The Synthesis And Properties Of The Benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxyl Ic Acid Derivatives

Six benzimidazo[2,1-a]be-nz[de]isoquinoline-7-one-12-carboxylic acid derivatives were synthesized in this paper. It is 1-benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxyl-4-pyridin-2-ylpiperazine(Z1), 1-benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12- carboxyl-4-pyridin-4-ylpiperazine(Z2), 1-benzimidazo[2,1-a]--benz[de]isoquinoline-7-one-12-carboxyl-4-pyrimidin-2-ylpiperazine(Z3), 1-methylpiperidin-4-ylbenzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylate(Z4), N’-pyridin-2-ylbenzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-hydrazide(Z5) and N-[2-(dimethylamino)ethyl]benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylate(Z6), respectively. Then H1 and H2 were obtained with the quaternization of Z5 and Z6 respectively. We analyzed the optical properties of these compounds and found seven of them can act as sensors for pH or metal ions.Benzimidazo[2,1-a]be-nz[de]isoquinoline-7-one-12-carboxylic acid derivatives Z1 and Z2 containing piperazidine have response for pH and they have similar curves of fluorescent intensity for p H. The sigmoid responses cover the acidic from 5.80 to 1.80 of Z1 and from 9.10 to 4.50 of Z2 respectively. The protonation of Z1 and Z2 induced more than 110-fold and 20-fold increase of fluorescence intensity and the corresponding p Ka are 3.52 and 6.88, respectively. In addition, the sensor Z1 was also employed as a turn-on fluorescent probe for the detection of Fe3+ in Tris–HCl buffer solution and Kd was obtained as 9.3×10-5. Additionally, the detection limit of Z1 for Fe3+ reached 2.5 × 10-6 M. The reason of the difference between Z1 and Z2 is that the nitrogen in piperazidine of Z1 is easier for complex with metal ions than Z2.Benzimidazo[2,1-a]be-nz[de]isoquinoline-7-one-12-carboxylic acid derivatives Z4 containing hydrazine have response for Cu2+ with high sensitivity and high selectively. An obvious fluorescent enhancement can be observed with the addition of Cu2+ in the solution of Z4. The complex ratio between Z4 and Cu2+ was stydied as 1:1.Benzimidazo[2,1-a]be-nz[de]isoquinoline-7-one-12-carboxylic acid derivatives Z5 and Z6 containing ester group can act as “on-off” prober through the protonation and deprotonation. H1 and H2 can be dissolved in water which had potential for the detection in biological and live cells. The carboxylate oxygen in H1 and H2 were easy to hydrolyze under strong alkali condition which induced the changes of the fluorescent spectra and absorption spectra. This kind probers as dynamic test sensors is positive for the detection of water pollution. It’s worth mentioning that the process of the hydrolysis is reversible.The detection process of Z1, Z2, Z5 and Z6 for pH can be explained by PET mechanism. The mechanism of fluorescence sensing as well as the geometrical structure and electronic structure of the sensors were rationalized using DFT/TDDFT calculations.