**Objective**  
Classify the provided list of candidates into **NO MORE THAN THREE groups** according to the **[Target_Property_Descriptor]**, or place them all in **ONE group** if the data justify no split.  
Your primary evidence must come from **quantitative, database-level descriptors** (experimental or computed) that are routinely reported for this item type.

**Crucial Instructions**  
1. **Prioritise Quantitative Data**  
   - Use measurable values (e.g., band-gap in eV, toughness in J m⁻³, π→π* gap in nm, redox potential in V, dielectric constant, Young’s modulus, H-bond donor count, etc.).  
   - Cite the numeric range or threshold you rely on (even if you simulate the lookup).

2. **Minimise Intuition**  
   - Do **not** use informal, qualitative knowledge such as “looks polar” or “commonly used as insulator”.  
   - If no direct value exists, derive a proxy that **could** be tabulated (e.g., fraction of heavy atoms, aspect ratio, phonon frequency cutoff) and state the proxy.

3. **Adhere to Requested Categories**  
   - Map each item to the **exact categories** supplied below.  
   - Flag borderline cases and explain which numeric value(s) create the ambiguity.

**Candidate Items to Cluster**  
frag_c : ['1,3-dibromonaphthalene', '2,5-dibromo-3-chlorothiophene', '4,9-dibromo-6,7-dimethyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline', '1-bromo-2-(2-bromophenoxy)benzene', '9,10-dibromo-2-tert-butylanthracene', '1,4-dibromo-2,5-difluorobenzene', '2,5-dibromo-1-benzofuran', '2,5-dibromofuran', "2',7'-dibromo-9,9'-spirobi[fluorene]", '1,5-dibromo-2,4-dichlorobenzene', '2,6-dibromo-1,8-naphthyridine', '1,8-dibromonaphthalene', '9,9-bis(2-ethylhexyl)-2,7-diiodofluorene', '4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole', 'bis(4-bromophenyl)-dimethylsilane', '2,8-dibromophenazine', 'bis(2-bromophenyl)-dimethylsilane', '2,5-dibromopyridine', '9-(2,5-dibromo-4-carbazol-9-ylphenyl)carbazole']
