QUANTUM-CHEMICAL CI-1 ANALYSIS OF UV ABSORPTION-SPECTRA OF 1H-PYRAZOLO[3,4-B]QUINOLINE SYSTEM

Simulations of UV-absorption spectra in the region of 200 to 360 nm of 1-methyl-3-phenyl-, 1-phenyl-3-methyl- and 1,3-diphenyl-pyrazolo [3,4 -b]quinolines were carried out. The simulations involved CNDO/S-CI-1 c alculations of energies, oscillator strengths and eigenvectors of mono excited singlet states. The UV absorption in the three-fused ring syst em of unsubstited 1H-pyrazolo[3,4b]quinoline (PQ) is very similar to t he UV absorption of two-fused six-membered quinoline or naphtalene sys tems. The very strong absorption in the region of 242 nm belongs to th e B-1(b) band, whereas the most longwavelength maximum at 329 nm is qu alified as the (1)L(b) band. On the contrary, the 1,3-disubstituted PQ derivatives show the UV absorption similar to the acenes with three-f used six-membered system and acridine. The (1)L(a) band is the most lo ngwavelength located maximum. The ova erlapped (1)L(b) band in the UV spectra of three-fused six-membered ring compounds appears in the spec tra of 1-phenyl-3-methyl- and 1,3-diphenyl-derivatives. The position o f the B-1(b) band is the most sensitive to substituent effects from th e 1-position of the system.