Steady-state and Time-resolved Spectroscopic Studies of Benzanilides

Abstract

yV-methylbenzanilide, dissolved in nonpopular and weakly polar solvents at room temperature and at 77 K, shows only two fluorescence modes, i.e., the normal and the charge-transfer emissions at 320 nm and 520 nm, respectively. The fluorescence is deactivated with two decay times, 30 ps and 2.05 ns, in MCH solution.

Substituent Effect on the Dual Fluorescence of Benzanilides and N-Methylbenzanilides in Cyclohexane. Direct Evidence for Intramolecular Charge Transfer

“…The long-wavelength emission of MBA was then suggested to originate from the intramolecular charge transfer (CT) state, whereas that of BA was ascribed to the overlapped emission from a PT state and a CT state 3a. This assignment has been supported by Heldt et al and Lucht et al, but with modified source for the PT state of BA. The new version assumed that the PT state was formed from the intermolecular hydrogen-bonded aggregates formed from the hydrophilic trans -BA in a hydrophobic environment such as in hexane .…”

Photochemistry of para substituted benzanilides in solution: Preparative and mechanistic studies

“…In the case of amides 6 and 8, which bear a carbonyl group and a nitro group, respectively, the intersystem crossing pathway must be considered as a process involved in the physical deactivation pathway estimating a ϕ T value around 0.50 [30][31][32]. Furthermore, when the reaction solvent is a polar solvent such as acetonitrile and methanol it is known that a twisted amide bond (TICT states) excited state is formed from the singlet state of benzanilides (path (b) in Scheme 3) [18][19][20][21][22][23][24][25][26][27]. Then, stabilization of TICT excited state by polar solvents favors the deactivation of such Table 4 Slopes from the linear relationship between ln(k) and Reichardt's solvent parameter (E T (30)) of some 4-substituted benzanilides measured at 254 nm and 310 nm state through k ' d pathway (path (b) in Scheme 3) preventing in part the photochemical reaction as can be judged from the quantum yields in polar solvents (Table 2).…”

“…The photophysical properties of benzanilides have been intensively studied. The dual fluorescence emission in non-polar and polar solvents [18][19][20][21][22][23][24][25][26][27][28][29] was attributed to the population of local excited state (LE) affording a short wavelength emission, while the nature of the state that originates a longer wavelength emission was subject of debate. Kasha and co-workers assigned the blue-green fluorescence emission to the imidol tautomer of benzanilide [30].…”

“…Likewise, the luminescence spectroscopy of p-methylbenzanilide, N-methyl-p-methylbenzanilide, p-nitrobenzanilides and N-benzylbenzanilide in different conditions has also been studied. Steady-state and time-resolved spectroscopy demonstrated that the relative intensities depended on the solvent polarity [23][24][25].…”

“…The trend observed for polar solvents was also observed in benzanilides irradiated with UV light of 310 nm. The photophysical behavior of benzanilides in polar and nonpolar solvents has been extensively studied and it is known that a significant charge separation between the benzamido group (PhCONH-) and the substituents in para position (R-Ph-) occurs favoring a twisted amide bond excited state (TICT states) [18][19][20][21][22][23][24][25][26][27]. Polar solvents promote the stabilization of the TICT excited state, favoring the deactivation of such species through fluorescence emission and radiationless pathways and preventing any photochemical reaction.…”