Nonfluorescent 4,4',5,5'-tetramethyl- and 4,5,4',5'-bistetramethylene
biimidazol-2-yls 5 and 6 combined with boron trifluoride to give the t
etramethyl and bis-tetramethylenebiimidazol-2-yl-BF2 complexes 9 and 1
0 isolated as strongly fluorescent BF3 salts, lambda(f) (dichlorometha
ne): 377 nm PHI 0.93 and 386 nm PHI 0.90. Similarly, fluorescent biben
zimidazol-2-yl 7, lambda(f) (ethanol), 370 nm PHI 0.14, gave a BF2 com
plex 11 isolated as a BF3 salt lambda(f) (ethanol), 417 nm PHI 0.68.