bound to CB[8]. In the absence of CB[8] the cyclization reaction does not occur, but only the isomerization of the trans isomer to the cis isomer is observed. Dye tuning The dye-tuning capabilities cucurbiturils possess have been explored by researchers in recent years. In general, it has been found that the confined, low-polarity environment provided by the cucurbiturils leads to enhanced brightness, increased photostability, increased fluorescence lifetimes, and solvatochromism consistent with moving to an environment of lower polarity. Related compounds Inverted cucurbiturils or iCB[x] are CB analogues with one glycoluril repeating unit inverted. In this unit the methine protons actually point into the cavity and this makes the cavity less spacious. Inverted cucurbiturils form as a side-product in CB-forming reactions, with yields between 2 and 0.4%. Isolation of this type of CB compound is possible because it is more difficult to form inclusion compounds that ordinarily form with regular CBs. Inverted cucurbiturils are believed to be the kinetically controlled reaction products because the heating of iCB[6] in acidic medium results in a mixture of CB[5], CB[6] and CB[7] in a 24:13:1 ratio. A cucurbituril cut in half along the equator is called a hemicucurbituril. Systematic name Cucurbit[6]uril's systematic name is Dodecahydro-1H,4H,14H,17H-2,16:3,15-dimethano-5H,6H,7H,8H,9H,10H,11H,12H,13H,18H,19H,20H,21H,22H,23H,24H,25H,26H-2,3,4a,5a,6a,7a,8a,9a,10a,11a,12a,13a,15,16,17a,18a,19a,20a,21a,22a,23a,24a,25a,26a-tetracosaazabispentaleno[1’’’,6’’’:5’’,6’’,7’’]cyclooctyl[1’’,2’’,3’’:3’,4’]pentaleno(1’,6’:5,6,7)-cycloocta(1,2,3-gh:1’,2’,3’-g’h’)cycloocta(1,2,3-cd:5,6,7-c’d’)dipentalene-1,4,6,8,10,12,14,17,19,21,23,25-dodecone. References Supramolecular chemistry Macrocycles Ureas 1905 introductions Substances discovered in the 1900s