Spectral Characterization, Photophysics, and Photochemistry of the Four Stereoisomers of 1-(2-anthryl)-4-phenyl-1,3-butadiene

Abstract

Using a synthetic strategy, based on retention of stereochemistry in the reagent cinnamaldehyde, the four geometrical isomers of 1-(2-anthryl)-4-phenyl-1,3-butadiene were obtained and chromatographically purified. Their structures were established by optical and nuclear magnetic spectrometry and confirmed by their photochemical behavior. Their excited state properties were investigated by stationary and pulsed fluorimetric techniques and by laser flash photolysis. This paper reports the spectral characterization of the four isomers and the photophysical and photochemical parameters obtained by irradiation in a nonpolar solvent at different temperatures. The important contribution of adiabatic pathways in the photoisomerization mechanism and the role of an upper excited singlet state in the relaxation properties are discussed. Indication of the presence of at least two conformers was obtained only when exciting at the extreme red onset region of the absorption spectrum.

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

“…1 The photoisomerization in the first excited singlet state (S 1 ) proceeds, at least in part, through an adiabatic mechanism, 3,4 from 1 ZZ* or 1 ZE* to 1 EE*, similar to what has been found for several diarylethenes and diarylbutadienes. [5][6][7][8] The excitation of ZZ leads directly to EE through a 'one photon-two bonds' mechanism that implies the rotation of both the double bonds by absorption of one photon, as previously reported for stilbene-like molecules with more isomerizable double bonds. 3,4,7,8 Moreover, 1 ZZ* and 1 ZE*, that give fast isomerization, hardly deactivate towards the ground state through fluorescence at room temperature, as most compounds with double bonds in cis configuration.…”

Photoisomerization mechanisms and photoselectivity of the stereoisomers of 1-(pyrid-n-yl),4-phenylbuta-1,3-diene

“…The behaviour described for the four stereoisomers in the sensitized experiments, and particularly the formation of photoproducts implying rotation of both double bonds, indicates that adiabatic isomerization pathways are operative also in the triplet manifold. The processes involved can be thus schematized: 3…”

“…3 EE* process. This is indicated by the fact that the quantum yields of the '' one photon-two bonds '' process, implying 3…”

“…1 The emission properties, photoisomerization mechanism and ground state rotamerism 2 have been first investigated for the geometrical isomers of a number of asymmetric diarylbutadienes, particularly the 2-anthryl derivatives. 3 Their photobehaviour has been reasonably interpreted in terms of the competition of the radiative, non-radiative and reactive relaxation processes. The excited state behaviour of the EE and ZE stereoisomers of the three positional isomers of 1-(pyrid-n-yl),4-phenylbuta-1,3-diene (nPPhB, with n ¼ 2, 3 and 4) in the first excited singlet state has been recently reported 4 and compared to that of the parent hydrocarbon, DPhB.…”

Effect of thienyl groups on the photoisomerization and rotamerism of symmetric and asymmetric diaryl-ethenes and diaryl-butadienesElectronic supplementary information (ESI) available: (1) Calculated electronic spectra (transition energy and oscillator strength) and ground state total energy of the rotamers of the trans isomers; (2) Absorption and emission spectra. See http://www.rsc.org/suppdata/pp/b4/b408241a/.

“…50 : 50 partitioning at the perpendicular configuration. 18 The dienes display lower yields, probably because of higher torsional barriers and/or lower frequency factors, as found for other diarylbutadienes 23 and dithienylpolyenes. 3 In this case, the two asymmetric dienes gave two photoproducts, ZE and EZ, with a clear prevalence of the former for the 2T derivative.…”