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So regarding the chemiluminescence in a glow stick reaction, the glow is due to the unstable compound 1,2-dioxetanedione decomposing into carbon dioxide, releasing energy which is then absorbed by the electrons in the molecules of the dye. This promotes the electron to an ‘excited state’ and when the electrons fall back to their ‘ground state’, they emit photons of light, where the exact energy of the light given off is dependent on the structure of the molecule.

Since I learned in organic chemistry that the more conjugated the molecule, the less energy required to promote the electrons to an excited state, I assume that is the reason why more conjugated systems (in the photo, Rhodamine B) emit lower frequencies of light (red), since lower energy is required to excite the electrons.

Am I correct?

In addition, if that is so, wouldn't the amount of conjugation of dye affect the efficiency of the chemiluminescence reaction? So for example, since more conjugated systems require less energy for the electrons to be excited, they will emit more light with the same amount of energy compared to less conjugated systems that need higher energy (emits higher frequency light).

I have asked my teacher multiple times, but she does not provide me with a satisfying question, I pray for help.

Thank you.

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    $\begingroup$ To my knowledge, the substituents present on the conjugated system also effect colour through "push" and " pull" of electrons, arising from inductive and resonant effects e.g. CN, OMe. This was certainly the case in the early development of oligomeric and polymeric organic LEDs $\endgroup$ – Beerhunter Dec 4 '19 at 0:32
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    $\begingroup$ While first part seems OK, then that's quantum efficiency that you're got into and I doubt it depends on the gap between HOMO and LUMO in any simple way. $\endgroup$ – Mithoron Dec 4 '19 at 1:00
  • $\begingroup$ @Beerhunter Can you give me more detail on this? $\endgroup$ – HirG Dec 4 '19 at 2:00
  • $\begingroup$ First part is straightforward. Second part I don't think the teacher can, see Mithoron comment (that I agree with). $\endgroup$ – Alchimista Dec 4 '19 at 8:34
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The initial chemiluminescent (CL) species transfers its excited state energy to the dye. This depends on the overlap of the CL emission spectrum with the absorption spectrum of the dye and their spatial separation, i.e. better spectral overlap and higher concentration more transfer and more dye emission. (see Forster energy transfer for mechanism). The dyes used have 80-100% fluorescence quantum yield, so v. high chance of emission. The intensity you experience will also depend on how your eyes respond to different colours.

The energy gap in the dyes does not greatly affect their fluorescence efficiency, this is primarily governed by interactions within the dye to produce triplet states which drain energy out of the fluorescent singlet state.

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