Fluorescent tricyclic β‐azavinamidine–BF2 complexes

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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 (λf 422 nm, λlas 426 nm), its quaternary 10‐methyl tetrafluoroborate and 4,6‐dimethyl derivatives 9 (λf 362 nm) and 11 (λf 416 nm), and 1,3,5,7‐tetraphenyl‐8‐azapyrromethene–BF2 complex 17 (λf 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.