On the dual fluorescence of α,ω‐diphenylpolyenes from five to seven polyene double bonds

Abstract

From analyses of the UV/Vis absorption, emission and excitation of emission spectra of all-trans-α,ω-diphenylpolyenes with five to seven polyene double bonds (1,10-diphenyldecapentaene, DPP5, 1,12-diphenyldodecapentaene, DPP6, and 1,14-diphenyltetradecaheptaene, DPP7), it is concluded that these compounds do not exhibit a dual S1/S2 fluorescence, as hitherto proposed by ]). The spectral data of DPP5, DPP6, and DPP7 show a unique fluorescence the intensity of which decreases with the increase of the polyene chain length.

On the photo‐activation of the S0 → S1 transition in polyenes

“…Evidence presented from the abovementioned experimental work, and from a series of experiments reported elsewhere, leaves without photophysical support any need to invoke the existence of an electronic excited state 2 1 A g in order to rationalize the polyene photophysics. These pieces of evidence can be summarized as follows: (a) the structural connotations found in the detection of the weak absorption located to the red of the first intense transition 1 1 Ag → 1 1 Bu of the diphenylpolyenes, (b) the noninversion of the first two excited states of the DPH with the increase in the polarizability of the medium, and (c) the absence of two fluorescence bands in all‐trans‐polyenes with six and seven double bonds …”

Photophysics of the electronic states S0 and S1 for the coplanar molecular structures of the α,ω‐diphenylpolyenes DPH and DPO

“…Because it is well established that the structures of α,ω-diphenylpolyenes in their crystalline forms present an all-trans configuration and that these are not perfectly planar molecular structures due in large part to the torsion that their phenyl groups exhibit, this torsion appears to increase with the length of the polyene chain of the compound. [30,41] We believe it is interesting to determine both the absorption and emission spectra of DPH and DPO at temperatures of 293 and 77 K in order to detect possible spectral differences that are assignable to a greater planarity of the molecular structures involved in their spectroscopy.…”

“…However, "we must state that despite all this above-mentioned criticism, at this point in time the accepted photophysical model for polyene compounds is the one proposed by Hudson and Kohler." [22,25,26] In the last 4 years, our laboratory has provided photophysical evidence of α,ω-diphenylpolyenes, [17,[27][28][29][30][31][32][33] which has left unsubstantiated the main arguments by Hudson and Kohler. Our contributions lead inexorably to a photophysical model based on structural changes that starts, under normal conditions, with the excitation of a molecular structure of the nonplanar polyene compound.…”

Carbon disulfide solvent, helping to clarify the Stokes shift in diphenylpolyenes

“…In recent years, our laboratory has provided photophysical evidence of diphenylpolyenes, [ 12–18 ] which has left unsubstantiated the main arguments by Hudson and Kohler based on the existence of an underlying phantom state 2 1 Ag, which hypothetically controls the emission of these compounds. Our contributions lead inexorably to a photophysical model based on structural changes that starts under normal conditions with the excitation of a molecular structure of the non‐plane polyene compound [ 16,18 ] that generates the detected SS.…”