Exploring the substituent effect on the fluorescence and chemiluminescence properties of polyphenylimidazoles

Lately, the fluorescent (FL) and chemiluminescent (CL) properties of polyphenylimidazoles have been of interest to our research group.1-4 Compounds such as 2,4,5-triphenyl-1H-imidazoles (TPI) and 1,2,4,5-tetraphenylimidazoles (TEPI) can be conveniently prepared using a single-flask multicomponent approach, by mixing the appropriate benzaldehyde with benzil and ammonia (or aniline) in glacial acetic acid. Recently,1 we have studied the CL decomposition of hydroperoxides and silylperoxides derived from TPI, upon the addition of base. The effect of the substituents in the 2-phenyl ring on the reaction rate constants and CL quantum yields was analyzed and evidence for the generation of a 1,2-dioxetane as a key intermediate was obtained from Hammett linear free energy relationships.1 On another study,5 we have observed that a Hammett relationship with the FL quantum yield of hydroxylated TEPI derivatives (i.e., TEPI-OH) can be used to rationalize the excited state intramolecular proton transfer (ESIPT) within this molecular framework. Moreover, TEPI and TEPI-OH can be used as activators of the CL transformation known as peroxyoxalate system, with emission efficiencies comparable to some polycyclic aromatic hydrocarbons and TPI derivatives.4 In conclusion, polyphenylimidazoles are valuable substrates for many FL and CL studies.
[1] A. Boaro et al. J. Org. Chem. 2021, 86, 6633; [2] R.A. Reis et al. Luminescence 2019, 34, 234; [3] R.B. Orfão Jr. et al. JBCS 2017, 28, 1896; [4] J. Alves et al. PPS 2015, 14, 320; [5] A.G.G.C. Pinto, R.A. Reis, D.U. Melo, A. Boaro, P. Homem-de-Mello, F.H. Bartoloni, under preparation.
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors are grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo and to the Multiuser Central Facilities at UFABC.