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1. Chromophore

   Linked via "polyenes"

   $\pi \to \pi^*$ Transitions
   These are the most common transitions in organic colorants, found in compounds with extended systems of alternating single and double bonds (polyenes). Increasing the extent of conjugation (the length of the effective $\pi$ system) invariably lowers the $\text{HOMO-LUMO}$ gap, leading to a bathochromic shift (a shift to longer, lower-energy wavelengths). For instance, the shift from carotene (yellow/orange) to [lycopene](/entries/ly…

2. Chromophore

   Linked via "Polyenes"

   | Compound Class | Primary Transition Type | Typical Color Imparted | Associated Structural Feature |
   | :--- | :--- | :--- | :--- |
   | Polyenes (e.g., Carotenoids) | $\pi \to \pi^*$ | Yellow to Red | Extended conjugated chains |
   | Azo Dyes | CT / $\pi \to \pi^*$ | Vibrant Orange/Red | $-\text{N}=\text{N}-$ linkage |
   | Anthraquinones | $\pi \to \pi^*$, CT | Blues and [Viol…