Excited-State Dynamics and Two-Photon Absorption Cross Sections of Fluorescent Diphenyl-Tin^IV Derivatives with Schiff Bases: A Comparative Study of the Effect of Chelation from the Ultrafast to the Steady-State Time Scale

Abstract

Schiff bases bearing an intramolecular hydrogen bond are known to undergo excited-state intramolecular proton transfer and E-Z isomerization, which are related to their thermochromism and solvatochromism properties. In this study, we explored these ultrafast photoinduced processes for two doubly hydroxylated Schiff bases, salicylidene-2-aminophenol and 2-hydroxynaphthylmethylidene-2-aminophenol. From comparisons with our previously reported results for the parent monohidroxylated Schiff base salicylideneaniline, we were able to establish the lack of an effect of a second intramolecular hydrogen bond in the excited-state intramolecular proton-transfer process. Moreover, we synthesized and studied the photophysics of 14 diphenyl-tin(IV) derivatives with Schiff bases with the same framework as the former two. In these organometallic compounds, we observed an increase of more than 50 times in the excited-state decay times in comparison with those of the free ligands. This finding is attributed to the coordination with the metallic center, which restricts the fluctuations of the geometry of the organic Schiff base skeleton. The emission bands of these complexes can be easily tuned through substitutions at the Schiff base ligand and can be made to be centered well above 600 nm. The much enhanced emissive behavior of all diphenyl-tin(IV) derivatives allowed the study of several properties of their electronically excited states, including the effects of different substituents on their femtosecond and picosecond dynamics. Considering potential applications, we also performed transient absorption experiments to assess the wavelength interval for stimulated emission of this type of compound. Finally, we determined their two-photon absorption cross sections in the 760-820-nm range by measuring their two-photon induced fluorescence excitation spectra. Mainly, our results illustrate that the diphenyl-tin(IV) moiety, thanks to its size and its coordination mode with a single Schiff base, can be coordinated to this versatile framework to obtain tunable optical properties wherein the emissive states can have lifetimes on the nanosecond time scale.

State of the Art of Boron and Tin Complexes in Second- and Third-Order Nonlinear Optics §

“…Although the maximum was found at around 750 nm in the three solvents, in chloroform the TPA response is enhanced ( Figure 58) and it is possible to observe a second absorption at 1000 nm that is roughly observed in DMSO and THF. This is explained because the two-photon excitation fluorescence comes from the lowest excited state S1 [48] as reported by Peon for this type of complex [109]. In this case, the excited state is accessible through excitation at the bands located around 400 nm and 500 nm in the OPA spectra explaining the presence of the second band.…”

“…Diorganotin Schiff bases are another type of tin derivatives capable of third order NLO properties. Peon et al [109] described a series of diphenyl tin(IV) Schiff bases (Figure 54), the fluorescence in these complexes are up to 50 times larger than the free base due to the rigidity imposed by the tin center. Li et al [108] reported the study of tetrachloro (1,10-phenanthroline-N,N') tin(IV) listed in Table 9 and their NLO properties.…”

“…Diorganotin Schiff bases are another type of tin derivatives capable of third order NLO properties. Peon et al [109] described a series of diphenyl tin(IV) Schiff bases (Figure 54), the fluorescence in these complexes are up to 50 times larger than the free base due to the rigidity imposed by the tin center. As expected, the naphthalene derivatives are red shifted in the UV-Vis spectra; also in both derivatives, large red shifts are observed when electron-donating groups are located at the meta position to the imino group, and with electron-withdrawing groups in the para position to the imino.…”

Free radical reactions with the extract of brassica family

“…The results corroborate the somewhat similar findings by Peón et al for photochemical properties of coumarins, Schiff bases, etc. (Esquivelzeta-Rabell, Peon, & Cuevas, 2009;Morales-Cueto, Esquivelzeta-Rabell, Saucedo-Zugazagoitia, & Peon, 2007;Rodriguez-Córdoba, Zugazagoitia, Collado-Fregoso, & Peon, 2007;Zugazagoitia et al, 2010).…”

A new fluorescent sensor for Zn2+ based on diarylethene with a 4-diethylamino-salicylaldehyde Schiff base unit

“…On the other hand, Schiff bases with an intramolecular hydrogen bond have been extensively used as model systems to study fundamental photophysical processes, such as excited‐state intramolecular proton transfer (ESIPT), photochromism, solvatochromism, and thermochromism . This kind of derivatives could also act as versatile chelating ligands to complex with metal ions . Recently, some fluorescent sensors based on diarylethenes with a Schiff base unit have been reported .…”