Chemiluminescence of lucigenin in aqueous aliphatic amines

Chemiluminescence of Lucigenin has been studied in aqueous amine solutions. The Chemiluminescence emission spectra are recorded using a Fuess spectrograph. A broad emission band appears in the visible region from 470 to 640 nm having an emission peak of 550 nm at the concentration of 1 × 10-3 M lucigenin. The resolved Chemiluminescence emission band show three peaks having maxima at 510, 555 and 610 nm respectively. The mechanism of Chemiluminescence of Lucigenin is based on Chemiluminescence, fluorescence and absorption of lucigenin in aqueous methyl and ethyl amines.

is observed with lucigenin 8 concentration.The CL intensity of lucigenin [9][10][11] Increased by using solvent such as urea, glycol, glycerol, phenolic compound, pyridine, ammonia and pipyridine.Thus the aprotic solvent not only increases the CL intensity but shift the emission band to a longer wavelength 12 .
It is well know that lucigenin (10, 10dimethyl 9, 9-biacridinium dinitrate (DBA 2+ +2NO 3 2-) shows intense chemiluminescence (CL) emission at 485nm 13 .The CL intensity and peak maxima are depend on the concentration of lucigenin.The CL emission peak of 485 nm shifts to a longer wavelength region as the concentration of lucigenin is increase from 10 -6 to 10 -4 M. Numerous studies [14][15][16][17][18] have been carried out to understand the CL mechanism of lucigenin.Methyl acridon is identified as the end product of lucigenin oxidation when with H 2 O 2 as an oxidant.It has been confirmed 19 by comparing the fluorescence spectrum of N-Methyl acridon with CL emission spectrum of lucigenin at low concentration.Koko  Maeda et al 20 proposed the radical mechanism of CL of lucigenin involving a reduction presses of lucigenin by hydroxide ion.It is interesting to study of CL emission spectra of lucigenin in various aliphatic amines and construct the mechanism by using resolved CL spectra.

EXPERIMENTAL
All the chemicals used in the present investigation are of Anala R grade and lucigenin is procured from Sigma Aldrich laboratories The CL intensity was measured carefully by adding the Hydrogen peroxide to a Pyrex cell containing l0 ml of aqueous lucigenin solution kept in front of a photomultiplier tube (Ip-28) coupled to a faster scalar.The concentration of lucigenin and optimum pH are thus determined by varying the lucigenin concentration and pH of the aqueous amine solutions, respectively.
The CL emission spectra were recorded by continuous addition of hydrogen peroxide to a Pyrex cell containing optimum concentration of lucigenin solution.The Pyrex cell was mounted in front of the slit of a fuess spectrograph.All the optical alignments were made before loading the 400 ASA Kodak film.The exposure time varied from 2 to 4 hours depending on the light output of the CL source.The emission lines from a low pressure mercury lamp were superimposed on the same film after CL exposure was over.The film was developed washed and dried.The spectral distribution was obtained with the help of a Russian Mf microdensitometer.The fluorescence (FL) spectra of lucigenin in aqueous amine solutions were recorded on a spectro-fluorimeter (Model SFM 25) while absorption spectra on a Hitachi spectrophotometer.

RESULTS AND DISCUSSION
The existence of optimum concentration of luminescent material is recognized by Brunighauss 21 .It is therefore necessary to study the concentration dependent of CL of lucigenin.It is observed that the CL intensity increase with increasing concentration of lucigenin in aqueous amines.Moreover CL intensity of lucigenin becomes independent above pH-11.The concentration and pH dependence of CL of lucigenin reported by Maskicwicz and Sogah are shown in Fig. 1 the concentration selected for recording CL emission spectrum of lucigenin is 1×10 -3 M. The physical properties 22 of aliphatic amines, their optimum concentration and their corresponding pH value are summarized in Table 1.In the present investigation the CL emission spectra of lucigenin by using H 2 O 2 as an oxidant without resolution showed an emission peak at 550 nm.Fig. 2 shows the analysis of resolved CL emission spectra of lucigenin in various amines showed three emission bands at 515, 555 and 608nm respectively.Fig. 3 shows complete analysis of CL emission spectra of lucigenin in aqueous amines using H 2 O 2 as oxidant is summarized in Table 2.

Lucigenin (DBA 2+ + 2NO -
3 ) in aqueous solution under go the reduction oxidation reaction in which DBA 2+ is reduced by 2 electron transfer from OH -to produced biracial DBA 2 .via a cation radical DBA +. .The dioxetane 20 is formed by oxidation of biracial DBA 2 .by H 2 O 2 .
The dioxetane decomposed to exited Nmethyl acridone which is the major product of CL reaction emitting light at 515nm.A hipsocromic shift  The three emission bands are explained on the basis of above mechanism.The major product of oxidation of lucigenin is N-methyl acridone which emits at 515nm.A minor product of CL reaction of lucigenin is dioxetane as reported by Buzas 23 .Green light emission at around 555nm is due to the formation of exited dioxetane.From this band it is confirmed that the intermediate species formed in CL of lucigenin is dioxetane.It is well know that lucigenin in alkaline medium is fluorescent.A characteristics fluorescence emission from unreacted lucigenin occurs at a longer wavelength of 615nm due to the transfer of energy from exited N-methyl acridone in CL of lucigenin.