Pyrromethene–BF2 complexes as laser dyes: 2

✍ Scribed by Joseph H. Boyer; Anthony M. Haag; Govindarao Sathyamoorthi; Mou-Ling Soong; Kannappan Thangaraj; Theodore G. Pavlopoulos

• Book ID: 102846548
• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 988 KB
• Volume: 4
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/hc.520040107

✦ Synopsis

Pyrromethene-BF, complexes (P-BF,) 7 were obtained from a-uns,ubstituted pyrroles 5 by acylation and condensation to give intermediate pyrromethene hydrohalides 6 followed by treatment with boron trifluoride etherate. Conversion of ethyl cu-pyrrolecarboxylates 4 to a-unsubstituted pyrroles 5 was brought about by thermolysis in phosphoric acid at 160°C, or by saponification followed by decarboxylation in ethanolamine at 18O'C, or as unisolated intermediates in the conversion of esters 4 to pyrromethene hydrobromides 6 by heating in a mixture o f formic and hydrobromic acids. Addition o f hydrogen cyanide followed by dehydrogenation by treatment with bromine converted 3,5,3',5'-tetramethyl-4,4'-diethylpyrromethene hydrobromide 9 to 3,5,-3',5'-tetramethyl-

4,4'-diethyl-6-cyanopyn-omethene hydrobromide 6bb, confirmed by the further conversion to I ,3,5,7-tetramethyl-2,6-diethyl-8-cyanopyrrornethene-BF2 complex 7bb on treatment with boron trifluoride etherate.

An alternation effect in the relative giciency (RE) of laser activity in 3,5,7, dyes depended on the number of methylene units in the n-alkyl substituent, -(CHJ,H, to give RE 3 100 when n = 0,2,4 and RE 65, 85 when n = I ,3. (The RE I00 was arbitrarily assigned to the dye rhodamine 6G). The absence o f fluorescence and laser activity in 1,3,5,7-tetramethyl-2,6- diethyl-8-isopropylpyrromethene-BF2 complex 7p and a markedly diminished fluorescence quantum yield (@ 0.23) and lack of laser activity in 1,3,5,7-tetramethyl-2,6-diethyl-8-cyclohexylpyrromethene-B F ,