Olivier Giroud has completed his £18m move to Chelsea and signed an 18-month contract at Stamford Bridge. Earlier on deadline day Arsenal broke their transfer record for the second window in succession with the £56m signing of the striker Pierre-Emerick Aubameyang from Borussia Dortmund, who in turn took Michy Batshuayi on loan from Chelsea for the rest of the season.

Giroud will wear the No 18 shirt at his new club after his arrival was followed by Dortmund’s confirmation of Batshuayi’s loan. Chelsea have employed a strict policy of not offering long-term deals or contract extensions to players who are over 30 but have bent their rules only slightly to secure the 31-year-old Giroud. He will be in the same position in the summer as David Luiz, Cesc Fàbregas and Pedro with a year to run on his deal, which may prompt negotiations over a 12-month extension.

Giroud said: “I’m​ looking forward to playing. Basically for me the most important thing has been talking with the coach Antonio Conte. I really feel like that he really​ wanted me. He really wanted to work with me.”

Giroud was seated behind the dugouts as the champions took on Bournemouth on Wednesday night. His arrival ends a rather scattergun pursuit of a striker to ease the workload on Álvaro Morata.

Arsenal, who bought Alexandre Lacazette from Lyon last summer in a £52.7m deal, have now further upgraded their attacking options. It remains to be seen whether Aubameyang plays instead of or alongside Lacazette, who has scored nine times for Arsenal in 28 appearances in all competitions. The view at Arsenal is that quality players can always be a foil for each other.

The Gabon international was prolific during his four and a half seasons at Dortmund, scoring 98 Bundesliga goals in 144 appearances. In all competitions he had 141 in 213 matches. Since the beginning of the 2015-16 season the 28-year-old scored 100 goals for Dortmund – 45 more than any player has scored for Arsenal in the same period.

Dortmund said, in a statement to the stock market, they had agreed the “fixed transfer fee of €63.75m” (£56m) with Arsenal for Aubameyang. The sporting director, Michael Zorc, referred to recent “unpleasant episodes” in which the player has been punished for disciplinary reasons but his priority was to highlight Aubameyang’s contribution in the club’s colours.

“Apart from the unpleasant episodes in the past few weeks we would like to remember that Pierre-Emerick Aubameyang at BVB was a real success story,” Zorc said. “In this team, he performed superbly for Borussia Dortmund and scored many important goals and was part of the team that won the German Cup in 2017. We wish Pierre-Emerick all the best for his future at Arsenal.”

Quick Guide Arsenal's whirlwind January Show 9th It emerges Manchester City have bid £20m for Alexis Sánchez 11th Manchester United enter the race for Sánchez and a swap with Henrikh Mkhitaryan is mooted. Francis Coquelin joins Valencia 15th Arsenal confident they can get Pierre-Emerick Aubameyang. Will Olivier Giroud be part of a deal? 17th Theo Walcott signs for Everton 22nd Sánchez-Mkhitaryan swap goes through 28th Chelsea step up Giroud chase 31st Aubameyang arrives for £56m, Giroud heads to Chelsea for £18m, Mesut Özil agrees a new contract Photograph: Paul Jenkins/Action Plus

The transfer has not been without its tensions. Zorc described Arsène Wenger as “disrespectful” two weeks ago, after taking issue with comments from the Arsenal manager about Aubameyang. “Arsène Wenger certainly has enough currently to deal with the performance of his own players,” Zorc added. In Wenger’s defence he had tried to dodge questions on Aubameyang and, in the remarks seized upon by Zorc, he had spoken in only generic terms about the player’s character rather than that of Aubameyang specifically.

Aubameyang posted a message on Instagram apologising for the acrimonious circumstances surrounding his departure but describing himself as a “crazy kid”. He said: “First of all sorry for everything that has happened in the last month. But I wanted a transfer last summer, it did not work, but now it had to. Maybe it was not the best way for me to choose but everyone knows that Auba is crazy – and yes, I am a crazy kid. I’ve made mistakes but never with malice.”

The Gabon striker also revealed his ambitions after completing his move to the Emirates Stadium saying he now wants to emulate Arsenal’s record goalscorer, Thierry Henry. “I think the club has such a big history and great players like Thierry Henry,” he told Arsenal Player.

“He’s an example for us strikers because he was fast and scored a lot of goals. I think I have to work a lot to be like him but I will do. I’m a fast player and I score goals too, like Henry a little bit. But as I said, I have to work a lot more.”

Aubameyang will be reunited with his former Dortmund team-mate Henrikh Mkhitaryan, who moved to north London in exchange for Alexis Sánchez.

“Of course I can join Mkhi in this team, so I’m really happy to be here in this great team,” he added. “I hope that we will come back to the top as soon as possible. I will do my best to join in.”

The transfer for the African Footballer of the Year of 2015 was driven by Arsenal’s new head of recruitment, Sven Mislintat, who used to work for Dortmund. He had been instrumental in signing Aubameyang from Saint-Étienne in 2013. Aubameyang, who underwent his Arsenal medical at 8.30am on Wednesday, is believed to be on a salary of £180,000 a week.

Mislintat has also overseen the arrival of Mkhitaryan – another former Dortmund player – from Manchester United. The attacking midfielder joined in a straight swap with Sánchez. It has been a frenetic January at Arsenal – Wenger has described it as the most “destabilising” he has known at the club – with Theo Walcott also being sold to Everton for £20m and Alexis Sánchez joining Manchester United.

West Brom rejected Arsenal’s approach for the defender Jonny Evans, with the clubs far apart on their valuation of the Northern Ireland international. Arsenal’s offer was some way from the £20m asking price.