Optical conjugated chains

Gas Phase to Solid State Evolution of the Electronic and Optical Properties of Conjugated Chains A Theoretical Investigation... 

By extension one may say that the power laws (5-7) which determine the magnitude of the linear and nonlinear optical coefficients are consequences of this strong electron-lattice coupling. We now make the conjecture that the time response of these coefficients is severely affected by the dynamics of the electron-lattice coupling in conjugated chains when two or more resonant chemical structures can coexist this is the case for many of the organic chains of Figure 2. 

Commonly, the increase in the conjugation chain length leads to the bathochromic shift of the absorption bands. The optical and photoelectrical properties analysis needs to take into account not only formal polyconjugation following from the molecule chemical structure but effective conjugation defined by sterical factors too. 

Although the 2Ag state is optically-forbidden , efficient B to 2Ag internal conversion causes fluorescence fromthe 2Ag state when the conjugated chain is short enough, en the conjugated chain becomes longer, the energy gap between the B and 2 A states increases, and then, the crossover from the 2A fluorescence to the B fluorescence takes place. Therefore, the detection of the 2A fluorescence becomes extremely difficult when the number of the conjugated double bonds (n) exceeds 9. 

---