Time evolution of the solvated and conformationally relaxed emissive excited state of the anionic form of salophen, a Schiff base

Interplay of conformational relaxation and hydrogen bond dynamics in the excited states of fluorescent Schiff base anions

“…2a). This observation can be explained in light of hindrance to the segmental motion and consequently, conformational relaxation at higher viscosity 32–34 and is in line with the larger ϕ f values observed in glycerol. However, viscosity is not the sole factor that determines the excited state dynamics, as is borne out by a distinctly slower fluorescence decay of salampy − in ACN (Fig.…”

“…The neutral Schiff bases typically have t f values of tens of picoseconds and the complexes have lifetimes in the nanosecond regime, unless p-stacking is at play. The anions typically have fluorescence lifetimes of 800-900 ps in methanolic solutions [32][33][34] and their emission spectra exhibit a time dependent fluorescence Stokes shift (TDFSS) over timescales comparable to the solvation times reported earlier. 36 This observation is in line with an earlier report on a Schiff base anion.…”

“…55 The steady state spectra of salampy À , HBAP 2À and salophen 2À in methanol (MeOH) has been recorded afresh to reproduce our recent reports. [33][34][35] Steady state spectra thus indicate the dependence of the excited state phenomena in the Schiff base anions on multiple parameters of the fluid medium in which it resides.…”

“…Salophen, salampy and HBAP are prepared and purified following our previous reports, using salicylaldehyde (SD Fine Chemicals, Mumbai, India) and respective aryl amines. 30,32,34,42 Salbn is prepared by dropwise addition of salicylaldehyde (2 equiv.) to a methanolic solution of 1,4-butanediamine (1 equiv., Sigma Aldrich) at room temperature.…”

“…28 Over the last few years, our group has explored a family of Schiff bases (Scheme 1), with the mandate of understanding and optimizing the conditions for obtaining enhanced fluorescence from them, by complexation and aggregation. [29][30][31][32][33][34] It has been established that these compounds exhibit selective enhancement of fluorescence with Zn(II) and Al(III) and that the Al(III) complexes emit more strongly than the Zn(II) complexes in solution. For salophen ((2,2 0 -((1,2-phenylenebis(azaneylylidene))bis(methaneylylidene))diphenol), Scheme 1), this has been explained in the light of opening of additional non-radiative channels in the dimeric Zn(II) complex, in which the ligands are p-stacked.…”