On the first electronic transitions in molecular spectra of conjugated diphenylpolyenes: A reappraisal

On the temperature‐dependent isomerization of all‐trans‐1,6‐diphenyl‐1,3,5‐hexatriene in solution: A reappraisal

“…In several publications, [ 35–38 ] we have shown that the UV/Vis absorption spectra of diphenylpolyenes in solution obtained at different temperatures do not comply with the Mulliken–Rieke rule, [ 39 ] and consequently, these compounds change their molecular structure with temperature. Therefore, the changes in their spectral absorption envelope cannot be assigned only to changes in the polarizability of the medium as Turek et al [ 15 ] do.…”

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

“…As have reported in recent works, [ 13,16–18 ] the Stokes shift presented by diphenylpolyenes will disappear if these compounds adopt an adequate molecular structure. In the molecules that adopt this molecular structure, the origins of the first absorption band and of the emission of the compound practically overlap.…”

“…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. This starting point of the photophysics of these compounds is undoubtedly novel based on the previous reasoning presented by other authors.…”

On the photophysics of a polyene dissolved in n‐alkanes when the temperature drops from 293 to 77 K

“…This information together with other evidence provided in recent years by our laboratory [ 1,2,11–16 ] allows us to draw the following conclusions in order to propose an adequate model to correctly interpret the photophysics of polyene compounds: The position of the first intense peak in the excitation spectrum of the DPO in the six n ‐alkanes used represents a bathochromism that varies linearly with the temperature from 293 to the melting point temperature of the corresponding alkane. This behavior is red‐shifted in parallel fashion as the alkane chain is lengthened, as a result of the alkane's increasing polarizability on lengthening of its chain.The reported increase of the bathochromism with the decrease of the temperature undoubtedly also includes a structural contribution because the phenyl groups in the diphenyl polyenes in liquid solvents present such a small torsion barrier what makes their two phenyl groups are continuously rotating out of the coplanar situation.…”

“…This behavior is red‐shifted in parallel fashion as the alkane chain is lengthened, as a result of the alkane's increasing polarizability on lengthening of its chain.The reported increase of the bathochromism with the decrease of the temperature undoubtedly also includes a structural contribution because the phenyl groups in the diphenyl polyenes in liquid solvents present such a small torsion barrier what makes their two phenyl groups are continuously rotating out of the coplanar situation. [ 11,17 ] Consequently, the aforementioned bathrochromic increase will be the result of two contributions, one generated by the increase in the polarizability of the solvent and the other due to the decrease in the torsion of its phenyl groups that will adopt an average conformation closer to a coplanar with decreasing temperatures. Consequently, the absorption spectrum and also the excitation spectrum in these solutions must be produced contrary to what is commonly accepted [ 18 ] for light absorbing structures of a noncoplanar DPO. b)At temperatures below their melting points, the DPO solutions in these alkanes barely change the position of the discussed peak.…”