On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium

Abstract

As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag --> 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.

On the use of β‐carotene as a probe for solvent polarizability

“…and concluded that the influence of solvent polarizability seemingly increases with increasing length of the diphenylpolyene chain. This assumption was later on confirmed by our group using tetra( tert ‐butyl)polyenes (ttbP) to establish a linear relationship between their sensitivity to the polarizability of the medium and the length of the polyene chain. Several reviews of the photophysical behavior of polyenes have discussed this solvatochromic feature; surprisingly, however, they all attributed its discovery mistakenly to Sklar et al .…”

On the empirical scales of organic solvents established using probe/homomorph pairs

“…This is a non-polar hydrocarbon that presents a flat molecular structure, [13] which does not possess any acidity or basicity, and presents a 0-0 component of its first UV/Vis absorption band that is very sharp and very sensitive to the polarizability of the solvent. [14] Later in 2009, using this information, we designed the current scale that allows us to measure indipendently the solvent dipolarity (SdP). [15] To validate the physical meaning and adequacy of our scales, we will analyze the experimentally measured solvatochromism [9][10][11][12] of all probes and their homomorphs, that is, the molecules DMANF, FNF, NI, MNI, TBSB, and DTBSB (Scheme 1).…”

“…This is a non‐polar hydrocarbon that presents a flat molecular structure, [ 13 ] which does not possess any acidity or basicity, and presents a 0‐0 component of its first UV/Vis absorption band that is very sharp and very sensitive to the polarizability of the solvent. [ 14 ] Later in 2009, using this information, we designed the current scale that allows us to measure indipendently the solvent dipolarity ( SdP ). [ 15 ]…”

Absorption to and emission from the excited electronic state 11Bu in long linear all‐trans‐polyenes: The case of ttbP9 and ttbP11

“…As indicated by the studies, we have already carried with these unsaturated hydrocarbons, they are perfectly photostable and therefore allow photophysical investigations. [ 21–23 ]…”