Two molecules, 1-hydroxypyrene-2-carbaldehyde (HP) and 1-methoxypyrene-2-carbaldehyde (MP) were explored. We investigated their photophysical properties, using experimental transient absorption and theoretical density functional theory/time-dependent density functional theory (DFT/TDDFT). HP and MP have similar geometric conformations but exhibit entirely different photophysical properties upon excitation into the S1 state. In contrast to traditional excited state intramolecular proton transfer (ESIPT) in molecules that exhibit either single or dual fluorescence, HP has an unusual non-fluorescent property. Specifically, the ultrafast ESIPT process occurs in 158 fs and is followed by an intersystem crossing (ISC) component of 11.38 ps. In contrast to HP, MP undergoes only an 8 ps timescale process, which was attributed to interactions between solute and solvent. We concluded that this difference arises from intramolecular hydrogen bonds (IMHBs), which induce drastic structural alterntion upon excitation.

No abstract

In the present paper, a "light-up" chemsensor with a high specificity for carbon dioxide detection using a pyrimido[1,2-a]benzimidazole derivative (P1H) in liquid media has been developed. The results show that P1H reacts with carbon dioxide activated by a basic ion to form a carboxylic acid compound (P1-COOH). These results also provide a possible method for carboxylation reactions of P1H using carbon dioxide based on a vinyl carbanion. The complete reaction mechanism cycle was also described using DFT calculations.