Two Photon Absorption Cross‐Section Of New Fluophore Compounds

Abstract

This study is a continuation of previous work carried by our group to synthesize and develop new fluophore compounds that could be used in fluorescence light microscopy for imaging biological molecules. Marking biological cells by such fluophores allow real time observation of single molecules.We synthesized and determined the absorption and emission spectra of the following new fluophores:( L1 ) 4‐Amino‐2‐oxo‐2H‐pyrido[1,2‐a]pyrimidine‐3‐carbothioic phenyl‐amide.( L9 ) 3‐(2‐benzenesulfonyl‐3‐dimethylamino acryloyl) coumarine.( L11 ) 1‐(4‐bromophenyle)‐4‐(coumarin‐3‐carbonyl)‐1H‐pyrazole‐ 3 ‐ carboxylic acid ethyl ester.The absorption spectra are found to peak at wavelengths 285, 358 and 370 nm. [for (L1)], 285, 320 and 360 nm. [for (L9)] and 285 and 360 nm. [for (L11)] Emission lines are observed at 486 nm., 430 nm. and 470 nm for ( L1 ), (L9) and (L11), respectively. These emission lines peaked when (L1), (L9) and (L11) were excited by 370,366 and 360 nm, respectively. This means that all three fluophores could be excited by two photon absorption (TPA) from IR laser of wavelength 730+− 10 nm. or three photon absorption (THPA) of IR laser at 1064+−20 nm. nearly without tuning. Multiphoton excitation of fluophors marking biological samples is advantageous over single photon excitation. The (TPA) and (THPA) fluorescent intensities have been measured for the three fluophors in DMF solution at different concentrations using both 90 femtosecond Ti‐sapphire laser at powers up to 250 MW and 7 nanosecond Nd:YAG laser up to 10 MW. The estimated (TPA) cross‐sections are of the order of 10–39 cm2 / photon and the (THPA) cross‐sections are less by a factor more than 10 times that of (TPA).