Zahid N Idayu, Mahmood Mohamad Syafie, Subramanian Balamurugan, Mohd Said Suhana, Abou-Zied Osama K
Department of Chemistry, Faculty of Science, Sultan Qaboos University , P.O. Box 36, Postal Code 123, Muscat, Sultanate of Oman.
Centre for Fundamental and Frontier Sciences in Nanostructure Self-Assembly, Department of Chemistry, Faculty of Science, University of Malaya , 50603 Kuala Lumpur, Malaysia.
J Phys Chem Lett. 2017 Nov 16;8(22):5603-5608. doi: 10.1021/acs.jpclett.7b02601. Epub 2017 Nov 3.
Fluorescence upconversion and transient absorption techniques are used to explain the source of the intense red/near-infrared emission of crystalline 4-dimethylamino-2'-hydroxychalcone. We found that the initially excited enol form undergoes tautomerization in 3 ps to form the keto tautomer. The latter is stable in the ground state as a consequence of J-type aggregation in the crystal packing and is manifested in an absorption peak at 550 nm that spectrally overlaps with the short-lived enol emission, leading to self-reabsorption and adding a factor to the complete depletion of the enol emission. Relaxation of the keto tautomer takes place in the form of intense fluorescence (600-750 nm) with 1.7 ns lifetime. The different spectroscopy in solution is due to vibrational cooling (300 fs), followed by solvation dynamics (5 ps in methanol) and twisting of the hydroxyphenyl ring (16 ps), before relaxation of the enol tautomer in the form of weak green fluorescence with 350 ps lifetime.
