## 1 Introduction  
The molecular aggregation is a complex phenomenon because aggregate formation is affected by various factors such as molecular concentration [1], pH of solution [2], temperature [3], etc. There is a collaborative effect among the molecular hydrophobicity or hydrophilicity, and solute-solvent and intra-molecular hydrogen bonding [4; 5; 6]. This causes various phenomena relevant to aggregation. \"J-aggregates\" is one of the molecular aggregation phenomena that is accompanied by the red shift in molecular absorption peaks [7; 8]. A J-aggregate was first reported by [PERSON] [9] as a narrow molecular absorption band associated with fluorescence of slightly longer wavelength and named after [PERSON]. Self-assembly such as the molecular aggregation phenomenon is applied to nanodevice development [10; 11], and especially J-aggregates that have an excitonic energy transfer ability that may be used for photovoltaic devices [12]. For the wider application of the aggregation phenomenon, it is important to control the aggregation process and structure of resulting aggregates. However, because the formation of molecular blocks of aggregates occurs spontaneously, it is difficult to control the size and structure of aggregates actively [3; 13]. [PERSON] at el. demonstrated that the structure of aggregates can be controlled by replacing functional groups of the molecule that affect the intermolecular hydrogen bond [14]. Another method is to apply the photochemical process on molecules that are in the aggregation process [15]. Either way, how to affect intermolecular interaction is essential. Light-induced force is a possible means to control intermolecular interaction. The laser-induced crystallization has been studied since the late 1990s [16] and, for molecular aggregation, there are reports of laser-induced aggregation [17; 18]. These studies have been applied for preparing protein crystal samples required for X-ray structural analysis of proteins [19; 20; 21; 22]. On the other hand, optical manipulation was demonstrated for microparticles in 1970s-1980s [23; 24] and the optical trap of nanoparticles has been achieved by other groups as well [25; 26; 27; 28]. In general, the manipulation of nanoparticles is challenging because of its weak optical trapping (gradient force) potential (\(U_{Imp}=\alpha E^{2}/2\); \(\alpha\) is the polarizability of a trapped particle, \(E\) is the electric field of irradiated laser light) against thermal energy (\(k_{B}T\); \(k_{B}\) is the Boltzmann constant, \(T\) is the environmental temperature, which, in the present study, is room temperature 293 K). The weak trapping potential comes from the small polarizability of nanoparticles and the diffraction-limited finite focal spot-size. Furthermore, heating by laser irradiation disturbs the trapping. In spite of the difficulties, expectations are growing for the application of light-induced force for manipulating nanomaterials and controlling nano-structural order [29; 30; 31; 32]. Through the optical manipulation studies, researchers make their efforts on improving the efficiency of optical trapping. Exploiting the surface plasmonic effect is a major way to achieve an efficient optical trap by enhancing the electric field of an irradiated laser beam [33; 34]. In many cases, a metallic nano-gap structure is employed for those attempts [30; 33; 34; 35; 36]. Some researchers contrive how to utilize optically generated heat, which often disrupts optical trapping, by proposing for example the opto-thermoelectric effect due to ions' redistribution by opto-thermoplasmonic fluidics [37]. We previously reported molecular aggregation induced by continuous wave (cw) laser irradiation, which is non-resonant from the main absorption peak of porphyrin molecules, 4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydropyyrin-5-yl]benzenesulfonic acid (TPPS) [38; 39].