Fluorescent tricyclic β-azavinamidine–BF2 complexes

Boron trifluoride reacted with dipyrid-2-ylamine 6 , its N-methyl and 6,6′-dimethyl derivatives 8 and 10 , and 3,3′,5,5′-tetraphenyl-6-azapyrromethene 13 to give fluorescent β-azavinamidine (1,3,5-triazapenta-1,3-diene) dyes: 10-azapyridomethene–BF₂ complex 5 (λ_f 422 nm, λ_las 426 nm), its quaternary 10-methyl tetrafluoroborate and 4,6-dimethyl derivatives 9 (λ_f 362 nm) and 11 (λ_f 416 nm), and 1,3,5,7-tetraphenyl-8-azapyrromethene–BF₂ complex 17 (λ_f 696 nm). Treating 3,3′,4,4′-tetraphenyl-5,5′,6-trimethylpyrromethene (prepared in situ from ethyl 3,4-diphenyl-5-methylpyrrole-2-carboxylate in a reaction with acetyl chloride) with boron trifluoride gave 1,2,6,7-tetraphenyl-3,5,8-trimethylpyrromethene–BF₂ complex 21 . Absorption for the vinamidine chromophore differed from that for the β-azavinamidine chromophore by a hypsochromic shift of 86 nm in a comparison of pyridomethene–BF₂ complex 3 with its 10-aza derivative 5 and by a bathochromic shift of 105 nm in a comparison of the pyrromethene–BF₂ complex 20 with the 8-azapyrromethene–BF₂ complex 17 .