Spiropyrans in Fluid Solutions

In the search for new photochromies, the spirobenzopyran-merocyanine structure suggests many variations. The size of the rings and the nature and 

Authentic N-analogs of spirobenzopyrans, the 1,2-dihydrospiro-2//-quinolines (79) (or their open forms), have never been isolated, despite many attempts during the past 35 years. In reactions with Fischer s base, 5-nitro-2-aminosalicylaldehyde gave no reaction, whereas 2-aminobenzaldehyde gave only a polymer.7 The open form of the desired compound could be considered a quinone monoimine and therefore be expected to have poor stability. 

The quantum yields and kinetics of the photobleaching of these compounds were determined, and their thermal coloration rates and activation energies were measured. The pH dependence of the spectral absorption changes, due to both the shift in the position of the protonation equilibrium between the spiro form and its salt, and the equilibrium between the salts of the spiro form and the open form, were also measured. A detailed analysis of the extensive data led to the spectroscopic identification of the short-lived ground-state cis conformers of the open forms of the five compounds studied. The photobleaching process is a photo trans-cis isomer- 

In attempts to prepare a spiro-2 -oxocine (105), Fischer s base was allowed to react with 2-hydroxycinnamaldehyde and its a-ethyl-5-nitro, 5-bromo, 3,5-dibromo, 3-bromo-5-nitro, and 3,5-dinitro derivatives. As with the oxepines, the dicon-densed product (106) was formed in the first four cases listed (36-72% yield), and the black, crystalline open form (107) of the desired product was formed (69%) with the dinitro derivative. The bromonitro intermediate gave a mixture of the dicon-densed product and the open form of the desired monocondensed product. In this series also, none of the compounds exhibited any photochromic properties.101 

In attempts to prepare 3-acyl-substituted BIPS (113), various salicylaldehydes were condensed with l,3,3-trimethyl-2-formylmethyleneindoline (Fischer s aldehyde). In alcohol, dimethylformamide, tetrahydrofuran, Y-mcthylpyrrolidonc. and hexamethylphosphoramide as the sole solvents, decarbonylation occurred and the only products were the BIPS compounds. However, in dimethyl sulfoxide, 5-nitro-and 3-bromo-5-nitrosalicylaldehydes gave 11 and 5.6% of the desired 3-formyl-BIPS, respectively. The structures were assigned from their IR and NMR spectra. 

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