Síntese de novos agentes fluorescentes: híbridos moleculares doador-aceptor e ligantes carboxílicos

Abstract

This work reports the synthesis of three unprecedented D-A binary molecular hybrids (TF-CONH-Ar), formed by the condensation of fluorescent aromatic amines, an electrondonating subunit (Ar-NH-, D) - where Ar = 9,9-di-hexyl-9H-fluorene, dibenzo[b,d]thiophene, and N-methyl-9H-carbazole - and an electron-accepting subunit, β-carboxy-thiophene (TF-CO-, A), with a promising potential for emission in the near-infrared region. Three conjugated organic ligands based on fluorescent aromatic carboxylic acids (Ar-COOH) were also obtained (where Ar = 9H-fluorene, dibenzo[b,d]thiophene, and dibenzo[b,d]furan). These ligands are promising candidates to act as "antennas" in lanthanide (III) complexes. The three novel molecular hybrids synthesized, N-(9,9-di-hexyl-9H-fluoren-2-yl)thiophene-3-carboxamide (5), N-(dibenzo[b,d]thiophen-3-yl)thiophene-3-carboxamide (6), and N-(Nmethyl-9H-carbazol-3-yl)thiophene-3-carboxamide (7), through the condensation of donor subunits (D), 2-amino-9,9-dihexyl-9H-fluorene (1), 3-aminodibenzo[b,d]thiophene (2), and 3-amino-N-methyl-9H-carbazole (3), with an acceptor subunit (A), thiophene-3-carbonyl chloride (4), exhibited good yields (63 to 81%). Regarding the photophysical behavior of the thiophene carboxamides 5, 6, and 7, two emission bands were observed: the first, with high intensity, was in the violet region (373,9 to 421,0 nm), and the second, with low intensity, was located between the orange and red regions (593,9 to 640,0 nm). Although photoluminescence was not observed in the near-infrared region for the novel D-A molecular hybrids synthesized in this study, they are promising fluorophore candidates in the NIR region upon the formation of ternary D-A-D polymeric hybrids, using EDOT (3,4-ethylenedioxythiophene) as the electron-donating subunit. The three obtained aromatic carboxylic acids, 9H-fluorene-2-carboxylic acid (8), dibenzo[b,d]thiophene-2-carboxylic acid (9), and dibenzo[b,d]furan-2-carboxylic acid (10), showed yields between 28 and 77% and excellent solubility in most employed synthesis solvents, which is uncommon for this class of conjugated ligands. Thus, acids 8, 9, and 10 are important candidates for the synthesis of lanthanide (III) complexes with good solubility in the processing solvents.