p-Methoxy Azobenzene Terpolymer as a Promising Energy-Storage Liquid Crystal System

ACKNOWLEDGMENTS OKAZ, JH, and ARI would like to acknowledge the Sultan Qaboos University for its support through His Majesty’s Trust Fund for Strategic Research (SR/SCI/CHEM/18/01) and Internal Grant (IG/SCI/CHEM/21/03). SMA and NFKA would like to acknowledge Malaysian Ministry of Higher Education for the grant number 600-IRMI/FRGS 5/3 (374/2019). AMF would like to acknowledge the Carnegie Trust for the Universities of Scotland, for the Research Incentive Grant RIG008586, the Royal Society and Specac Ltd., for the Research Grant GS\R1\201397, the Royal Society of Chemistry for the award of a mobility grant (M19-0000), and the Royal Society of Edinburgh and the Scottish Government, for the award of a SAPHIRE project.Peer reviewedPostprin

Application of graphene oxide based Microfiber-Knot resonator for relative humidity sensing

A relative humidity (RH) sensor is proposed and demonstrated using a micro-knot resonator (MKR) enhanced with a layer graphene oxide (GO) coating. The MKR is fabricated by means of tapering a standard fiber, with the GO coating added by the drop-cast method. The proposed sensor is tested for an RH range of between 0% and 80% at 20% intervals, and the configurations with and without the GO coating achieve sensitivities of 0.0104 nm/% and 0.0095 nm/%, respectively. The MKR configuration without the GO coating has a linear response correlation coefficient of 0.9098 and a resolution of 0.1%, while the configuration with the GO coating has a linear response correlation coefficient of 0.9548 and a resolution of 0.096% which is better. The proposed sensor has multiple applications, especially in the area of climate and atmospheric measurement and monitoring

Studies on the basic building blocks of light-harvesting complexes using ultrafast two-dimensional electronic spectroscopy

This dissertation describes the development of ultrafast two-dimensional electronic spectroscopy (2DES) using pump-probe geometry and its application in interrogating the underlying femtosecond to picosecond dynamics of basic building blocks in plant light- harvesting complexes (LHC). In the second chapter of this thesis, we provide the description and development of 2DES using a partially collinear geometry. The procedure for post analysis such as conversion of raw data into a purely absorptive 2D data was included in this part of the thesis. The application of 2DES is divided here into three main chapter. In chapter 3, we aims to investigate the effect of finite bandwidth of the interaction pulses in retrieval of the FFCF from 2D spectrum using three different methods (CLSω1, CLSω3, ellipticity). Although all of the methods show correct values in broad excitation bandwidth, our results show that it does not hold true when the excitation bandwidth becomes narrower than the studied absorption band. We used Chl a molecules to test and show that with the help of simulation of the 2D spectra, it is possible to recover the FFCF using any of these methods. Chl a and Chl b are major constituent pigments in LHC complexes. The primary roles of Chl molecules is to absorb light and transfer the energy on a sub-picosecond timescale to the reaction center for the light-chemical energy conversion. It is well established that proteins surrounding Chl molecules play a significant role in optimizing this process. Therefore, understanding the effect of local environment on Chls electronic transition is an important subject to study. 2DES provides a remarkably sensitive tool to study the solute-solvent interaction with high spectral and time resolution. Accompanied by the center line slope (CLS) analysis, in chapter 4, we elucidate the spectral diffusion dynamics of Chlorophyll a (Chl a) and Chlorophyll b (Chl b) in various chemical environments. 2DES was used to measure the frequency fluctuation correlation function (FFCF) of Chl a and Chl b electronic transition. Three time scales and amplitudes of the frequency fluctuations were recovered for the lowest excited state of Chl ranging from hundreds of femtoseconds to picosecond timescales and assigned as the solvation dynamics and spectral diffusion. By measuring them in various solvents, our results revealed significant differences in the extent of inhomogeneous broadening depending on the solvent used, with the biggest contribution of inhomogeneous broadening being due to the polar hydrogen bond solvent and smallest due to the nonpolar solvents. Interestingly, by comparing the results between Chl a and Chl b, our measurements indicated an effect of substituent group in porphyrin ring at position 7 on the rate of relaxation dynamics from an initially inhomogeneous broadening becoming more homogeneous at later Tw (population time). Such evolution was found to be faster for Chl a than Chl b as described in the chapter 4 of this thesis. In the last part of this study (Chapter 5), we utilized 2DES to observe the mechanism of population transfer from the Qx band (S2 state) to the Qy band (S1 state) in Chl a molecule. An ultrafast relaxation from Qx to Qy band was observed to take place in less than Tw=150 fs. Furthermore, observing the cross peak after excitation of the Qx band reveals the type of correlation between the two transition dipole moments. Our results indicate that the Qx and Qy band exhibit minimal correlation even at very short population times. We suggest a possible mechanism explaining lack of the correlation that is based on the fact that the Qx and Qy transition dipole moments are orthogonally oriented with respect to each other.Doctor of Philosoph

Measuring the ultrafast correlation dynamics between the Q x and Q y bands in chlorophyll molecules

We use two-dimensional electronic spectroscopy to measure the ultrafast correlation dynamics between the Q x and Q y transitions in chlorophyll molecules. We derive a variation to the center line slope method to quantify the frequency fluctuation cross-correlation function, C xy( Tw). Compared with the frequency fluctuation correlation function of the Q y transition, we observe that there is only a minimal correlation between the Q x and Q y transition, even at the ultrashort timescale of ∼100 fs, which then decays to zero in a time scale of ∼2 ps.Ministry of Education (MOE)Accepted versionThis work is supported by grants from the Singapore Ministryof Education Academic Research Fund (Tier 2 MOE2015-T2-1-039 and Tier 1 RG16/15). M.F.K. acknowledges funding from the Ministry of Education Malaysia and the SLAB/SLAI fellowship scheme from the University of Malaya. Fruitful discussions with Maxim Gelin and Yuan-Chung Cheng are acknowledge

The effect of laser pulse bandwidth on the measurement of the frequency fluctuation correlation functions in 2D electronic spectroscopy

Several methods have been proposed to obtain the frequency fluctuation correlation function (FFCF) of a transition from the 2DES spectra without complicated fitting procedures. Although all were shown to give correct values in idealized conditions, this might not be applicable in real experimental circumstances. Here, we observe the effects of using different bandwidth excitation pulses in three commonly used methods: ellipticity, center line slope of slices along excitation (CLSω1) and detection (CLSω3) frequencies. The studies were performed on the Qy transition of chlorophyll a. We show that the CLSω3 method gives consistent results for all bandwidths used. For the other two methods, the recovered FFCF values decrease in magnitude with decreasing excitation pulse bandwidths. We also show that by applying the simplified expressions derived by Do et al., incorporating finite pulses in 2DES spectra simulation, we can recover accurate FFCFs using any of these methods

Revealing the excitation energy transfer network of Light-Harvesting Complex II by a phenomenological analysis of two-dimensional electronic spectra at 77 K

Energy equilibration in light-harvesting antenna systems normally occurs before energy is transferred to a reaction center. The equilibration mechanism is a characteristic of the excitation energy transfer (EET) network of the antenna. Characterizing this network is crucial in understanding the first step of photosynthesis. We present our phenomenology-based analysis procedure and results in obtaining the excitonic energy levels, spectral linewidths, and transfer-rate matrix of Light-Harvesting Complex II directly from its 2D electronic spectra recorded at 77 K with waiting times between 100 fs to 100 ps. Due to the restriction of the models and complexity of the system, a unique EET network cannot be constructed. Nevertheless, a recurring pattern of energy transfer with very similar overall time scales between spectral components (excitons) is consistently obtained. The models identify a "bottleneck" state in the 664-668 nm region although with a relatively shorter lifetime (similar to 4-6 ps) of this state compared to previous studies. The model also determines three terminal exciton states at 675, 677-678, and 680-681 nm that are weakly coupled to each other. The excitation energy equilibration between the three termini is found to be independent of the initial excitation conditions, which is a crucial design for the light-harvesting complexes to ensure the energy flow under different light conditions and avoid excitation trapping. We proposed two EET schemes with tentative pigment assignments based on the interpretation of the modeling results together with previous structure-based calculations and spectroscopic observables. Published under license by AIP Publishing

Temperature Dependence of the Energy Transfer in LHCII Studied by Two-Dimensional Electronic Spectroscopy

We measured two-dimensional electronic spectra of light-harvesting complex II (LHCII) at various temperatures (77, 110, 150, 230, and 295 K) under conditions free from singlet-singlet annihilation. We elucidated the temperature-dependent excitation energy transfer dynamics in the Chl a manifold of LHCII. Global analysis revealed that the dynamics can be summarized in distinct time scales from 200 fs up to 15 ps. While the fastest dynamics with a decay time of similar to 0.2-0.3 ps are relatively temperature-independent, the lifetimes and relative contributions of slower components showed considerable temperature dependence. The slowest time scale of equilibration with the lowest-energy Chl a increased from similar to 5 ps at 295 K to similar to 15 ps at 77 K. The final excited state is independent of initial excitation at 230 K and above, whereas static energy disorder is apparent at lower temperatures. A clear temperature dependence of uphill energy transfer processes was also discerned, which is consistent with the detailed-balance condition

Steady-state spectroscopy and ultrafast dynamics of flavylium derivatives in the red and near-infrared spectral region

In an effort to enhance the absorption and fluorescence of flavylium in the red and near-infrared (NIR) spectral region, we synthesized a 2′-hydroxyflavylium derivative (FLV-OH) with a rigid electron donating julolidine group attached to position 7 and examined its ground and excited states spectroscopy by absorption, fluorescence, ultrafast dynamics, and by density functional theory (DFT). The current results indicate that FLV-OH has spectroscopic properties that make it suitable for many applications such as a potential light harvesting dye in solar cell.Published versio

Evidence of Increased Hydrophobicity and Dynamics inside the Tail Region of Glycolipid Self-Assemblies Using 2-n-Alkyl-Pyrene Derivatives to Probe Different Locations

New designer biofluorophores are being increasingly used in the investigation of complex cellular processes. In this study, we utilized new derivatives of pyrene (Py), i.e., 2-n-alkyl-pyrenes (Py-C4 and Py-C8), in order to probe different regions inside the hydrophobic tail of n-dodecyl β-d-maltoside (βMal-C12) in two different phases (cubic ↔ lamellar). Although the sensitivity to the local environment is reduced compared to that of Py, attaching C4 and C8 at the 2-position of Py can provide a possible means to probe the local hydrophobicity in different parts of the tail region. The absence of excimer fluorescence and the ratio of the vibronic fluorescence peak intensities (I1/I3) in a lipid environment indicate the existence of Py as monomers in the hydrophobic region, similar to hydrophobic solvation, yet close to the headgroup region. When Py is replaced by Py-C4 and Py-C8, there is a small increase in hydrophobicity (reduction in I1/I3) as the Py moiety is pulled deeper inside the tail region of both cubic and lamellar phases. The larger space of the tail region in the lamellar phase is reflected as more local hydrophobicity measured by the probes which can penetrate deep inside, whereas the curved structure of the cubic phase limits the available space for the probes. Three fluorescence lifetime components were measured in lipid, indicating the heterogeneous nature of the hydrophobic region. In the lamellar phase, a large reduction in the average lifetime value, led by the long decay component, was measured for Py-C4 (reduction by 25%) and Py-C8 (45%) compared to that of the parent Py. This observation suggests the presence of a mechanism of interaction more collisional than static between the Py moiety and the tail region of the bilayer unit due to the ample space provided by the lamellar phase as the probe is buried deeper inside the hydrophobic region. A much smaller effect was observed in the cubic phase and was correlated with the tight environment around the probes, which stems from the increased curvature of the cubic phase. The current results provide a deeper understanding of the hydrophobic region during phase transition of lipid self-assembly which is important for better control during the process of membrane-protein crystallization

Energy-Efficient Wireless Sensor Network with an Unequal Clustering Protocol Based on a Balanced Energy Method (EEUCB)

A hot spot problem is a problem where cluster nodes near to the base station (BS) tend to drain their energy much faster than other nodes due to the need to perform more communication. Unequal clustering methods such as unequal clustering routing (UDCH) and energy-efficient fuzzy logic for unequal clustering (EEFUC) have been proposed to address this problem. However, these methods only concentrate on utilizing residual energy and the distance of sensor nodes to the base station, while limited attention is given to enhancing the data transmission process. Therefore, this paper proposes an energy-efficient unequal clustering scheme based on a balanced energy method (EEUCB) that utilizes minimum and maximum distance to reduce energy wastage. Apart from that, the proposed EEUCB also utilizes the maximum capacity of node energy and double cluster head technique with a sleep-awake mechanism. Furthermore, EEUCB has devised a clustering rotation strategy based on two sub-phases, namely intra- and inter-clustering techniques, that considers the average energy threshold, average distance threshold, and BS layering node. The performance of the proposed EEUCB protocol is then compared with various prior techniques. From the result, it can be observed that the proposed EEUCB protocol shows lifetime improvements of 57.75%, 19.63%, 14.7%, and 13.06% against low-energy adaptive clustering hierarchy (LEACH), factor-based LEACH FLEACH, EEFUC, and UDCH, respectively