Aggregation-induced enhancement (AIE) in the photoluminescence quantum yield (PLQY) from 12.5 to 51% in the N,Ndimethylformamide (DMF)-stabilized Au nanocluster (AuNC) system is reported here. The self-assembling of AuNC has been achieved via hydrogen bonding interaction, which is further utilized in designing the AuNC_DCM system for realizing a Forster resonance energy transfer (FRET)-based white LED (WLED), having CIE coordinates of (0.35, 0.29). The solution-processed fabrication strategy used, has given us the liberty to optimize its components for optimal full-spectrum light output. The CIE coordinates of the designed WLED have been improved further to (0.33, 0.32), with a high color rendering index of 93 and correlated color temperature of 5620 K by incorporating a green emitter, namely nitrogen-doped graphene quantum dots (NGQD), in the AuNC_DCM system. The excellent spectral quality of the as-designed WLED and the repeatability of the proposed fabrication method will make the developed AuNCs_DCM FRET conjugate useful in practical photonic applications.

Cavity ring-down spectroscopy (CRDS) was used to measure the absorption cross section of phenyl radicals (C6H5 •) at 504.8 nm (2B1 ← 2A1 transition) in the nitrogen atmosphere at 40 Torr total pressure and 298 K using nitrosobenzene (C6H5NO) as the radical precursor. At 504.8 nm, the absorption cross section was measured to be σphenyl 504.8 nm = (5.7 ± 1.4) × 10–19 cm2 molecule–1. The absorption cross section was independent of the total pressure range (40–200 Torr) over which it was studied with a precursor concentration of (4–5) × 1013 molecules cm–3. In addition to this, the absolute rate coefficients for the reaction of phenyl radicals with methanol were measured over the temperature range of 263–298 K and at 40 Torr pressure with N2 using CRDS. The temperature-dependent rate coefficient for the title reaction over the studied temperature range was obtained to be k263–298 K experiment (T) = (1.38 ± 0.60) × 10–11 exp [−(1764 ± 321)/T] cm3 molecule–1 s–1 with a rate coefficient of k(T) = (3.50 ± 0.32) × 10–14 cm3 molecule–1 s–1 at 298 K. The effect of pressure and laser fluence was found to be negligible within the experimental uncertainties in the studied range. In addition, to complement our experimental findings, the T-dependent rate coefficients for the title reaction were investigated using computational methods. The B3LYP/6-311 + G­(d,p) level of theory was used in combination with canonical variational transition-state theory with small-curvature tunneling to calculate the rate coefficients. The T-dependent rate coefficient in the range of 200–400 K was obtained as k 200–400 K theory (T) = 2.43 × 10–13 exp­[−(478.38/T)] cm3 molecule–1 s–1 with a room-temperature (298 K) rate coefficient of 4.67 × 10–14 cm3 molecule–1 s–1.

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Despite intensive research, the role of the H-bonding environment on ultrafast PET remains illusive. For example, coumarin 153 (C153) undergoes ultrafast photoinduced electron transfer (PET) in electron-donating solvents, in both aniline (AN) and N,N-dimethylaniline (DMA), despite their very different H-bonding abilities. Thus, donor-acceptor (AN-C153) H-bonding may have only a minor role in PET (Yoshihara and co-workers, J. Phys. Chem. A, 1998, 102, 3089). However, donor-acceptor H-bonding may be somehow less effective in the neat H-bonding environment but could become dominant in the presence of an inert solvent (Phys. Chem. Chem. Phys., 2014, 16, 6159). We successfully applied and tested the proposal here. The nature of PET modulation of C153 in the presence of a passive component cyclohexane is found to be very different for aniline and DMA. Upon addition of cyclohexane to DMA, the PET process gradually becomes retarded but in the case of AN, the PET rate was indeed found to be accelerated at some intermediate composition (mole fraction of aniline, XAN∼ 0.74) compared to that of neat aniline. It is intuitive that cyclohexane may replace some of the donors (AN or DMA) from the vicinity of the acceptor and, thus, should disfavour PET. However, in the hydrogen bonding environment using molecular dynamics simulation, for the first time, we show that the average number of aniline molecules orienting their N-H group in the proximity of the C=O group of C153 is actually higher at the intermediate mole fraction (0.74) of aniline in a mixture rather than in neat aniline. This small but finite excess of C153-AN H-bonding already present in the ground state may possibly account for the anomalous effect. The TD-DFT calculations presented here showed that the intermolecular H-bonding between C153 and AN strengthens from 21.1 kJ mol(-1) in the ground state to 33.0 kJ mol(-1) in the excited state and, consequently, H-bonding may assist PET according to the Zhao and Han model. Thus, we not only justified both the theoretical prediction (efficient H-bond assisted PET within the C153-AN pair) and experimental observation (minor H-bond assisted PET in neat solvent) but also established our previous hypothesis that an inert co-solvent can enhance the effect of H-bonding from molecular insights.

The thermal reaction between nitrogen dioxide and phenol in the gas phase under anaerobic conditions has been investigated by diluting the reactants in dry nitrogen in a glass reaction vessel. Infrared spectroscopic analysis reveals that nitric acid, nitric oxide, and o-nitrophenol are the major products of the reaction. The kinetic analysis reveals the reaction stoichiometry as 3NO2 + PhOH → HNO3 + NO + o-nitrophenol, and the corresponding reaction enthalpy is Δr H 0 = −44.82 kcal/mol. Reaction monitoring by NO2 concentration variation shows that HNO3 formation is linearly correlated with the effective concentration of the nitrogen dioxide dimer (N2O4) formed, and the overall reaction follows a second-order kinetic behavior with respect to N2O4 and phenol, and the estimated rate constant value is (3.53 ± 0.56) × 10–18 cm3 molecule–1 s–1 at 298 K. In the presence of excess NO2, the reaction shows a pseudo-first-order kinetic behavior with a rate constant of (6.67 ± 0.12) × 10–3 s–1. The electronic structure calculation predicts that the N2O4–phenol complex can have multiple conformational minima, and in the lowest-energy conformer, the orientation of the two NO2 molecules about the phenolic −OH group is similar to that of the charge-separated asymmetric ONONO2 dimer of NO2. A radical mechanism has been ruled out, as HONO has not been identified as a product. To the best of our knowledge, the formation of o-nitrophenol in the gas-phase reaction between phenol and NO2 is reported here for the first time. The atmospheric implication of the reaction has been discussed.