Hi, and thanks for taking a look.
There are well-known Woodward-Fieser rules that allow predicting the absorption peak locations in diene compounds that may have unsaturated substituents attached immediately to them. This allows accounting for only a handful of mutually conjugated bonds. In case of long-chain conjugations (e.g. poly-acetylene, poly-phenylene, and such), the Woodward-Fieser rules don't apply. The bathochromic effect of adding more conjugated bonds to the system seems to become weaker with each added bond; and as the chain grows longer, the absorption peak location seems to asymptotically move towards a finite specific wavelength.
Is there any known way to predict the absorption peak location in such long-chain polyconjugated polymers based on the monomer composition and the chain length? If there is, can it perhaps be extended to the special case of a chain consisting of conjugated alternating chromophores?
Thanks in advance.
Hi Nikolay, the solvent used will be of primary importance of any absorption, so I suggest you try different solvents and go on from there.
The ratio between HOMO-LUMO energy gap and conjugation is inverse. (E~1/N). However, there are many theories which argue that the spatial extent or delocalisation of the excitation is limited by electron vibration coupling (polarons or solitons). In practice, oligomeric/polymeric molecules become deformed with length, and so their effective conjugation length is limited. Polydiacetylenes form excellent single crystals, byu still the excitation energy is limited to ~2eV- possibly by interchain coupling.
- Badges
- Science method
- Similar topics
- Methodology
- Absorption Spectroscopy
- UV-Visible Spectroscopy