Effect of bulky side groups on photophysical properties and electroluminescent performance of oligo(styryl)benzenes

Trimeric and Tetrameric Cationic Styryl Dyes as Novel Fluorescence and CD Probes for ds-DNA and ds-RNA

“…The absolute fluorescence quantum yields (Φf) gave very different values between 0.57 and 0.04 (Table 1). Previous observations of analogues of tri-and tetra-substituted oligo-and tetra-substituted oligostyryl benzenes show that, in most cases, Φf ranges from moderate to good but are very dependent on the functional group that incorporates the positive charge [21,33], and this is what is observed in this case. Generally, the lowest Φf was found for methyl-pyridylium analogues T3 and F3, while the highest Φf values were obtained for trialkyl-substituted exocyclic nitrogen analogues T2 and F1.…”

“…Detailed analysis of UV-Vis spectra (Figure 1a) revealed a strong impact of the number of substituents on the central aryl, the tetra-substituted analogues generally being red-shifted in comparison to tri-substituted counterparts. This has been previously observed by some of us in analogous derivatives [21,33], and it is because a conjugation is more effective in the tetra derivatives, leading to a reduction in the energy gap between the HOMO and LUMO and thus a red shift of absorption. Also, methyl-and buthylpyridylium analogues (T3, F3, T5, and F5) cause pronounced bathochromic shift of the absorption maximum (Δλ > +30 nm) in comparison with trialkyl-N-quaternarysubstituted compounds T1, T2, T4, F1, F2, and F4.…”

“…These high Stokes shifts have been observed previously and are due to a structural reorganization of the molecule in the excited state, leading to a planarization of one of its branches in the case of the tri-substituted and two branches in the case of the tetra-substituted. This planarization in the excited state leads to an increase in the conjugation of the molecule in the excited state, an energetic stabilization of this state, and a more red-shifted emission of light [ 21 , 33 ]. This feature gives them an additional advantage in terms of possible biological applications of the new probes [ 34 , 35 ].…”

“…This building block can be found among several antiviral, antifungal [ 15 , 16 ], antibacterial [ 17 ], and anticancer medicines [ 18 ] and inhibitors of HIV integrase [ 19 ]. This class of compounds has attracted a lot of interest because of its electroluminescence and photochromic capabilities, which might make them useful in optical devices [ 20 , 21 ] or as sensors [ 22 ] and biosensors [ 23 , 24 , 25 ]. Further, a 4-aminostyryl derivative of 6-methylquinoline showed potential therapeutic and diagnostic characteristics against Alzheimer’s disease [ 26 ].…”