Remarkable fluorescence enhancement of benzo[g]chromen-2-ones induced by hydrogen-bonding interactions with protic solvents

Abstract

A coumarin analogue, 8-methoxy-4-methyl-2H-benzo[g]chromen-2-one (MMBC), is almost non-fluorescent in non-polar media, whereas it exhibits dramatically enhanced fluorescence in polar protic solvents. This study investigates the mechanistic features of the significant solvent effects on the fluorescence properties of MMBC and a related compound, 4-methyl-2H-benzo[g]chromen-2-one (MBC), by time-resolved fluorescence and photoacoustic measurements and by theoretical calculations. Time-resolved photoacoustic measurements reveal that the extremely fast non-radiative processes of MBC and MMBC in non-polar solvents can be attributed predominantly to internal conversion. The internal conversion rates of MBC and MMBC are remarkably reduced in a rigid matrix of 3-methylpentane at 77 K, suggesting that internal conversion is a thermally activated process. The photophysical properties of MBC and MMBC examined in selected solvents with different polarities and hydrogen-bond donating abilities show that the internal conversion rate is greatly reduced by hydrogen-bonding interactions with protic solvents. Furthermore, remarkable fluorescence enhancement is observed by adding a small amount of trifluoroethanol to n-hexane solutions of MBC and MMBC, indicating that internal conversion is suppressed by formation of hydrogen-bonded complexes with protic solvents. In light of theoretical considerations based on time-dependent density functional theory (TD-DFT) and INDO/S-CI calculations, the occurrence of fast internal conversion in MBC and MMBC can be explained in terms of the proximity effect, i.e., pseudo Jahn-Teller coupling between energetically close S(1) and S(2) states.

A Series of π‐Extended Thiadiazoles Fused with Electron‐Donating Heteroaromatic Moieties: Synthesis, Properties, and Polymorphic Crystals

“…The calculated k nr values for 6 and 7 ((6.1–15)×10 7 s − ) are significantly smaller than those for 3 ((89–96)×10 7 s − ), whereas the k r values for 6 and 7 are comparable to those for 3 . Time‐resolved photoacoustic measurements gave Φ isc values in toluene of 0.61 and 0.67 for 6 and 7 , respectively, which are almost two‐thirds the value for 3 (see Figures S10–S12 in the Supporting Information) 24. In 6 and 7 , as is the case with 3 , the sum of Φ f and Φ isc is almost equal to 1, within experimental error, which clearly indicates on the basis of the equation Φ f + Φ isc + Φ ic =1, in which Φ ic is the quantum yield of internal conversion, that internal conversion in 6 and 7 barely occurs.…”

Deep Eutectic Solvent Mediated Alkyne‐Carbonyl Metathesis (ACM) Reaction for the Synthesis of 2H‐Chromene Derivatives

“…There are large collection of literature, related to biological properties of 2H ‐chromene derivatives such as antioxidant, anticancer, antitumor, anticancer, anticoagulant, fungicidal and anti‐HIV activity which evidence the wide range of bio‐activity of the motif . In addition, photochromic properties such as fluorescence probe, optical brighter, organic light emission for materials based on 2H ‐chromene have been well studied (figure ) . The structural feature and broad spectrum of biological activities of 2H ‐chromene derivatives has stimulated the synthetic organic chemist and biologist to find an improved synthetic protocol for the preparation of these heterocyclic skeletons in a green synthetic pathway.…”

Microwave-assisted synthesis of 2,8-di(alkyl/aryl)-4,6-dichloro-2H,8H-pyrano[3,2-g] chromene-3,7-dicarbaldehydes and their antimicrobial activity

“…In particular, various chromene derivatives of 2H-chromenes have been reported with important medicinal applications. [15][16][17] Some of them are currently used as drugs, such as bimakalim as an opener of KATP-channels, 18 cannabichromene (CBC) and some 356 VENKATARAMANA et al…”