Conformer-specific and two-fold adiabatic photoisomerization of ZZ-1,4-di-(2-quinolylethenyl)benzene

Abstract

Irradiation of the ZZ stereoisomer of 1,4-di-(2'-quinolylethenyl)-benzene was found to cause direct adiabatic (one photon-two bond) isomerization to a product having the same lifetime as the EE isomer but a rather different spectrum with respect to that obtained by direct excitation of the EE one. To clarify this unexpected behaviour, the conformational equilibria of the EE stereoisomer have been studied in non-polar solvent by fluorimetry. The most abundant conformers, formed by the hindered rotation of the condensed-ring groups around the quasi-single bond with the ethenic carbons, have been characterized by the selective effect of the excitation energy on the fluorescence spectrum. The combined application of the principal component analysis allowed the separation of the spectral properties of three conformers to be achieved. Information on their structures was obtained by theoretical calculations. The results of the present conformational study clearly indicated that the fluorescence spectrum of the photoproduct of ZZ belongs to a specific component of the conformer mixture of the EE isomer.

Adiabatic Pathways in the Conformational and Geometrical Photoisomerizations of the 1,2-Distyrylbenzene Isomers

“…The shortest lifetime (τ F,3 ), dependent on temperature, was attributed to the ZE(B) conformer, because it is the unique rotamer that can adiabatically isomerize to EE (see below). The adiabatic cis → trans photoisomerization takes place through the classic “one bond flip” mechanism, which produces the geometrical isomer keeping the same conformational geometry: 1 ZE(B)* → 1 EE(B)*, as found for diarylethenes − and heteroanalogues of distyrylbenzene. , …”

“…The adiabatic cis f trans photoisomerization takes place through the classic "one bond flip" mechanism, which produces the geometrical isomer keeping the same conformational geometry: 1 ZE(B)* f 1 EE(B)*, as found for diarylethenes [40][41][42][43][44][45][46][47] and heteroanalogues of distyrylbenzene. 46,48 The torsional barrier of this rotamer-specific process was derived by the Arrhenius-type equation: in the limited temperature range 173-130 K, as shown in Figure 10. The plot in the inset shows a linear trend and led us to derive the following Arrhenius parameters: 1.1 × 10 12 s -1 and 12.1 kJ mol -1 for the frequency factor and energy barrier, respectively.…”

Molecular structure, FT-IR, FT-Raman, NBO, HOMO and LUMO, MEP, NLO and molecular docking study of 2-[(E)-2-(2-bromophenyl)ethenyl]quinoline-6-carboxylic acid

“…They possess antiproliferative [6], anti-neoplastic [7], and cytotoxic properties [8]. Quinolines have been detected in meteorite extracts, and in general quinolines are of astrobiological interest, since this class of molecule includes nucleo bases, basic components of nucleic acids [9,10]. Quinoline derivatives could be used as dopants in the polymer-LED materials [11].…”

(2Z)-2-(4-Methylphenyl)-3-(2-naphthyl)prop-2-enenitrile

“…For background on the commercial importance and applications of styryl dyes, see: Haidekker et al (2001); Hamer (1964); Li et al (1998); Makoto et al (2000a,b); Mousnier et al (2004); Park et al (2001); Pommeret et al (1995); Spalletti (2004). For reference structural data, see: Allen et al (1987).…”

“…Styryl dyes are of commercial importance, not only because of their applications as pigment, but also due to their high technology applications, such as sensitizers formerly (Hamer, 1964), electroluminescence (Makoto et al, 2000a,b), photochromism (Spalletti, 2004), photography (Li et al, 1998), fluorescent probes (Haidekker et al, 2001), optical recording materials (Park et al, 2001), laser dyes (Pommeret et al, 1995) and in the field of medication (Mousnier et al, 2004).…”