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| Content Provider | Royal Society of Chemistry (RSC) |
|---|---|
| Author | Vione, Davide Berto, Silvia Barsotti, Francesco Ghigo, Giovanni |
| Copyright Year | 2017 |
| Abstract | The photophysics and photochemistry of 4-hydroxybenzophenone (4HOBP) are interesting because they can give some insight into the behavior of humic material. Here we show that 4HOBP has a number of fluorescence peaks: (i) an intense one at excitation/emission wavelengths Ex/Em ∼ 200–230/280–370 nm, likely due to an excitation transition from S0 to S5 or S6, followed by S2 → S0 in emission (Sn denotes the singlet states of 4HOBP); (ii) a minor peak at Ex/Em ∼ 270–300/320–360 nm (S0 → S2 in absorption and S2 → S0 in emission), and (iii) very interesting signals in the typical emission region of humic substances, most notably at Ex/Em ∼ 200–220/400–500 nm and Ex/Em ∼ 260–280/400–470 nm (in both cases the emission corresponded to an S1 → S0 transition). The peak (i) (Ex/Em ∼ 200–230/280–370 nm) is quite intense at low 4HOBP concentration values, but it undergoes an effective inner-filter phenomenon. Remarkably, 4HOBP shows fluorescence peaks that arise from S2 → S0 transitions and that do not follow Kasha's rule. Fluorescence is observed in aprotic or poorly protic solvents, and to a lesser extent in aqueous solution. The excited states of 4HOBP, and most notably 4HOBP-S1, are much stronger acids than 4HOBP-S0. Therefore, excited 4HOBP is quickly deprotonated to 4OBP−-S0 in ∼neutral solution, with a considerable loss of the fluorescence properties. Higher fluorescence intensity can be observed under acidic conditions, where excited-state deprotonation is less effective, and in basic solution where the dissociated 4OBP−-S0 form prevails as the ground state. The excited states of 4OBP− are formed directly upon radiation absorption, and being weak bases they do not undergo important acid–base equilibria. Therefore, they can undergo radiational deactivation to produce significant fluorescence emission. |
| Starting Page | 527 |
| Ending Page | 538 |
| Page Count | 12 |
| File Format | HTM / HTML PDF |
| ISSN | 1474905X |
| Volume Number | 16 |
| Issue Number | 4 |
| Journal | Photochemical & Photobiological Sciences |
| DOI | 10.1039/c6pp00272b |
| Language | English |
| Publisher | Royal Society of Chemistry |
| Access Restriction | Open |
| Subject Keyword | Kasha Fluorescence Humic acid Photochemistry |
| Content Type | Text |
| Resource Type | Article |
| Subject | Physical and Theoretical Chemistry |
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