konishi, Angew. Chem. 2020, 132, 9940 –9951.
(4) S. Pratihar, A. Bhattacharyya, E. Prasad, J. Photochem. Photobiol. A: Chem. 2020, 112458.