Spectral properties of aminoderivatives of benzophenone

Abstract

The absorption spectra at room temperature were measured on Specord UV VIS and SF-26 spectrometers. At the temperature 77~ the absorption and luminescence spectra were recorded by a photographic method with the aid of ISP-28 and ISP-51 spectrographs with a camera with focal length 270 mm. The source of excitation was a DKsSh-1000 xenon lamp; a 365 nm filter and a DMR-4 double monochromator were additionally used to obtain the luminescence spectra. Toluene and n-heptane were used as solvents. The concentration of the substance in solution was varied from 10 -5 to 10 -3 M. The infrared absorption spectra were measured on a UR-20 twobeam automatic spectrophotometer in CCI~ (concentration 5,10 -= M) and in tablets of KBr on a LiF prism. The So ~ S* absorption spectra of derivatives of benzophenone at room temperature are represented by two broad bands. The absorption bands of ortho-aminobenzophenone (o-AB) are somewhat broader than the absorption bands of meta-aminobenzophenone (m-AB). The position of the maximum of the long-wave bands depends weakly on the solvent (Table i), The maximum of the long-wave band of o-AB is shifted by approximately 2380 cm -I into the red region, while the maximum of m-AB virtually coincides with the long-wave absorption band of benzophenone, The integral intensity ofthe long-wave band of m-AB is approximately four times as great as the integral intensity of the band of o-AB. Lowering the temperature to 77~ did not lead to resolution of the vibrational structures of the absorption bands of benzophenone derivatives, The absorption band of benzophenone derivatives in the range of 29,000-26,000 cm -~ coincides with the spectral region of the S*(~ ~,~ § So transition of the benzophenone molecule; -F, l . therefore, by analogy with benzophenone, we asslgned it to an S*: ,, § So transition, kP,~ } In the absorption spectra of benzophenone, we can distinguish a vibrational spectrum in the weak p~* band (progression of the stretching vibration of the C=O group in the exc~ed state approximately 1200 cm-:). As was noted above, the spectra of aminoderivatives of benzophenone are represented by diffuse bands. In our opinion, one of the causes of the blurring of the bands of the ultraviolet absorption spectrum of benzophenone derivatives may be the presence of a hydrogen bond between ~=0 and NH2 groups. There are many experimental studies [11-13] in which it has been shown that the introduction of an amino group into the ortho-position promotes the formation of an intramolecular hydrogen bond; in this case a red shift and broadening of the absorption bands are observed, The introduction of an amino group into the meta- and para-positions hinders or entirely excludes the formation of an intramolecular hydrogen bond. Together with the intramolecular hydrogen bond, the compound o-AB should form an intermolecular hydrogen bond, thanks to the