Is there a single organic molecule that has strong absorbance throughout the visible range? For example a black dye that is based on a single molecule?

  • $\begingroup$ Black dye is normally based on polymeric conjugated systems. $\endgroup$ May 23 '16 at 21:13
  • $\begingroup$ pentacene is a bluish-black powder, suggesting that it does have some adsorbance throughout the visible range... though primarily in red part. $\endgroup$
    – permeakra
    May 23 '16 at 21:26
  • $\begingroup$ Does graphite count as organic? $\endgroup$
    – bon
    May 23 '16 at 21:29
  • $\begingroup$ @bon doesn't graphite's absorption depend on the van der waals gap of the graphene sheets? $\endgroup$
    – Sparkler
    May 23 '16 at 21:43
  • 1

Quite a few dyestuffs will have strong absorption across the visible range of wavelengths, though few will have an entirely even absorbance. This won't matter much is they are concentrated enough and absorb most of the light at each wavelength.

Acid Black 1, for example, shows strong absorbance from the UV to just under 700 nm, which is most of the visible. Absorbance is stronger in the red but overall absorbance is large enough that it is sometimes used in black inks. See this paper for a sample absorbance spectrum:

enter image description here

There are quite a few other dyes with strong absorbance at most visible wavelengths and whether they appear black depends on the concentration.


Short answer: no, not yet

This question has been the focus of intense research for dye-sensitized solar cells and other organic conjugated solar cells. Such a dye would absorb a high fraction of photons and likely improve device efficiency.

Some metal complexes have been found as strong absorbers for the DSSC, starting with the so-called "black dye" ($\ce{[Ru(4,4',4''terpy-(COOH)3)(NCS)3]}$) ~1999.

Suffice to say that I have not seen anything to match the ideal "equal black" profile you mention that's also an organic molecule.

As mentioned in the other answer, there are many organic dyes that are strong absorbers and in high concentration will appear black. This is one reason that "black" pens or markers or inks will become purple or blue or green or mixtures of colors under chromatography.


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