Photophysical Properties of Novel Picrate Derivatives – Solvent Effect

Abstract

H and (13)C NMR spectra were recorded for some novel picrate derivatives derived from 3,3-dimethyl-2,6-diarylpiperidin-4-ones and 3-benzyl-2,6-diarylpiperidin-4-one. The photophysical properties of the picrate derivatives were studied in several solvents, which include a wide range of apolar, polar and protic media. The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This is attributed due to the presence of increased electrostatic interaction between N-protonated piperidone ring and picryl anion ring so that the picryl anion ring lies perpendicular to the plane of the N-protonated piperidone ring i.e., non co-planarity. Such a geometrical change in the excited state leads to an important Stokes shift, reducing the reabsorption and reemission effects in the detected emission in highly concentrated solutions. The higher fluorescence quantum yield of the picrate derivatives are observed in polar media.

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“…The organometallic complex show emissionat 503 and 532 nm, and measured PL QY (Φ) was 0.54. Emission due to ligand-centered 3 π-π* state is in vibronic nature whereas from 3 MLCT is in broad shape, [39][40][41][42][43][44] and absence of vibronic structured emission of Ir(PIA) 2 (acac) supports the MLCT emission, and it is further confirmed by its phosphorescence life time 1.60 μs ( Figure 10).…”

“…The intensity of both transitions is almost similar, which shows that 3 MLCT ← S 0 transition is strongly symmetry allowed by spin-orbit coupling. [37][38][39][40][41][42][43][44] The spin-orbit coupling was enhanced by the closeness of π-π* and MLCT states and heavy-atom effect of iridium (III) of Ir(PIA) 2 (acac). The organometallic complex show emissionat 503 and 532 nm, and measured PL QY (Φ) was 0.54.…”

“…The stronger Ir-C bonding interaction of the ligand weakens Ir-C bonds at their trans disposition, and electron rich phenyl rings show strong influence and show trans effect; thus, trans-C,C geometry is thermodynamically higher in energy and kinetically more labile, called transphobia. [41,43]…”